Archived 2020 topic: Balearic Shearwater (Puffinus mauretanicus): request for information to resolve conservation status assessment

Please note: This discussion topic is one of a set about species that are endemic or nearly endemic to the European Union (EU), and whose status in the EU therefore effectively determines their global status. To ensure consistency between the 2020 global and EU Red List assessments of these species, this set of topics is being fast-tracked through BirdLife’s Globally Threatened Bird Forums to inform decisions on the EU (and global) status of relevant species, which must be finalised and communicated to the European Commission by mid-April 2020. Topics on other species will be posted on the Forums shortly, for discussion later in the spring, as per usual. The results of the 2020 global Red List update for birds will be published by IUCN and BirdLife in early December.

Balearic Shearwater Puffinus mauretanicus is a Spanish breeding endemic seabird, nesting in multiple colonies on all five major island groups in the Balearic Islands: Menorca, Mallorca, Cabrera, Ibiza and Formentera. The relevant three generation length period for assessing trends in this species under IUCN Red List Criterion A is 42 years (based on an estimated generation length of 13.9 years; Bird et al. 2020).

The species has been assessed as Critically Endangered since 2004, on the basis of demographic modelling, which inferred and projected that an extremely rapid population reduction was taking place and would continue (Oro et al. 2004, Genovart et al. 2016). These models were parameterised using values measured during a long-term study at a single breeding colony (Sa Cella on Mallorca), and predict an annual decline of 14% (Genovart et al. 2016). Further demographic investigation at two islets off Ibiza between 2011 and 2019 also suggested a 14% annual decline (J.M. Arcos in litt. 2020). Mammalian predators do not affect the studied colonies, so it is suggested that declines might be even more severe at colonies where predators are present (Genovart et al. 2016).

As the modelled estimate of population decline forms the basis of the current assessment as Critically Endangered, it is necessary to carefully examine the assumptions within the complex multi-event model presented in Genovart et al. (2016). One concern is that the model is based on a closed population and estimates only ‘local’ survival, rather than taking into account possible emigration to (or immigration from) other colonies. The poor fit of the best global model is explained by the presence of juvenile transients (i.e. birds that leave this colony), which is addressed post-hoc by including age in the models and adding a correction for over-dispersion. However, if adult birds switch colonies (or are simply not observed, in this difficult-to-access sea cave colony), the model appears to treat them as equivalent to dead birds and assigns them the probability of being dead (from bycatch or other causes). As with any estimate of ‘local’ survival in an open population, this approach will underestimate true survival in the absence of any actual mortality. Although breeding site fidelity is likely to be high in this species, it is more likely to be imperfect, as indeed is detection.

A second, related, concern regarding the Genovart et al. (2016) paper is the derivation of the estimates of bycatch mortality, which are almost entirely responsible for the presented population trend projections. The input data for this parameter in the model needs clarification, as the number of bycatch events used is not readily apparent. There are a list of bycatch reports in the supplementary table, but this refers to a separate section. This is a critical parameter, but the standard error is >50%, and the 95% confidence interval is 0.119–0.837, which implies that the predicted rate of decline may be sensitive to this highly uncertain value. Given the scenarios in the discussion of the paper, it seems it is highly sensitive. Lowering the estimated bycatch mortality greatly improves the population persistence (Figure 2, scenarios 3-6 in Genovart et al. 2016). The statement that the estimate of bycatch rate “contains much uncertainty and should be treated with caution” is crucial and should be heeded.

For these reasons, it appears likely that the approach taken in Genovart et al. (2016) would overestimate the actual rate of global population decline. This does not mean that the species is unlikely to be declining. But it does mean that unless a bound of lower and upper plausible rates of estimated decline can be inferred from the modelling, it is not credible (nor in line with the IUCN Red List Guidelines; IUCN 2019) to continue to use an estimate predicting an immediate population crash to assess the extinction risk of this species, despite no evidence of such a crash for two decades.

There is good evidence of rapid, directly observed declines for certain parts of the population. On Formentera, more than 1,500 pairs were present in the early 1990s, declining to fewer than 1,000 pairs in 2001 and 692 pairs in 2003-2006 (Arcos 2011): a rate of decline exceeding 80% over three generations (an annual decline of c. 4% per year). Mammalian predators (cats Felis catus, genet Genetta genetta and Martes sp.) were considered likely to have caused significant adult mortality here, as well as driving local extinctions on Cabrera and causing recorded mortality of adults and nests in the cave colony at Mola de Maó on Menorca (Arcos 2011).

Also, despite the uncertainty highlighted above, there is good reason to believe that rates of bycatch, which principally impacts adults (Cortés et al. 2018), are higher than can be sustained by the species’s known population (Genovart et al. 2016, Tarzia et al. 2017). Using self-reporting logbook information, the estimate of annual bycatch was 622 Balearic Shearwaters in the small-scale fisheries where the risk was highest, concentrated in the pre-breeding and early breeding period (Tarzia et al. 2017). Such a rate of additional mortality is unlikely to be sustainable for a Procellariformspecies, for which adult survival has a high impact on population trajectory (Weimerskirch 2002, Arcos 2011).

The total breeding population size used in the modelling was 7,200 pairs, taking 23,780 individuals as an initial global population size (consistent with at-sea estimates from migration counts from the Gibraltar Strait bottleneck), and assuming demographic equilibrium (Arcos et al. 2012,Arroyo et al. 2016, Genovart et al. 2016). This differs from the estimate resulting from colony estimates (c. 3,000 breeding pairs), as some colonies are either difficult to access or inaccessible, and have only been censused rarely or indirectly, which probably explains the discrepancy in size (Arcos et al. 2017).

However, the post-breeding count data from the Spanish side of the Gibraltar Strait, collected annually since 2008, have recently been analysed and suggest the population is actually increasing (Martín et al. 2019). These counts cover a high proportion of the estimated global population (see Table 1 in Arroyo et al. 2016: over 12,500 individuals directly counted annually), almost all of which are known to leave the Mediterranean after breeding to winter in the NE Atlantic (Guilford et al. 2012). Birds missed due to gaps in monitoring were estimated using Generalised Additive Models trained on the actual count data, resulting in an estimation of effectively the entire global population based on present knowledge (Martín et al. 2019). These estimates of population size were initially supported separately by a boat-based transect method within the Iberian Mediterranean, with good congruence between the results of the two methods (Arcos et al. 2012).

Concerns have been expressed that the land-based survey methodology suffers from the risk of inflating the population size due to potential double-counting, if more localised foraging circuits by some birds result in repeated passes in the same westerly direction on multiple days. However, the similarity in estimates of the larger population size between the land- and boat-based methodologies indicates that there really are a large number of individuals present annually. Crucially, there is no evidence of the rapid declines predicted by the demographic model. It is likely that the land-based counts may lack the precision to detect small population changes, but the trends predicted by the model above are not small changes.

As such, this topic is a request for information to assist with determining the appropriate data to use in reassessing the species’s extinction risk. On one hand, there are annual count-based estimates of an apparently stable or increasing population in excess of 25,000 individuals (of unknown age) passing one location (Arroyo et al. 2016, Martín et al. 2019). One the other, there is a model based on demographic parameters measured at one colony indicating that time to global extinction is c. 61 years (Genovart et al. 2016), and evidence of similar levels of adult survival (0.81) and rates of decline (14% annually) from demographic studies on two islets off Ibiza (J.M. Arcos in litt. 2020).

Using the information from Genovart et al. (2016), and starting with 7,200 breeding pairs (14,400 mature individuals) in 2014, an exponential decline of 14% annually suggests that in 2020 there are now 5,828 mature individuals, in three generations’ time there will be 10 mature individuals, and three generations (42 years) ago there were 2,593,382 mature individuals. Obviously, this rate of decline (99.8% over three generations) would classify the species as Critically Endangered under A2, A3 and A4. As a side note, if we set 14,400 as the global population size in 2004, this rate of decline would mean current mature individuals number only 1,290, or 695 pairs.  

Accepting that the species is stable or increasing, as indicated by the post-breeding counts (Martín et al. 2019), would mean that the species could only be assessed as globally Least Concern. The population far exceeds the threshold (1,000 mature individuals) for listing under Criterion D, which is the only criterion that applies in the absence of a decline or an extremely limited geographic range (IUCN 2012). However, this ignores the observed rate of loss on Formentera (>80% over three generations; Arcos 2011), and requires that this apparent mortality has been offset elsewhere. It also assumes that reported rates of bycatch are not sufficient to impact the overall population, which seems unlikely (Genovart et al. 2016).

Of course, both situations may be true. The breeding colonies studied in the Balearic Islands may be in steep decline, as evidenced by the loss of peripheral colonies and the decline of core colonies. And they may act as population sinks, with ‘floating’ mature individuals replacing others killed each year. But floaters have to come from somewhere, and in order to explain the large and apparently stable numbers counted on passage at the Gibraltar Strait, there must be at least one large additional breeding population which has either been overlooked in the Balearic Islands, or is potentially in a hitherto unsurveyed area, e.g. Algeria (Arcos et al. 2012). Either way, there must be a large number of additional breeding birds within colonies whose demographic rates are superior to those measured to date, such that the species’s overall survival rate has been underestimated.

We need to know what proportion of the global population the apparently rapidly declining studied colonies represent (Sa Cella holds c. 300 mature individuals), and what proportion of mature individuals there are in the post-migration counts (c. 25,000 individuals). Even if we assume that the fraction of mature individuals in the population estimate from Martín et al. (2019) is actually small, immature survival would have to be exceptionally high to offset such a rapid modelled decline (contra values in Genovart et al. 2016). And if immature survival is that high, these birds would then be recruited into the breeding population from three years of age, thus further reducing the estimated rate of decline considerably.

Given the best knowledge available at present, the Red List status of this species warrants reclassification. Without a means of linking the estimates from the demographic modelling to observed estimates of population size and trend, it is not credible to use the headline figure of projected rate of decline from Genovart et al. (2016). On the basis of the recent observed data, it does not appear that current projections could justify suspecting a rapid future decline exceeding 30% over three generations (let alone any higher rate), unless we see evidence of declines at the global population level. However, the uncertainty around the contrasting trends presented suggests that it may be reasonable to suspect a future decline. Taking a precautionary approach, it is therefore possible to suspect that the rate of decline in the next three generations due to exploitation (bycatch) and effects of introduced taxa may plausibly approach 30%, such that Balearic Shearwater could potentially be reclassified as Near Threatened under Criterion A3de.

Relevant comments and information on this fast-track topic are welcome by 8 April 2020, please.

Please note that this forum topic is not designed to be a general discussion about the ecology of the species, but rather a discussion of the species’s Red List status. Therefore, please ensure your comments are relevant to the species’s Red List status and the information requested. By submitting a comment, you confirm that you agree to the BirdLife Forums’ Comment Policy.

References

Arcos, J.M. (compiler) (2011) International species action plan for the Balearic Shearwater Puffinus mauretanicus. SEO/BirdLife & BirdLife International.

Arcos, J.M., Arroyo, G.M., Bécares, J., Mateos-Rodríguez, M., Rodríguez, B., Muñoz, A.R., Ruiz, A., de la Cruz, A., Cuenca, D., Onrubia, A. & Oro, D. (2012). New estimates at sea suggest a larger global population of the Balearic Shearwater Puffinus mauretanicus. In: Yésou, P., Bacceti, N. & Sultana, J. (eds). Ecology and conservation of Mediterranean seabirds and other bird species under the Barcelona Convention. Proceedings of the 13th MEDMARAVIS Pan-Mediterranean Symposium, Alghero (Sardinia). Pp. 84-94.

Arcos, J.M., Alonso, J., López, I. & Mayol, J. (2017). Study, monitoring and conservation of the Balearic shearwater in Spain: an update. Fourth Meeting of the Population and Conservation Status Working Group, ACAP – PACSWG Inf 25 Rev 1.

Arroyo, G.M., Mateos-Rodriguez, M., Munoz, A.R., De la Cruz, A., Cuenca, D. and Onrubia, A. (2016) New population estimates of a critically endangered species, the Balearic Shearwater Puffinus mauretanicus, based on coastal migration counts. Bird Conservation International 26: 87-99.

Bird, J.P., Martin, R., Akçakaya, H.R., Gilroy, J., Burfield, I.J., Garnett, S., Symes, A., Taylor, J., Şekercioğlu, Ç.H. & Butchart, S.H. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology. https://doi.org/10.1111/cobi.13486

Cortés V, García-Barcelona S, González-Solís J (2018) Sex- and age-biased mortality of three shearwater species in longline fisheries of the Mediterranean. Mar Ecol Prog Ser 588:229-241. https://doi.org/10.3354/meps12427

Genovart, M., Arcos, J.M., Álvarez, D., McMinn, M., Meier, R., B. Wynn, R., Guilford, T. and Oro, D., (2016) Demography of the critically endangered Balearic shearwater: the impact of fisheries and time to extinction. Journal of Applied Ecology 53: 1158-1168. https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2664.12622

Guilford, T., Wynn, R., McMinn, M., Rodríguez, A. Fayet, A. Maurice, L., Jones, A. and Meier, R. (2012) Geolocators reveal migration and pre-breeding behaviour of the critically endangered balearic shearwater Puffinus mauretanicus. PLoS One 7 : 1-8. https://doi.org/10.1371/journal.pone.0033753

IUCN (2012) IUCN Red List Categories and Criteria: Version 3.1. Second edition. Gland, Switzerland and Cambridge, UK: IUCN. iv + 32pp.

IUCN (2019) Guidelines for Using the IUCN Red List Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee. http://www.iucnredlist.org/documents/RedListGuidelines.pdf

Martín, B., Onrubia, A. and Ferrer, M. (2019) Endemic shearwaters are increasing in the Mediterranean in relation to factors that are closely related to human activities. Global Ecology and Conservation20, p.e00740.

Tarzia, M. (compiler), Arcos, P., Cama, A., Cortés, V., Crawford, R., Morkūnas, J., Oppel, S., Raudonikas, L., Tobella, C., Yates, O. (2017) Seabird Task Force: 2014-2017. Technical report. Available at www.seabirdbycatch.com.

Weimerskirch, H. (2002) Seabird demography and its relationship with the marine environment. In: Schreiber, E.A., Burger, J. (Eds.), Biology of Marine Birds. CRC Press, Boca Raton, Florida, pp. 115–135.

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30 Responses to Archived 2020 topic: Balearic Shearwater (Puffinus mauretanicus): request for information to resolve conservation status assessment

  1. Daniel Oro says:

    We are here in a challenging scenario: two studies, using different tools and different settings, yield contrasting results. In my view, the two may have biases of different nature, so it is difficult to end up with a reliable conclusion about which one is more correct. Many issues here cannot be lightly discussed in this type of forum.
    It turns out that, as it has been highlighted over the years by the scientific groups working on the species, there is a gap of crucial knowledge on a key parameter: a reliable estimate of population size (and breeding sites). The report above even suggests that there could be breeding animals outside the Balearic archipelago. At the end, we do not know how many breeding females are yet to be discovered at the unknown colonies.
    Trying to summarize, I do not believe that reclassify the species as Near Threatened is a wise, prudent decision. Scientists should properly discuss the results of the Martín et al paper and the demographic papers for ending up with a conclusive report.
    At the same time, a reliable estimation of breeding sites and breeding females needs to be determined once and for all. Downlisting the status does not seem to me the best strategy to solve the lack of this fundamental knowledge we have.

    • Salvador García Barcelona says:

      I agree with Daniel that reclassifying NT to this species will be little useful to improve its knowledge and therefore, its conservation.

      Whatever the discussion that may arise about the accuracy of population survival estimates or fiability of land-based counts, I think that the current classification should not change before the important problem of fishing mortality is solved.

      Knowing that the breeding population is larger than previously believed is good news, but at the same time, the uncertainty existing on the true numbers of breeders suggests remaining vigilant. SEO/BirdLife and other institutions have been studying this problem for years (with difficulties…) to reach a balanced solution for both, seabirds and fishermen. And while this occur, many shearwaters are still caught (some examples of the latest unpublished data collected by observers, all in Catalonia area: November 12 2019, 1 BS; February 5 2020, 35 BS/YS; February 16 2020, 9 BS).

      Fortunately, this is not a widespread problem in the surface longline fleet (García-Barcelona et al, 2010). It is more dangerous in demersal longline fisheries. But in the same way, in both longline gears unpredictable massive catches can occur, and this can wiped out a significant percentage of the population in only one day (García-Barcelona et al, 2016). Therefore it is better to deal this problem if the species maintains its current threat category.

      García-Barcelona S, Ortiz de Urbina JM, de la Serna JM, Alot E, Macías D (2010) Seabird bycatch in a Spanish Mediterranean large pelagic longline fisheries, 2000-2008. Aquat Living Resour 23: 363−371.

      García-Barcelona S, Louzao M, Ortiz de Urbina JM, Juste J, García-Mudarra JL, Camacho E, Macías D (2016) Importance of genetic analyzes to identify the genre Puffinus: a massive catch event as a case study. In: 6th International Albatross and Petrel Conference, Barcelona, ​​Spain, p 173.

  2. Alex Banks says:

    I agree with Daniel’s assertion that we need a reliable abundance estimate, and there is a third option in addition to comprehensive breeding site survey and passage counts: estimating the non-breeding population. I am not sure of the situation with non-breeding surveys at sea in Atlantic Spain, Portugal and France, but we have some data from the UK part of the range we hope to publish soon: is there value in an exercise to collate any recent data over the entire non-breeding range for spatial modelling and abundance estimation? Such an approach might allow inferences about the size of the breeding population, and comparisons with predictions under different demographic scenarios?

  3. Steffen Oppel says:

    This is a very difficult decision, not only because of two apparently conflicting studies, but also because of the generally poorly known population size. I agree with Dani Oro that this is a priority area for future investigation.

    The paper by Martin et al is slightly difficult to interpret because the inference is based on fairly complex models and raw data are only presented in a histogram (in Table A3b) which does not summarise how many birds were actually counted leaving the Mediterranean. If we use the maximum number of birds actually observed flying west (17,874 from Arroyo et al. 2016), and assume that 40-60% of these birds might be breeding adults (a coarse simplification from Carneiro et al. 2020: https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2664.13568 – this could be estimated more precisely with the population model in Genovart et al. 2016), then there seem to be 3500-7100 breeding pairs. This number is already higher than the existing population estimate (3142 pairs), and that is under the assumption that all birds actually migrate past Gibraltar and are counted (which is unlikely). It is therefore reasonable to assume that the existing population is larger than we think it is.

    The count series from Gibraltar is relatively short, and such counts are generally characterised by high variability due to weather and other factors. One useful line of inquiry would be to accept the 14% decline predicted from demographic modelling, project it to the number counted birds, and estimate whether this decline could actually be observed with reasonable power given the variation in count data?

    A very similar situation exists for the Yelkouan Shearwater, a sister species with an equally poorly known overall population size and with migration counts from the Bosphorus that exceed known populations. Because these two species suffer from the same threats (bycatch, predation by invasive species), it would be useful to ensure consistency in any reclassifications between these two species.

  4. I agree with Daniel Oro that reclassifying this species as NT will be little useful to improve its knowledge and therefore its conservation. Whatever the discussions which may arise about the accurate of survival estimates or fiability of counts from land, I think that its current classification not should change before the problem of bycatch have been beaten.

    Knowing that the breeding population is larger than previously assumed is good news, but at the same time, the uncertainty associated with the true numbers of breeders suggests to remain vigilant. SEO/BirdLife and other institutions have been studying this problem for years (with difficulties…) to reach a solution in benefit for both seabirds and fishermen. While this is happening, many shearwaters are still caught (some examples of the latest unpublished data collected by observers, all in Catalonia: November 12 2019, 1 BS; February 5 2020, 35 BS/YS; Feb 16/2020, 9 BS). Fortunately, this is not a widespread problem affecting the surface longline fleet (García-Barcelona et al, 2010), but is located in a specific area of the Spanish coast. It is more dangerous in demersal longline fisheries. But in the same way, in both longlines occur unpredictable massive catches that can wipe out with a significant percentage of the population in only one day (García-Barcelona et al, 2016). Therefore it is better to deal this problem if the species maintains its current threat category.

    References:

    García-Barcelona S, Ortiz de Urbina JM, de la Serna JM, Alot E, Macías D (2010) Seabird bycatch in a Spanish Mediterranean large pelagic longline fisheries, 2000-2008. Aquat Living Resour 23: 363−371.

    García-Barcelona S, Louzao M, Ortiz de Urbina JM, Juste J, García-Mudarra JL, Camacho E, Macías D (2016) Importance of genetic analyses to identify the genre Puffinus: a massive catch event as a case study. In: 6th International Albatross and Petrel Conference, Barcelona, Spain, p 173.

  5. Ricard Gutiérrez says:

    Catalunya (NE Iberia) is well known as one of the main foraging areas for winter months (pre-breeding) and breeding season of the Balearic Shearwater. The situation of the 1990s (Gutiérrez & Figuerola 1995) in which we had observed flocks of up to 7000 birds has not been repeated in recent years, from 2010 to 2020 with one exception, a single flock of 4400 birds seen (by chance for me) off Ebro Delta in January 2016. As the Government in charge of the protection of the species here, we collate winter counts of the species every January which show no recovery at all from the 1990s figures. Maximum counts in last years are 1915 birds in January 2015 and 2167 in January 2018. But 283 birds in 2018, 133 in 2019 and 303 in 2020. The situation is variable and we understand birds may be foraging further S, in Valencia region, following sardines and anxovies. However there is no clear increase in numbers and by no means matching figures of the past.
    To attempt checking other sources of data and see if there is any increase of numbers or flock sizes seen from the coast, we’ve conducted a quick analysis of the ornitho.cat data base which we use for official penal reports. Ornitho.cat database holds 5.914.112 data of birds (up to 6 April 2020) uploaded by 5981 observers, therefore is the best available source of data to see what’s going on from the point of view of field opportunistic observers. We have analysed part of the winter period, from 1 January to 6 April to include 2020 records, in an attempt to see how flock sizes and observations have evolved in these years here. So, from 2010 to 2020, there have been 611 observations of Puffinus mauretanicus with more than one bird involved. Average flock size has varied from 37.68 (In 2014 n=16) to 135.75 (in 2017, n=64), average 78.72. Trend shows fluctuations bewtween years matching peaks recorded in January counts. TRIM analysis of the average flock size for 2010-2020 gives a stable trend because of the fluctuations (multiplicative =0.9884, Sd 0.0119). The issue is that 77,41% of the 611 records of more than one mauretanicus are of 50 or less birds, and only five sightings include more than 1000 birds, with two of 1300 birds (same flock in two different days), one of 1500, another of 2000 and the forementioned of 4400, a size flock I had not seen, or heard about, from the early nineties elsewhere.
    <10 254 41,57%
    11-25 128 20,95%
    26-50 91 14,89%
    51-100 54 8,84%
    101-250 44 7,20%
    251-1000 35 5,73%
    1001-4400 5 0,82%

    There is no direct evidence of an increase of the population in our coasts, believed to be a key area for the foraging strategies of the species.
    For that reason, and following the position of the Spanish Government on the subject, Generalitat de Catalunya is going to include the species as Endangered in our forthcoming official Threatened Species Catalogue.
    Regarding the discussion outlined above, I’d like to concur with the opinions of Dr. Daniel Oro and Salvador Garcia. We are far from knowing the real situation of the whole breeding population. But we know predation by cats and others have affected colonies which are not as safe as Sa Cella. We also know that bycatch is a serious threat and that it has to be addressed. I’d like to include a further item of consideration. There have been recent proven records of Puffinus yelkouan in the Atlantic. As outlined in Gutiérrez (2004) and others afterwards (e.g. in hand DNA sampled birds by Dr. Jacob González-Solís at Barcelona University showing presumed mismatches in genetics-phenotype), the identification of mauretanicus against yelkouan or Menorcan birds is not that easy in all cases. There are also evidences of flocks of yelkouan in the Straits area in the late XX century (via GONHS Ernest F.J.Garcia in litt and photo evidence). Regarding count issue in the Straits of Gibraltar, there could be also a certain, undetermined, percentage of birds not being mauretanicus but yelkouan or ‘Menorcan’ if the birds were distant. Telling adults of both species once worn after breeding is not as easy as recently fledged or moulted.
    All in all we consider withdrawing the threatened status without a proper evidence of an increase of their populations or removing any threat is dangerous for the fate of the taxon. In any case we, as Government responsible of its protection here, despite we have no breeding colonies at all, are not going to diminish its threatened status nor the (difficult) efforts to improve its conservation.
    References

    Gutiérrez R & Figuerola, J 1995 Wintering distribution of the Balearic Shearwater (Puffinus yelkouan mauretanicus, Lowe 1921) off the northeastern coast of Spain Ardeola 42(2) 1995: 161-166 https://www.researchgate.net/publication/259306081_Wintering_distribution_of_the_Balearic_Shearwater_Puffinus_yelkouan_mauretanicus_Lowe_1921_off_the_northeastern_coast_of_Spain
    Gutiérrez, R. 2004. Identification of Yelkouan, Balearic and Manx Shearwaters Birding World 17(3): 111-122
    https://www.researchgate.net/publication/259384578_Identification_of_Yelkouan_Balearic_and_Manx_Shearwaters

  6. Beatriz Martín says:

    I totally agree with Daniel Oro and Steffen Oppel that this is a very difficult decision, and I also think that it is of main importance to find out why estimates at the breeding colonies so largely differ from the estimates we record from land-based surveys at the Strait of Gibraltar. As Daniel Oro pointed out, both type of studies may have biases of different nature, but I agree with Steffen Oppel that, according to land-based surveys and supported by data collected from boats, it is reasonable to assume that the existing population is larger than we think it is, thus the declines projected from studies at the breeding sites (e.g., Genovart et al. 2016) are not taking place at the pace they had envisaged. Apart from the inevitable biases, I am confident on the sampling and the analytical approaches that we applied in the analysis of the counts recorded at the Strait. Due to the different seasonal sampling effort among years and to the undoubtly effects on the counts of weather, a simple comparison of raw data is not enough to provide insights on the trends. According to our own experience in the island of Tarifa, double counts do not seem a major issue in this area. However, our findings (i.e., large interannual variability in the peak of passage in contrast to other Mediterranean shearwater species) show that migration decision in Balearic shearwater must be highly conditioned on environmental factors. In this sense, there could have been a trend in the total number of Balearic shearwaters leaving and not wintering in the Mediterranean in recent years. In this case, we could observe larger number of birds crossing the Strait without (or with lower) increases in the total population size. On the other hand, we all know that Balearic shearwater is a long-lived species highly sensitive to adult mortality and the many threats facing the Mediterranean Sea. Our findings from the Strait also highlight that population trends in this species is complex and non-linear, and intimately bounded to environmental factors that are closely related to human activities. So, in a nutshell, I also agree that we must be cautious in downlisting the species before filling the gaps in our knowledge.

  7. Oliver Padget, Joe Wynn and Tim Guilford says:

    We thank Birdlife for providing researchers with a platform for commenting on the process of IUCN status potential re-assignment of Puffinus mauretanicus, on which we have been working with international colleagues for the last 10 years. We do not think that it is safe to change the species’ status from CR on the basis of a recent coastal counts analysis suggesting that the population is increasing (Martin et al 2019), and despite demographic measurements (principally annual survival) at the Mallorcan colony of Sa Cella, and now similarly at a second colony on the Ibiza archipelago, showing unsustainable decline. The counts data are interesting, but combine different causes of local abundance during the sampling windows. This is not the place for a full and detailed discussion of these issues, which should be properly peer-reviewed, but given the time pressure to respond to the IUCN re-assessment deadline we here report that geolocator data from birds breeding at Sa Cella show that the important assumption that birds are not being double counted is unlikely to be true. Using data from geolocator tracked individuals from our study at Sa Cella we are able to discern the details of longitudinal movements of post-breeding birds through the Straits of Gibraltar with some accuracy despite the inherent latitudinal error associated with GLS. We find, conservatively (i.e. only big, low-error movement), that, on average Mallorcan birds cross westwards through the Strait of Gibraltar 1.39 times during the observation period of Martín et al. (2019). Even more importantly, this varies from an average of 1 time to 2.3 times over the years for which Martín et al. counted and we for which we have geolocator data (2010,11,12,14,17,18). If we expand our analysis to all of the years that we have geolocator data (2010-2018) for the whole migratory period rather than just the dates reported as on effort by Martín et al. (2019), the average number of crossings is between 1 and 3.2 times depending on year. Hence, biological processes influencing the distribution of birds with respect to the Strait (feeding distributions and phenology, not population size) could in theory result in a 2-3 fold difference in population estimate between years. We are happy to provide further details of this preliminary analysis to anyone who requests.

    Thus, coastal counts even at the Strait must include inputs from birds directly leaving the Mediterranean but also birds that are making more local return and re-exit movements, perhaps in association with feeding or social behaviour. These count data were not directly presented in Martin et al., but we were able to re-digitise approximate daily total counts and effort from histograms in the supplementary material. 2018, which has the highest corrected counts reported in study, does not show the clear bi-modal pattern typical in other years, drives the need for the quadratic function in the analysis (and hence necessarily the conclusion that there are increases in recent years), and is itself driven largely by the massive count on just a single day (July 4th) which is more than twice the next highest in the entire study. The apparent population increase (in counts per unit effort or the modelled response to year squared) between 2017 and 2018 is not biologically possible for a Procellariiform since they have a generation time > 4 years (Counts per unit effort: 120% increase in 1 year; modelled increase 88% in 4 years (read from Fig. 3, “year”).

    In short, we still do not have a reliable estimate of population size, either at-sea or in breeding colonies, and we must all work to improve this. Likewise, colony monitoring needs to be increased and standardised to include concentrated cave and more diffuse breeding systems, and we must work to refine our demographic measurements. Given the clear evidence that by-catch is driving massive non-natural mortality, and the most reliable data available showing very low annual survival, it would in our view be very unwise to remove the species’ CR status.

    Oliver Padget, Joe Wynn and Tim Guilford (University of Oxford)

  8. John Croxall says:

    Balearic Shearwater reassessment
    When this was first posted last week, I expressed an immediate concern to the BirdLife Red List Team, but noted that the comments of those most involved/affected should be the important ones to take account of.
    I feel that the BirdLife team has done their best to summarise some of the key issues involved and to set these out in such a way as to elicit responses. However, I doubt whether a matter of such significance can be properly resolved in the timeframe available. To change a species from CR to NT is a massive step, requiring the most compelling of evidence and full consultation with all interested parties. For me the inferences drawn from the material cited does not merit the change proposed. I would also be concerned that analogous approaches to the assessment of data for other GT species could result in quite substantial potential changes for other species.

    Science issues

    1. “Closed” population
    It is exceptionally difficult to measure emigration for seabirds and that this is in balance with immigration (even just to the breeding population) is, for me, a very reasonable default assumption. In procellariforms this is strengthened by the exceptional site fidelity of breeders, such that any imbalance is likely to relate to philopatry of juveniles, which would have at most a modest demographic effect. I also suspect that the main study colony is more likely to attract/retain birds than to lose them, potentially underestimating the population-wide decline.
    2. Bycatch rates
    It is remarkable that multiple estimates of bycatch exist, rather than to focus on the inevitable high variances involved! The difficulty of obtaining any reliable data is notorious. Moreover, almost all such data (except from flag-state-independent observers recording >50% of sets/hauls) is well-known to be considerably underestimated (due to under-reporting and misreporting), often by 100%.
    3. Combined assessment
    Given a perfectly adequate demographic study of a difficult-to-study seabird, resulting in a quantified decline, plus the unquantified (but likely substantial by analogy with other congeners) impact of alien invasive species on other colonies, this species is affected by both of the main on-land and at-sea threats facing seabirds. To move it from CR to NT, essentially on the basis of the data in Martin et al, would seem highly premature, if not inappropriate. It might well be that re-assessment as EN or even VU might be more appropriate but this would require all the scientists most involved to undertake a thorough reappraisal of all relevant data – and this is clearly unfeasible by the existing deadline.

    Other considerations
    1. As essentially a Spanish endemic, Spanish scientists and SEO (for which it has been a flagship species)) need to be fully involved in and content with any status reassessment. Responses to 6 April indicate that this is not the case. There are several past analogue examples for protracted consultation on similar issues this (e.g. with RSPB over Corncrake).
    2. The “high-bar” critique applied to the demographic data for this species could reasonably be expected to be applied to other “declining” seabird (and many landbird) taxa; this would likely reveal many of the same potential problems, as few such data are free of bias and problems in cause-effect attribution.

    3. For now, given the imminent deadline, I can only suggest that the appropriate precautionary position is to retain the existing status. However, this should, in my opinion, be accompanied by:
    a) a clear, brief statement (by BirdLife and based on the existing text) of the issues needing clarification;
    b) the request for a time-limited commitment by all interested parties: (i) to review these issues and to identify what information is needed to resolve them; (ii) pending such resolution, to advise whether any interim change to status at the next appropriate early opportunity) would be merited on the basis of existing data.

    John Croxall
    6 April 2020

  9. LEDARD Michel says:

    7 avril 2020
    The questions raised here are important. The publication by Martin et al. (2019) suggests a stabilization or even a recent increase in the world population of Balearic Shearwater, in contradiction with the publications on the demography of this species, in particular those carried out on the colony of Sa Cella in Majorca (Oro et al. 2004, Genovart et al. 2016 ) showing a very sharp decline (14%) as already quoted on this forum.
    Consecutively to this unique new publication, for which uncertainties and limits are already discussed here, including by the author herself, it seems to us insufficiently justified to abruptly downgrade the Balearic Puffin in LC.
    The adult survival rate plays a major role in the demographic trajectory of this type of Procellariiform species (Weimerskirch 2002, Arcos 2011). However, for this species, this survival rate is very largely impacted by the rate of bycatch by fishing gears. As BirdLife’s analysis states above, the additional bycatch mortality rate is unlikely to be sustainable for this species. However, this subject is still surrounded by uncertainty linked to the lack of data on bycatch rates by fishing gears. In this regard, the latest work carried out in Portugal (Oliveira et al, 2015) is, as for the bycatch data collected along the Spanish Mediterranean coast (Cortés et al., 2017, Tarzia et al., 2017), particularly worrying for the species  and should lead to great caution on the status of the species and to mobilize even more efforts to quantify these rates, over the entire range of the species.
    In France, the “CR” status of the species has led to the preparation of a National Action Plan (as strongly recommended by the SEO 2011 International Action Plan) and has made possible to mobilize professional fishermen representatives. In this framework, we have just submitted a European project (EMFF fund) in partnership with several regional Fisheries Representative Institutions which aims to characterize the interactions between fisheries and Balearic Shearwater, within 6 study sites (for a total area of approximately 15,400 km²) in both Atlantic and Mediterranean waters. Such a program is unprecedented in France and should make possible to assess the mortality rate linked to fishing.
    It is clear that a downgrading in LC would risk weakening the dynamics launched (recent ones in France but also those older in Spain and Portugal) to improve knowledge on this species and to implement conservation actions.
    In conclusion, we suggest, in regards to the uncertainties about the species (in particular those related to population size and bycatch rates), but also in regard to the risk of significantly weakening the conservation initiatives launched in the different countries, to apply the precautionary principle and to keep the current status of the species (CR).
    This would have the double advantage of enabling and maintaining the mobilization of public policies to improve knowledge of the species by filling in major knowledge gaps, and of not slowing down or even stopping the mutilateral partnership dynamics launched for the knowledge and conservation of this species.
    During the next assessment, the data would then be enriched and could thus allow a new reassessment of the status of the species, scientifically more informed.

    Contributors :
    Michel LEDARD – DREAL Bretagne (Regional Representative of French Government) – Responsible for the Balearic Shearwater National Action Plan development
    Mathieu ENTRAYGUES – Office Français de la Biodiversité (OFB) – Responsible for the Balearic Shearwater National Action Plan development
    Nyls DE PRACONTAL / Adrien LAMBRECHTS – Consultants, contributors to the Balearic Shearwater National Action Plan drafting
    Pierre YESOU – Expert associated to the preparation of the Balearic Shearwater National Action Plan
    References
    Arcos, J.M. (compiler) (2011) International species action plan for the Balearic Shearwater Puffinus mauretanicus. SEO/BirdLife & BirdLife International.
    Cortés, V., (2017) Seabirds and demersal longliners in the northwestern Mediterranean: factors driving their interactions and bycatch rates. Marine Ecology Progress Series 565: 116.
    Genovart, M (2016) Demography of the critically endangered Balearic shearwater: the impact of fisheries and time to extinction. Journal of Applied Ecology
    Oliveira, N (2015) Seabird bycatch in Portuguese mainland coastal fisheries: An assessment through on-board observations and fishermen interviews.  Global Ecology and Conservation 3: 51-61.
    Martín, B (2019) Endemic shearwaters are increasing in the Mediterranean in relation to factors that are closely related to human activities. Global Ecology and Conservation, 20, p.e00740.
    Oro D, (2004) Modelling demography and extinction risk in the endangered Balearic shearwater. Biological Conservation
    Tarzia, M. (compiler) (2017) Seabird Task Force: 2014-2017. Technical report. Available at www.seabirdbycatch.com.
    Weimerskirch, H. (2002) Seabird demography and its relationship with the marine environment. In: Schreiber, E.A., Burger, J. (Eds.), Biology of Marine Birds. CRC Press, Boca Raton, Florida, pp. 115–135.

  10. Alejandro Onrubia (Migres Foundation) says:

    I agree with other colleagues in the caution on the drastic change of threat category of the species. However I want to clarify something about the possibility of double counts in the strait. In the counts carried out in the Strait of Gibraltar, we take into account birds flying both west and east, and the estimates of passage are made on the net flow of birds to the west (birds flying West – birds flying East). Practically in all the field days between May 5 and July 15 there are birds “back” to the Mediterranean (flying east), and there are even some days where this flow is majority. For this reason, for the estimates we take into account the net flow to the Atlantic.
    For example, in the year 2017, counting everyday between May 5 and July 20 from 8:00 a.m. to 3:00 p.m., which concentrates approximately 60% of the daily passage, we recorded 18,734 Balearic shearwaters flying west and 2,291 flying to the east, with a net passage of 16,443 shearwaters flying west in that period. We used Generalised Additive Models to estimate the numbers of birds passing during the time periods in which counts were not undertaken (count gaps), and their associated error (Arroyo et al. 2014). Finally, we estimated 25.400 balearic shearwaters.

    The counts carried out in the strait of Gibraltar in the period 2007-2019, show a decrease of the shearwaters in passage until 2012. But, in the last 8 years (2012-2019) the figures show a stabilization, even a slight increase . However, as Dr. Beatriz Martin has commented, the passage numbers in the Strait may reflect population changes, but also changes in the portion of birds that leave the Mediterranean each year, and this depends on environmental conditions.
    For this reason, I agree with other colleagues to handle this information with caution and to be cautious with the change of the conservation status of this species.
    References:
    – Arroyo, G.M.; Mateos-Rodríguez, M.; Muñoz, A.R.; De la Cruz, A.; Cuenca, D. & Onrubia, A. (2014). New population estimates of a critically endangered species, the Balearic Shearwater Puffinus mauretanicus, based on coastal migration counts. Bird Conservation International, 26 (1): 87-99.
    – Martín, B.; Onrubia, A. & Ferrer, M. (2019). Endemic shearwaters are increasing in the Mediterranean in relation to factors that are closely related to human activities. Global Ecology and Conservation, 20: e00740. https://doi.org/10.1016/j.gecco.2019.e00740
    – Onrubia, A.; Martín, B. & Torralvo, C. (2017). Seguimiento del Paso Postnupcial de la Pardela Balear en el Estrecho de Gibraltar para la posible designación de una ZEPA Marinas, en el marco del Proyecto LIFE IP-PAF INTEMARES (LIFE15 IPE ES 012), “Gestión integrada, innovadora y participativa de la Red Natura 2000 en el medio marino español”. Technical Report.
    – Onrubia, A.; Torralvo, C.; Notario, J.; González, C.; Martín, B. & Cano, M.D. (2019). Proyecto Pardelas del Estrecho. Seguimiento de la migración otoñal de la Pardela Balear y Pardela Cenicienta por el estrecho de Gibraltar. Campaña otoñal 2018. Technical Report.

  11. Michel LEDARD says:

    The questions raised here are important. The publication by Martin et al. (2019) suggests a stabilization or even a recent increase in the world population of Balearic Shearwater, in contradiction with the publications on the demography of this species, in particular those carried out on the colony of Sa Cella in Majorca (Oro et al. 2004, Genovart et al. 2016 ) showing a very sharp decline (14%) as already quoted on this forum.
    Consecutively to this unique new publication, for which uncertainties and limits are already discussed here, including by the author herself, it seems to us insufficiently justified to abruptly downgrade the Balearic Puffin in LC.
    The adult survival rate plays a major role in the demographic trajectory of this type of Procellariiform species (Weimerskirch 2002, Arcos 2011). However, for this species, this survival rate is very largely impacted by the rate of bycatch by fishing gears. As BirdLife’s analysis states above, the additional bycatch mortality rate is unlikely to be sustainable for this species. However, this subject is still surrounded by uncertainty linked to the lack of data on bycatch rates by fishing gears. In this regard, the latest work carried out in Portugal (Oliveira et al, 2015) is, as for the bycatch data collected along the Spanish Mediterranean coast (Cortés et al., 2017, Tarzia et al., 2017), particularly worrying for the species and should lead to great caution on the status of the species and to mobilize even more efforts to quantify these rates, over the entire range of the species.
    In France, the “CR” status of the species has led to the preparation of a National Action Plan (as strongly recommended by the SEO 2011 International Action Plan) and has made possible to mobilize professional fishermen representatives. In this framework, we have just submitted a European project (EMFF fund) in partnership with several regional Fisheries Representative Institutions which aims to characterize the interactions between fisheries and Balearic Shearwater, within 6 study sites (for a total area of approximately 15,400 km²) in both Atlantic and Mediterranean waters. Such a program is unprecedented in France and should make possible to assess the mortality rate linked to fishing.
    It is clear that a downgrading in LC would risk weakening the dynamics launched (recent ones in France but also those older in Spain and Portugal) to improve knowledge on this species and to implement conservation actions.
    In conclusion, we suggest, in regards to the uncertainties about the species (in particular those related to population size and bycatch rates), but also in regard to the risk of significantly weakening the conservation initiatives launched in the different countries, to apply the precautionary principle and to keep the current status of the species (CR).
    This would have the double advantage of enabling and maintaining the mobilization of public policies to improve knowledge of the species by filling in major knowledge gaps, and of not slowing down or even stopping the mutilateral partnership dynamics launched for the knowledge and conservation of this species.
    During the next assessment, the data would then be enriched and could thus allow a new reassessment of the status of the species, scientifically more informed.

    Contributors :
    Michel LEDARD – DREAL Bretagne (Regional Representative of French Government) – Responsible for the Balearic Shearwater National Action Plan development
    Mathieu ENTRAYGUES – Office Français de la Biodiversité (OFB) – Responsible for the Balearic Shearwater National Action Plan development
    Nyls DE PRACONTAL / Adrien LAMBRECHTS – Consultants, contributors to the Balearic Shearwater National Action Plan drafting
    Pierre YESOU – Expert associated to the preparation of the Balearic Shearwater National Action Plan
    References
    Arcos, J.M. (compiler) (2011) International species action plan for the Balearic Shearwater Puffinus mauretanicus. SEO/BirdLife & BirdLife International.
    Cortés, V., (2017) Seabirds and demersal longliners in the northwestern Mediterranean: factors driving their interactions and bycatch rates. Marine Ecology Progress Series 565: 116.
    Genovart, M (2016) Demography of the critically endangered Balearic shearwater: the impact of fisheries and time to extinction. Journal of Applied Ecology
    Oliveira, N (2015) Seabird bycatch in Portuguese mainland coastal fisheries: An assessment through on-board observations and fishermen interviews. Global Ecology and Conservation 3: 51-61.
    Martín, B (2019) Endemic shearwaters are increasing in the Mediterranean in relation to factors that are closely related to human activities. Global Ecology and Conservation, 20, p.e00740.
    Oro D, (2004) Modelling demography and extinction risk in the endangered Balearic shearwater. Biological Conservation
    Tarzia, M. (compiler) (2017) Seabird Task Force: 2014-2017. Technical report. Available at http://www.seabirdbycatch.com.
    Weimerskirch, H. (2002) Seabird demography and its relationship with the marine environment. In: Schreiber, E.A., Burger, J. (Eds.), Biology of Marine Birds. CRC Press, Boca Raton, Florida, pp. 115–135.

  12. Miguel McMinn says:

    I thank BirdLIfe for providing this platform for researchers and conservationists.

    I agree with Dani Oro; we need a reliable estimate of breeding sites and their population.

    At this moment surveys are only been carried out in two breeding localities:

    – Eivissa, the islands of Conills and Bledes, this is a project leaded by Pep Arcos of Seo BirdLife,

    -Sa Cella-Dragonera colony, Dani Oro – Tim Guilford. I`m collaborating with this project.

    We lack updated information for the rest of breeding site (see table below).

    Most of the estimates go back to 2008, and the data in some cases is from 2000 (Formentera).

    Resources are urgently needed for updating the information and of these breeding sites. A two-year study of Cabrera found that the population was over 400 pairs (minimum) and that shearwaters were still breeding on the large island of Cabrera. The National Park believed that the balearic shearwater was extinct on the main island.

    Some colonies are inaccessible (Formentera) and probably new techniques will help with the survey (radar, sound recorders, IR cameras).

    However, very little has been done to survey these sites and obtain robust estimates of the breeding population.

    During the 2000 Life Project we soon found out that the large colonies of Formentera had disappeared. Extinction was documented by subfossil remains and testimony the few survivors that used to harvest the colonies. After the Life project we had to give a rough estimate of the breeding population, and I remember discussing this with Dani Oro and SEO. A minimum population estimate was given with the best information we had at that moment. We all knew that more work was needed in the following years to fill in the gaps of information of each site.

    I was very wrong; there has been no continuation of the field work in the colonies. Some of them in natural parks, and one is even a National Park. The only exceptions are colonies of Eivissa and Sa Cella.

    My conclusion is that downgrading he the status does will not help providing the information we need. We should first revisit the known colonies of the Balearic islands. I believe we will find the missing breeding birds.

    By-catch the main cause of non-natural mortality, and predation is still a problem in some colonies (Menorca and Formentera), my suggestion is that it would be unwise to remove the CR status.

    Table of colonies with deficient data:

    Colony, Island, pop estimate pairs, last count/estimate, remarks on estimate % of colony

    na Pobra, Cabrera, 4 pairs, 2008, good estimate 50%

    na Plana, Cabrera, probable, 2008, good estimate 75%

    Conills, Cabrera, 350 pairs, 2008 poor estimate 20%

    Redona, Cabrera, 30 pairs, 2008, poor estimate 10%

    Fonoll, Cabrera, extinct, 2008, good estimate 75%

    Imperial, Cabrera 35 pairs, 2008, poor estimate 10%

    Rates, Cabrera, extinct, 2008, good estimate 75%

    Picamosques, Cabrera, 50 pairs, 2008, poor estimate

    Vedra, Eivissa, 50 pairs, 1995, poor estimate

    Vedranell, Eivissa, probable, 1995, poor estimate

    Tagomago, Eivissa, 200 pairs, 2015, only accesible sites

    Espalmador, Formentera, 16-32 pairs, 2006, good estimate 75%

    Espardell, Formentera, 18-40 pairs, 2006, good estimate 75%

    Punta Prima, Formentera, 50 pairs?, 2003 poor estimate

    Mola, Formentera, 460, 2003 poor estimate

    Barbaria, Formentera, 110, 2003, poor estimate

    Malgrats, Mallorca, 250 pairs, 2009, good estimate 50%

    Conills, Mallorca, 50 pairs, 2009, good estimate 75%

    Fabioler, Mallorca, probable, 2009, poor estimate

    Illa de l’Aire, Menorca, 5 pairs, 2008, poor estimate

    Mola Maó, Menorca, 300 pairs, 2009, poor estimate 10%

    Fornells, Menorca, probable, less than 50 pairs, 2008, poor estimate

    Cavalleria, Menorca, probable 2008, poor estimate

    Son Morell, Menorca, extinct?, no recent information 1995 poor estimate

  13. Maite Louzao says:

    The conservation status of the Balearic shearwater is suggested to be downlisted from Critically Endangered to Near Threatened and experts on the field are required to provide comments in a dramatically short timeframe, without considering any peer-reviewed process. The precautionary principle should be the premise to be applied in conservation science that can have important implications for the management of endangered species, as it is the case of the Balearic shearwater. I disagree with the suggested downlisting due to the following reasons:

    The reassessment of the conservation status of the Balearic shearwater is based on the demographic analyses of Genovart et al. (2016) and trends in the coastal-based counts of Martin et al. (2019). Demographic analysis not only in Mallorca (Genovart et al. 2016), but also in Ibiza (J.M. Arcos in litt. 2020) suggests that both populations have an annual decline of 14%. Based on the precautionary approach, concerns regarding the demographic modelling presented in Genovart et al. (2016) should be clarified (as suggested by the status assessment in relation to bycatch mortality) before changing the conservation status of the species. Genovart et al. (2016) states that the bycatch rate “contains much uncertainty and should be treated with caution”. Bycatch is the main threat for the conservation of the species at sea and many reports and publications have been published evidencing the occurrence of high mass-mortality events of Balearic shearwaters in fishing gears. High mass-mortality events rarely occur (which are characterised by many zeros), but when they occur the number of animals involved is high. Therefore, bycatch data typically follows a zero-inflated distribution, making difficult to reduce the high uncertainty associated to bycatch estimations, even when long-term observer programmes are in place. Following the precautionary approach, the bycatch information hardly collected during the past 20 years should be sufficient to keep the conservation status of the species as Critically Endangered until (1) the uncertainty associated to these estimates is decreased and (2) there are evidences that the fishing bycatch at sea is sustainable for the conservation of the species.
    Regarding the suggested increase of Balearic shearwater population based on Martin et al. 2019, we should first check the possibility of double counting. Tim Guilford’s research team has presented an interesting approach to contrast double counting based on geolocator data. The population monitoring that SEO/BirdLife, IRBI (Iniciativa de Recerca de les Illes Balears lead by David García) and myself have been doing since 2011 in Eivissa (with the help of many collaborators) could be also used to contrast the longitudinal passage of Balearic shearwaters in the Strait of Gibraltar. Since the Balearic shearwaters’s LIFE project in the late 90s, the public funding directed at improving the estimates of population size of Balearic shearwaters has been minimal even whether the species was categorised as Critically Endangered. The inherent difficulty of obtaining accurate colony estimates have been arisen by the reassessment and this should be sufficient to keep the species as Critically Endangered based on the precautionary approach, until the certainty of those breeding population estimates improves.

  14. I totally agree with most comments that have been said in this forum warning it is premature to downlist the species for a substantial number of reasons I am not going to repeat. I would like to start my comment by pointing out that in our freezers at the University of Barcelona we have >300 Balearic shearwaters opportunistically collected from the by-catch of a very limited number of vessels (mainly demersal longliners) over the last 15 years, suggesting what we have is just the very tip of the iceberg. I will then focus on this issue. Several lines of evidence have already been pointed out indicating current levels of by-catch are unsustainable and that birds caught are mostly adults (and there are also some differences in by-catch rates of males and females, basically aggravating the impact of by-catch rates in the population). To add a couple more point on this issue, I would like to briefly summarize some of the information we have recently reviewed for the General Fisheries Commission for the Mediterranean (GFCM), since this has not yet been published. We used records of incidental catches of seabirds presented derived from different approaches, including monitoring programmes with onboard observers, but also from non-systematic, opportunistic data collection such as questionnaire surveys with fishers, tagging/ringing-recovery programmes of seabirds, personal comments of scientists, self-sampling by fishers, beach surveys or recoveries from rescue centres. I would like to highlight two main points:
    Uncertainty in by-catch due geographically uneven records: Overall, the data available on seabird bycatch in fisheries of the Mediterranean and Black Sea are not only scarce, but also unequally distributed. No records could be found for the Black Sea and from African Mediterranean countries. Records from the Western Mediterranean Sea derived from Italy (6.9 percent), and especially from Spain (63.3 percent), where the only known study with regular data collection of seabird bycatch over a long time period (2000–to date) is conducted. This means within the Mediterranean, Balearic shearwaters may be caught in several other countries (i.e. France, Morocco, Algeria, Tunisia, etc.) for which there are no records because there is hardly no one recording bycatch. To this uncertainty we have to add the bycatch recoded in Portugal.
    Uncertainty in the fishing effort of the small-scale fisheries: Most by-catch events of Balearic shearwaters is mainly recorded in small scale longline fisheries. Unfortunately, small-scale fisheries use relatively small boats from 6 to 15 m and therefore many of them are below the length for which positioning systems are mandatory. This implies we cannot estimate the number of birds caught because we do not have a good record of the fishing effort of the small-scale fisheries. It is urgent now to improve the methods for recording fishing effort and incidental catch, particularly in small-scale fisheries.
    Both points mean current estimates of by-catch numbers possibly are a gross underestimation of the reality.

    Until the European Union and the member countries:

    (1) do not solve uncertainty in by-catch rates
    (2) do not solve uncertainly in the fishing effort of small-scale fisheries
    (3) do not force real implementation of mitigation measure for by-catch in all countries

    the Balearic shearwater should not be downlisted (and by extension, the other two endemic shearwaters in the Mediterranean, also strongly affected by demersal longlining)

    Wolf Isbert, Vero Cortes and Jacob Gonzalez-Solis. Seabirds in Carpentieri P., Nastasi A., Sessa M., Srour A. eds. 2020. Incidental catch of vulnerable species in Mediterranean and Black sea fisheries: a review. Studies and Reviews n. 101. Rome, FAO. (Forthcoming)

  15. SPEA doesn’t support downlisting the Balearic Shearwater conservation status, considering the uncertainties related to the population size and the trend of the species. There is no reliable data to support any change in status, which should be maintained for precautionary reasons.

    Downlisting the Balearic Shearwater is proposed after analysing mainly two studies with very different methods, biological parameters and time series length. Although Genovart et al. (2016) is deeply analysed, including the effect of some explanatory variables, the second study (Martín et al. 2019) deserved less exploration of assumptions, achieved results or even overall conclusions. We agree that Genovart et al. (2016) has important limitations to explain the overall demographic rates of Balearic Shearwater, since it is based in only one breeding colony, even if one of the most important for the species, to the best of our knowledge.

    From the other side, we would like to present some explorations on Martin et al. (2019) main assumptions, following the same approach taken above to put into discussion the downlisting of Balearic Shearwater conservation status. This study considers only E-W flying of Balearic Shearwater in Gibraltar Strait, assuming double counts are negligible. Several pieces of evidence point out that such an assumption is quite dangerous. Some previous studies based in coastal counts in Gibraltar Strait have also not taken flight direction in consideration (Mateos and Arroyo 2011) although stating evidence that a portion of birds may fly in W-E direction, back to the Mediterranean (Mateo 2009). Even in smaller numbers, birds flying in W-E direction might be taken into consideration when estimating the total number of birds passing through the Strait (see Arroyo et al 2014). In fact, individual tracking has shown that, at least, Balearic Shearwater adult breeders are using this area more intensively than as just a direct migratory route during the post-breeding (Guilford et al 2012, Austin et al. 2019), either during the beginning or the later phase of this period (Meier et al 2016). In fact, 1 in 10 tracked birds from Menorca Island remained at the Strait Gibraltar area during the entire non-breeding season (Austin et al. 2019). Again, although no signals of birds following NE-SW direction of the shoreline to the East of Tarifa (Mateos and Arroyo 2011), we should highlight those counts were taken during October-November. Moreover, circular movements, that are not possible to record from a single counting point, were reported in other locations where Balearics are known to intensively use during the non-breeding season (Poot 2005).

    Martin et al. (2019) also assume counts during 0800 a.m. and 1100 a.m. period concentrate near 75% of the migratory flux of Balearic Shearwater in the Gibraltar Strait, supporting the appropriateness of the daily counting period. However, a previous work using similar counting data showed an important portion of birds passing through the Strait after that period, namely during the last part of the daylight period (Arroyo et al 2014). Also, at the best of our knowledge there wasn’t any analysis exploring the effects of ecological or environmental variables in the distribution of counts along the day, or at least trying to explain such variance. Neither, it explored possible differences on such passing patterns over different years or along the migratory period. Also, it is not clear if the ratio W-E/E-W is constant along the day and/or along the migratory period. Movements along the night period are not taking into consideration as well, although our current knowledge of birds behaviour at sea are not strong enough to roll out this possibility.

    • Another important assumption, even if indirectly, the studies based in coastal census assume migratory behaviour is homogeneous among years, stating year effect is directly correlated with population size. However, individual tracking of Balearic Shearwaters active breeders showed significant variation in terms of spatial distribution and migratory patterns among years during the post-breeding migration (see differences among Guilford et al 2012, Meier et al 2016, Austin et al. 2019). Actually, a similar effect of year in the post-breeding migration pattern was noted when looking for the raw counts taking from the coastal points located on Tarifa Island (Arroyo et al 2014, supplementary material of Martin et al. 2019), resulting then in high variation in terms of date and magnitude (Martin et al. 2019).

      Although, Martin et al. (2019) found a positive relation between year and number of birds flying E-W through the Strait, assuming then a positive trend, no measure of population size and/or bias for the estimated trend is presented. Greater deviance in the estimates of number of birds passing through the Strait were observed during the years with lesser observation effort when comparing with years with higher observation effort resulting in broader confidence intervals (Arroyo et al.2014). Daily monitoring effort (counting time per day) was stated as equal across years by Martin et al. (2019). Despite figures of annual observation, effort is not provided by Martin et al. (2019), the figure 2 (supplementary material) illustrate a considerably smaller observation effort during 2014 and 2018, and counts were absent in 2013, 2015 and 2016. Actually, observation effort is kept by all trained models and it is one of the most important variables (in terms of coefficient estimate) with a significant effect on count variability in the selected final model. In fact, great numbers for Balearics were counted during a set of 4 different days in 2018 (much above the daily counts observed during the same days of the years before), but it is not clear how the model dealt with such higher counts or how the authors took them into consideration. So, one can assume the positive annual trend resulted by this analysis might have a great amount of unexplained bias.

      Martin et al. (2019) is a very interesting study with remarkable achievements. This study shows important insights of the migratory patterns of Balearic Shearwaters. However, in our opinion it should focus its final contributions on migratory behaviour rather than on population size trends. Coastal censuses are a valuable tool to monitor seabirds in long-term periods, but further analysis and longer datasets should be taken into consideration. Coastal counts in Gibraltar Strait might be considerably improved by monitoring the south segment of the area, setting a similar counting scheme in the African side of the Strait. Also monitoring of night time period might be considered using Radar technology.

      Preliminary data of coastal counts performed from 5 different points along the coast of Portugal Mainland, point a considerable decreasing in raw numbers of Balearic Shearwaters counted from 2009 to 2019 during the post-breeding period (Ana Isabel Fagundes in litt, Sengo et al 2012, Oliveira et al 2014, Fagundes & Filipe 2018, Guedes & Fagundes 2019). Also, at-sea census covering the centre-north coast of Portugal mainland [one of the most used area for the species during non breeding season (Guilford et al 2012, Meirinho et al 2014, Meier et al 2016, Austin et al. 2019)] from 2006 to 2019, during September-November, showed great annual oscillations in terms of mean observed abundance. Census were performed using ESAS methodology and generally following Tasker et al. 1984:

      Year
      Observation effort (km2)
      Abundance (birds*km-2 +/- SD)
      2006-10
      146.00
      0.73 +/- 2.45
      2007-10
      104.54
      0.66 +/- 1.90
      2008-10
      139.62
      4.87 +/- 23.09
      2011-10
      78.49
      0.24 +/- 1.29
      2012-9
      91.82
      2.68 +/- 8.95
      2019-9
      77.06
      2.10 +/- 8.95

      The IUCN Red List criterion A is based on the number of matured individuals only. Estimates derived from coastal counts hardly might detect the portion of mature birds, since age identification of flying birds is hard to achieve. Despite the limitations of Genovart et al. (2016), we believe this study is the best of our knowledge in terms of demographic rates of Balearic Shearwater. The reported negative trend supports the current Conservation status of the species (Critically Endangered), fully agreeing with the negative trend estimated in former analysis (Oro et al. 2004). Following a precautionary approach, the Critically Endangered status should be kept. Perhaps it is also important to refer that following such amount of uncertain in terms of population size and the need to tackle negative impacts of the main threats, both in land (invasive mammal predators) and at sea (bycatch), a project proposal was presented to the last call for LIFE funding, being in evaluation by this time. Also, the project will cover the main range of the species during breeding and non-breeding periods, including partners from all those countries. The approval of this project will also be a great opportunity to deeply discuss the current status of the species.

      Contributions from:
      Ana Isabel Fagundes
      Joana Andrade
      Nuno Oliveira
      Pedro Geraldes
      Vitor Paiva (University of Coimbra)

  16. Meritxell Genovart says:

    The publication by Martin et al. suggests a stabilization or recent increase in the Balearic Shearwater population. I am not going to question here the possible biases of this work. What I am going to do is to clarify some of the biases and flaws that have been attributed to the demographic analysis as this may be crucial for revaluating the species status and to change the decision of the unexpected downgrade of the Balearic Shearwater.
    One of the mentioned concerns about the demographic analysis was about “transients and local survival”. I agree that unfortunately our studies are local and do not take into account dispersal between colonies. However, I do not consider that a critical issue in this particular case. I should mention that in your discussion, you are mixing two different issues: a transience effect and local versus global survival. About the transience effect detected in this species, means that individuals show a lower survival after their first capture occasion and then a higher survival on the subsequent occasions. I am not going to discuss in detail this phenomena, but in relation to what concerns us, our projections assume individuals have the resident survival, the higher one, and thus we take the conservative (optimistic) approach. About the fact that our survival estimate is a “local survival”, I absolutely agree. Is true that we do not take into account dispersal, and some of the local mortality could be in theory dispersal; however, in this case you should accept that if you assume that dispersal is explaining the low adult survival probability then, first, you are contradicting what we know about the species, that the species is highly philopatric. And second, if you accept that many individuals are dispersing, then you should tackle the question about where are those individuals going. Taking into account that there is almost no documentation of dispersal between colonies and that fisheries bycatch has been strongly documented, I consider much more plausible assuming that this low survival is due to mortality.
    One of the main reasons presented to doubt about the reliability of the demographic analysis is that: ”A second, related, concern regarding Genovart et al. (2016) paper is the derivation of the estimates of bycatch mortality, which are almost entirely responsible for the presented population trend projections.” I am sorry but this is absolutely incorrect. The trend projections derive from the survival estimates, not the bycatch estimates. That should be strongly and deeply clarified because probably is the main reason that lead to someone to conclude that there are no clear evidences that point out to the very critical situation for the species. Our survival estimates are robust and point to a critical situation for the conservation of the species. That is clear and has no flaws. Another thing, is our estimate of bycatch effect on mortality. This estimate, indeed, has large confidence intervals and, as we already stated “contains much uncertainty and should be treated with caution”. This is due to the small sample size of marked individuals found dead. This does not mean that people studying this species, especially those working on fishing boats, do not “believe” this estimate; but we should accept that meanwhile we do not have more data, we cannot be more confident about which percentage of mortality in the species is due to fisheries bycatch. But I repeat, to be clear: our projections are based on our survival estimates, that are robust, not on our bycatch mortality estimates. Thus the sentence saying: “Lowering the estimated bycatch mortality greatly improves the population persistence” does not mean that we are basing our conclusions on our bycatch estimates but that we project a hypothetical scenario where survival is much higher than the actual.
    (…)

  17. Meritxell Genovart says:

    In the report is also stated that “.. unless a bound of lower and upper plausible rates of estimated decline can be inferred from the modelling, it is not credible …” The mean growth rate for the population was estimated at 0.856 (95% CI: 0.841–0.872). I cannot imagine the reasons for saying that this is not credible. As suggested in another reply, are you using the same criteria with all the species?
    I also disagree with all the calculations you do regarding the demographic predictions and about how many individuals should be, for example you state “ Using the information from Genovart et al. (2016), and starting with 7,200 breeding pairs (14,400 mature individuals) in 2014, an exponential decline of 14% annually suggests that in 2020 there are now 5,828 mature individuals, in three generations’ time there will be 10 mature individuals, and three generations (42 years) ago there were 2,593,382 mature individuals”, I am sorry but this has not much sense. Population projections are not meant to “exactly predict” how many individuals will be in a certain time. Neither this model not any other. Demographic population models, are not a crystal ball that predicts the future, but an exercise that try to explain what would happen in a certain species or population if conditions where exactly the same that in current conditions. As you imagine, this is a mere exercise to evaluate the conservation status of the species (that may also help to take conservation management decisions), but estimates about the number of years to extinction should not be considered as an exact prediction. On one hand, individuals, species, and populations usually respond to perturbations, and on the other environmental conditions are also variable, thus, things may change, and the most probably situation is that future conditions differ from the originals. As an example, all or some individuals can advance their age of first reproduction or they may change their behavior (for example related to foraging fisheries or stop breeding), the age structure may also change…and also environmental conditions may change, to better, or worse.
    I cannot be sure about the actual or the future status of the species. We may have been missing important information, about unknown colonies, or about individual or population characteristics or behavior, that we are not taking into account on our studies and that would change our conclusions. I accept this widely. But analyzing the situation of the species with our current knowledge (that in my opinion is much more than the available for evaluating most species), what I can conclude is that the situation for the species (at least in those known colonies of the Balearic Islands) seems critical, and reclassifying this species will not help to clarify that situation and may put even more in danger the species.

  18. Pep Arcos says:

    The following is a contribution to this forum on behalf of SEO/BirdLife.

    The issue at hand is an important one, and we believe it’s inappropriate to downlist a CR species, with all the implications that it would have, with such a vague process and tight timeline. More so if the downlisting is huge, from CR to NT, and largely based on an alleged excess of uncertainty (and not strong evidence against the previous CR status assessment). We believe that any reassessment of the species should be conducted through a proper debate, where available data could be evaluated and discussed appropriately. For this reason, and for all the evidence indicating that the Balearic shearwater is in really bad shape, we support the maintenance of its IUCN category as CR.

    The species was assessed as CR in 2004, largely based on a sharp population decline (over 7% per year) according to the first demographic analysis (Oro et al. 2004). This analysis was conducted with data from a unique colony (though an important one, Sa Cella, in SW Mallorca), which was free of predators (unlike other breeding sites). Therefore, the decline was considered conservative, as it could be worse in colonies were rats and, most importantly, cats were present. With the lack of predators, the causes of the decline were assumed to occur at sea, and bycatch was deduced as the most likely factor driving the trend, although at the time, evidence of bycatch occurrence was extremely weak. Over fifteen years later, there has been significant progress in the knowledge of the species, particularly its ecology and threats at sea, and most of this new knowledge supports the suspicions of 2004. Less work has been conducted in the breeding colonies, particularly if we consider that the species is of high concern, but still we have made some advances, with the main weakness being the lack of a proper population estimate. There has been rather little political willingness and commitment, but this is an issue that should be kept aside from this debate.

    I’d like to present an overview of the information available, as well as the associated uncertainties, and defend why the species deserves its current CR status according to such information, and following IUCN criteria. I’ll do in separate posts, as the message is too long.

  19. Pep Arcos says:

    1. Demographic studies.

    After Oro et al. (2004) paper, an update with new information up to 2014 (from the same colony), and new analytical tools, was conducted by Genovart et al. (2016), taking the same colony. This paper showed an even sharper decline, 14% per year, largely due to low adult survival (81%). The study estimates an average extinction time of around 60 years, which certainly would support the assessment of CR (over 80% decline in 3 gerations –previously considered 54 years, now changed to 42 years). This study is severely criticized as an opening to this forum, and we’d like to counter-argue some of the criticisms:

    – This is based in a unique colony, which might not be representative of the whole population. While this is a valid argument, we have to take into account that under a precautionary approach, and considering a species with a restricted breeding range, this information is the unique available and should be taken as a reference. Moreover, the study colony is free of predators, which suggests that the trend in other colonies might be even lower.

    – Despite the above statement, we have recently conducted a new demographic analysis (led by Meritxell Genovart) using data from the western islets of Ibiza between 2011-2019, collected by SEO/BirdLife, IRBI and AZTI, with several collaborations and supports. Again, this is an important colony (Sa Cella-Es Bosc), again free of predators. And the numbers are surprisingly similar: 81% adult survival, 14% declining trend. The results of this analysis will be soon presented to ACAP, which supported this action.

    – Closed population. It is argued that when adults that “disappear” from the monitoring sites are considered “dead”, while they could have migrated to other colonies or might just pass undetected. As John Croxall already counter-argued, Procellariforms are highly philopatric, and once a bird starts breeding in a particular site, it breeds there “forever”. So the emigration to breed in other colonies is highly unlikely at the best, and the assumption of the models is reasonable. It might be that a bird just ceases to breed forever, but from a demographic point of view, this is equal to death. Finally, it’s true that breeding sites are often inaccessible, and a bird might pass undetected. However, birds tend to nest in the same exact location year after year, and it’s unlikely that a bird would pass undetected.

    – The trend is too sharp. It is indeed a sharp trend, and it might seem that counts at sea do not reflect such a change (but see below). On the other hand, the limited colony monitoring conducted allows to detect slight declines of breeding birds in the important colonies (that could work as “sources”, e.g. Sa Conillera), and smaller colonies (likely acting as “sink”) have severely reduced their numbers in recent years (e.g. S’Espardell and Espalmador islets between Formentera and Ibiza. A well-monitored cave in Menorca, which had several nests (most of them inaccessible, but birds could be monitored at its entrance), had a conservative estimate of 30-35+ pairs in the early 2000s, and 1-2 nowadays (in this case, cat predation seems to have played a role). A proper assessment is missing, but there is no evidence of increases nowhere, whereas some colonies are clearly decreasing (and other might be just artificially maintained by recruiting birds from a hypothetical non-breeding pool/immature). Other declines have been previously described, as the one reported for Formentera, and more widely those pointed ou by Miguel McMinn in this forum.

    (to be continued)

  20. Pep Arcos says:

    1. Demographic studies (continuation)

    – Mismatch between breeding and non-breeding population estimates. It’s true that the numbers estimated at sea (around 25,000 individuals) suggest a larger population than that believed to breed (3000 pairs). This issue is dealt with below, but here I’d like to stress that the implications for the IUCN assessment are not relevant. What is important is that we have a declining trend, which would lead to a reduction of over 80% (and even 90%) of the current population in 3 generations, whatever the departing point. It is important to stress that the ms of Genovart et al. (2016) is extremely conservative here, and uses a departing point of 7,200 breeding pairs, instead of the “official” 3000 breeding pairs estimated in the colonies. This figure (7,200) was inferred assuming a global population of around 25,000 individuals. Therefore, the inferred average extinction time might be considered as “optimistic”! By inferring 7,200 breeding pairs we are entrusting that the real figure is 25,000 (which might not be true, although I rather to believe it) and that the population is at equilibrium. But it could be the case that the population is not at equilibrium, and the proportion of non-breeders (juveniles, immature and non-breeding adults) were higher than expected. For instance, Carneiro et al. (2020) describe petrel species where the breeding fraction represents only about 20% of the total population (e.g. Westland Petrel), while the current estimate of 3000 breeding pairs would represent 24% of the global population.

    – Assessment of bycatch as the main driver of decline. This was assessed by Genovart et al. (2016) with considerable associated uncertainty, as stated in the opening of this forum. This is true that the demographic model has no accurate estimates for bycatch, but direct evidence suggest that this is a severe threat likely driving the decline (see below) and, nevertheless, the decline would be occurring, irrespective of which is its main cause.

    – It is important to note that Procellariforms are known for high adult survival, and that survival rates over 0.90 are expected for species such as shearwaters, e.g. the closely related Manx shearwater (Puffinus puffinus) (see Weimerskirch in Schreiber & Burger 2002, and Appendix 2 of that book).

    – Unlike other species, for which population counts are relatively easy to conduct (e.g. gulls) and trends may be established comparing count estimates across years, counting species such as shearwaters and petrels is often complex, and subject to many biases (often inaccessible nesting sites, nocturnal attendance at colonies, etc.). Therefore, using rough population estimates across time to assess trends is highly risky in this type of seabirds, and trends based on demographic information may be more reliable. It is probably important to stress this issue here, to make sure that the use of demographic data is put in its meriting value, and not considered as a mere alternative to what someone might consider a proper population trend assessment.

    Whatever the biases of the available demographic studies might be, both Genovart et al. (2016) and the new assessment of Ibiza (pending of publication) are studies that use state-of-the art modeling tools and provide the best available knowledge on Balearic shearwater trends, conducted by a widely experienced researcher on seabird demography. Even if the trends were overestimated, questioning these results to the point of hardly accepting as possible a decline of 30% within three generations (42 years) is (or should be) beyond the point.

  21. Pep Arcos says:

    2. Population estimates.

    As already exposed, we recognize the apparent mismatch between breeding and global population estimates, assuming that the population is in equilibrium (which might not be the case). Some considerations in this regard.

    – It has been said here that it’s urgent to update the breeding population estimate, with a proper, exhaustive census. This is a challenging task, that might (and should) be conducted as soon as possible. But again, whatever the population, the key issue here is the trend, and this won’t depend on population size. The population assessment will only move up or down the average extinction time, if the current threats are not remediated.

    – It is possible that some breeding sites have been overlooked, and certainly the assessment of known colonies is subject to severe biases, given the inaccessibility of many breeding areas. However, it seems difficult to imagine a population of 7,000 breeding pairs nowadays, and it should be regarded only as hypothetical, under an optimistic scenario (again, stressing the optimism of the available demographic model by Genovart et al. 20016).

    – Data from counts at sea, as well as data from a migration bottleneck, suggest a larger population than previously thought, around 25,000 or even more individuals (Arcos et al. 2012, Arroyo et al. 2014). Available evidence seems to support this view, although both methods claiming such a figure are subject to biases, as already discussed in this forum (see particularly inputs by Tim Guilford and colleagues, and from Nuno Oliveira). However, again, the structure of the population is uncertain, and it might be that a large proportion of non-breeders were playing a role, also buffering a more evident decline at colonies.

    – It has been argued that there must be a “source” population in N Algeria. This idea has been discussed previously, but at present there is no evidence at all of such a population. Actually, Yelkouan shearwaters have been reported to breed in Algeria, and there could have been confusion with Balearic shearwaters. But the available information is extremely limited, and the reported numbers of breeding birds (I insist that these are reported as Yelkouan) are very small (only isolated nests).

  22. Pep Arcos says:

    3. Trends away from breeding colonies.

    As stated by others in this forum, assessing trends away from the breeding colonies may be a valuable indicator. However, this type of information should be taken as complementary, rather than the main way of assessing population trends, as there are many uncertainties related to the lack of information on the structure of the monitored population, and several potential biases associated to this type of estimates. Nevertheless, some considerations on the available information:

    – As stated by some previous contributors, for many areas across the distribution range of the species there is information pointing to a population decline, even if local counts are only a partial picture, and changes in distribution might play a role. So far, Ricar Gutiérrez reported important declines in Catalonia (formerly an important wintering area, as well as an important foraging area during the breeding period), while Nuno Oliveira also presented consistent information showing declines in Portugal. The tight timeline of this forum has precluded to check information from other areas, but so far it seems that the species is going down. Note also the reference of Ricard Gutiérrez to large concentrations of “Yelkouan” shearwaters in the Straits of Gibraltar in the 1970s, which could be related to a far larger population in Menorca at that time, a “lost” population of Yelkouans breeding in N Africa, or just a change in distribution range of Yelkouans from known colonies.

    – A sound argument in favour of the downlisting of the Balearic shearwater is the study published recently on Gibraltar trends (Martín et al. 2019). I have several criticisms regarding that paper, most of them already commented in detail by others, mainly Tim Guilford and colleagues, and Nuno Oliveira. I won’t go into much detail here, but it’s important to stress that this paper infers a trend based on the modeling of migration flow in relation to several “gross” environmental variables, and it’s hard to interpret their results, which are subject to considerable biases. It’d help providing the raw data on which their analysis is based. In fact, as comented by Alejandro Onrubia, the initial years they detected a declining trend. This trend was exposed in the last meeting of the Spanish Working Group on the species (2016), as of 16% decline per year during the post-breeding counts (2007-2012; 2014), and 7% if we consider the pre-breeding counts. After that period, counts in Tarifa (Gibraltar Straits) have been conducted only in 2014, 2017 and 2018, and observer effort has been lower (see comments by Nuno Oliveira, stating that effort was a significant variable influencing estimates in the models).

  23. Pep Arcos says:

    4. Threats.

    It is important to remind that the species is facing serious threats, and that these threats are in place (i.e. the 80% population decline should be taken as a reference). In terms of predators at colonies, the information has been there for at least a couple of decades. But for bycatch, arguably the main driver of the current decline, the accumulated information in the last decade is enormous, as already discussed by others. There is a lot of uncertainty in bycatch estimates, for several reasons. It occurs irregularly, largely in small-scale fisheries for which it’s hard or even impossible to get observers onboard, and even fishing effort or fleet size (by métiers) are unknown, so scaling up bycatch rates is a challenge, subject to huge uncertainty.

    However, bycatch does occur, and causes hundreds or (more likely) thousands of deaths yearly. Just note Jacob González-Solís statement about having 300 dead birds from bycatch in a freezer. Another example, we assessed 657 shearwaters (over 50% of which were Balearic) bycaught in 3 months by only 13 small-scale demersal longline vessels in Catalonia, in the Spring of 2017 (Tarzia et al. 2017). Note also numbers reported by Cortés et al. (2017), among others. And we are collecting information of more and more birds. Add the information from Portugal, where at least hundreds of birds would also be involved (Oliveira et al. 2015). A simple exercise of estimating a Potential Biological Removal (PBR) set a maximum of 125 birds (ICES 2013), and a similar figure is estimated by Genovart et al. (2016), values clearly well below the known bycatch of the species.

    Other threats such as oil pollution, plastics and light pollution might also be playing a role, putting the population under further stress. For now, no proper management plans are in place to tackle threats in protected areas (e.g. Natura 2000 sites), and no regulation is in place regarding bycatch, so there is no reason to think that these threats might go down. Certainly it’s not the case of bycatch, given the current evidence, despite reductions in the fishing fleets.

    5. Breeding area.

    Although the assessment of the Balearic shearwater as CR has been based on IUCN criteria A4, for such an endemic species it is important to recall its restricted distribution range as a breeder. There are quite a few breeding colonies, but the actual area of breeding range is likely below 500 km2 (pending to check), and this alone should suffice to propose the species as Endangered. This is not an argument to keep the CR category, which we support on the basis of all the above evidence, but would help stressing the sensitivity of the species.

    References

    Arcos, J.M. (compiler) (2011) International species action plan for the Balearic Shearwater Puffinus mauretanicus. SEO/BirdLife & BirdLife International.
    Arcos, J.M., Arroyo, G.M., Bécares, J., Mateos-Rodríguez, M., Rodríguez, B., Muñoz, A.R., Ruiz, A., de la Cruz, A., Cuenca, D., Onrubia, A. & Oro, D. (2012). New estimates at sea suggest a larger global population of the Balearic Shearwater Puffinus mauretanicus. In: Yésou, P., Bacceti, N. & Sultana, J. (eds). Ecology and conservation of Mediterranean seabirds and other bird species under the Barcelona Convention. Proceedings of the 13th MEDMARAVIS Pan-Mediterranean Symposium, Alghero (Sardinia). Pp. 84-94.
    Arroyo, G.M., Mateos-Rodriguez, M., Munoz, A.R., De la Cruz, A., Cuenca, D. and Onrubia, A. (2016) New population estimates of a critically endangered species, the Balearic Shearwater Puffinus mauretanicus, based on coastal migration counts. Bird Conservation International 26: 87-99.
    Carneiro et al (2020). A framework for mapping the distribution of seabirds by integrating tracking, demography and phenology. J Appl Ecol 57 (3): 514-525.
    Cortés, V., Arcos, J. M. & González-Solís, J. (2017). Seabirds and demersal longliners in the northwestern Mediterranean: factors driving their interactions and bycatch rates. Marine Ecology Progress Series 565: 1-16.
    Genovart, M., Arcos, J.M., Álvarez, D., McMinn, M., Meier, R., B. Wynn, R., Guilford, T. and Oro, D., (2016) Demography of the critically endangered Balearic shearwater: the impact of fisheries and time to extinction. Journal of Applied Ecology 53: 1158-1168.
    ICES. 2013. Report of the Workshop to Review and Advise on Seabird Bycatch (WKBYCS). ICES, Copenhagen, Denmark.
    Martín, B., Onrubia, A. and Ferrer, M. (2019) Endemic shearwaters are increasing in the Mediterranean in relation to factors that are closely related to human activities. Global Ecology and Conservation, 20, p.e00740.
    Oliveira, N (2015) Seabird bycatch in Portuguese mainland coastal fisheries: An assessment through on-board observations and fishermen interviews. Global Ecology and Conservation 3: 51-61.
    Oro D, (2004) Modelling demography and extinction risk in the endangered Balearic shearwater. Biological Conservation 116: 93-102.
    Tarzia, M. (compiler), Arcos, P., Cama, A., Cortés, V., Crawford, R., Morkūnas, J., Oppel, S., Raudonikas, L., Tobella, C., Yates, O. (2017) Seabird Task Force: 2014-2017. Technical report. Available at http://www.seabirdbycatch.com.
    Schreiber, E.A., Burger, J. (Eds.) (2002) Biology of Marine Birds. CRC Press, Boca Raton, Florida, pp. 115–135.

  24. Salvador García Barcelona says:

    After reading Jacob and Pep comments, just a few more data for updating Balearic shearwater bycatch info in drifting longline fisheries that reinforce the need for implementing a solution to this problem before any change in the classification of the conservation status.

    As I said before, in general, the surface longline targeted Swordfish in the Mediterranean is not a big problem for BS, however Mediterranean fisheries are complex and differ between territories and seasons. In relation to this, though our onboard observer programm, in 2009 we detected a particular case of polispecific sub-métier targeted large pelagics not sampled before. This sub-métier is the responsible of the most of catches of Puffinus on the surface longline since that year. The following values of bycacth contrast with those of 2000-2008, where Puffinus bycatch was nearly absent (this reinforce the importance of a good sampling of the fleet too).

    A simple and rough estimate of annual average BS/YS bycaught by surface longline fleet taking into accunt:
    (1) 2009 – 2018 period
    (2) Métiers and sub-métiers with observed incidence
    (3) Annual average effort of these métiers (aprox. 3.5 M of hooks)
    (4) Average CPUE of Puffinus shearwaters (0.06)

    Resulting in more or less 245 Puffinus shearwater caught by this fleet every year, although some of them will be Mediterranean shearwater and even others are released alive (this information will be known soon)

    Summarizing, the bias in the previous sampling of the fleet (2000 – 2008) shows that is necesary finding a solution to the threat of bycatch before downgrade the threath categorie.

  25. Gonzalo Muñoz Arroyo says:

    This debate undoubtedly highlights the discrepancies between the prior knowledge of the status of this species and the data provided by the new studies, which should lead to increasing research to achieve a more conclusive knowledge of this status, rather than drastically decreasing the Red List status of this species, which would entail less attention to this species.
    It has been well established that the global population of Balearic shearwater must be greater than previously thought, and different evidences converge towards this statement. This led to the need to review the PVA de Oro et al. (2004), which is developed in the new model by Genovart et al., 2016. I am not an expert in population models, but I understand that this, like any model, has a significant burden of uncertainty, particularly because some parameters of the species are not yet known in sufficient detail, such as the percentage of non-breeders, or the effective distribution of their breeding populations (which, once again, calls for more research).
    However, I am surprised by the sharp criticism to this article by Genovart et al. 2016. This paper has gone through a peer review process before being published and Meritxell has addressed in this forum the main concerns exposed. Beyond the exact figure of the rate of decline of the species, there is a bulk of evidences of severe impacts affecting the actual viability of the species, including loss and decreases of known colonies, or unsustainable rates of bycatch affecting adult survival, reflecting the severity of threats to the species (more other projected, as ban of discards). In this context, it is not expected that the species is currently in the most optimistic scenarios of those discussed in Genovart et al 2016.
    Nonetheless, the arguments raised by the Red List Team of BirdLife International to downgrade the threat category rely on a single article (Martin et al., 2019) that shows an apparently increasing trend in the counts of Balearic shears leaving the Mediterranean through the Strait of Gibraltar, about which no criticism is raised. I do not intend to question the results of these authors’ work here. They based their conclusions on relatively complex treatment by modelling the raw count data (I guess no. birds/ hour), allowing them to compensate for the difference in sampling effort within seasons and among seasons in different years. These differences are quite appreciable in some years, and counts are not carried out in three out of the 11 years of the study. All these procedures, being statistically acceptable, generate an unavoidable uncertainty in the results, inherent in most scientific studies. As already mentioned, the results of this study are not easy to interpret, and some information (i.e., results of raw count data) are missing. But, more importantly, whether we focus on Fig. 2.b., it shows that BSh. “abundance exhibited a fall and then a rise in relation to regional environmental conditions, […], indicating that most of the increases have happened recently (from2012; Fig. 2)”. So, best-fit models revealed a sharped decrease of birds counted between 2007 and 2012 (period in which counts were carried out every year with a similar effort, according to Fig. 1.A. in the supplementary material) and a subsequent increase between 2012 and 2018 (period in which counts were only carried out in four of the seven years), rather than a sustained increase throughout the study period. I agree with the comment of Nuno Oliveira, in the sense that the study of Martin et al (2019) is really interesting and provide relevant information about the migratory patterns of Balearic Shearwaters, but I am quite skeptical that these results can be translated into consistent trends for these species, considering the very limited period of time and the constraints of the study.
    As a conclusion, I agree with practically all of the contributors to the debate, in the sense that, in the current state of knowledge, it is not justified and it would be a serious mistake to lower the threat status of the Balearic Shearwater (and even more, so drastically…). In recent years, various Spanish research groups, including SEO BirdLife, are making significant efforts to direct our research to key aspects such as bycatch evaluation or the adequacy and proper management of protected areas for this species, and we are collaborating and “putting pressure” on our Ministry of the Environment to promote the implementation of the national strategy for the species, although resources will always be very limited. Many of these efforts could be frustrated by a hasty decision of Birdlife International. On the other hand, I would claim Birdlife International and other international institutions (eg, ACAP) for greater involvement in research on the potential existence of breeding areas for the species beyond the seas under Spanish jurisdiction, which could solve one of the main gaps in knowledge.

  26. Red List Team (BirdLife International) says:

    Many thanks to everyone who has contributed to this discussion over the past 10 days. We realise that the window for consultation was short (and is now closed), and greatly appreciate the time and effort invested by so many people in commenting, especially during this unprecedented time globally. The volume and variety of responses received on this (and other) species means that it will take us several more days to digest, analyse and interpret everything. We will however do so as quickly as possible, posting our considered conclusions on this species’s status on this page in a final contribution by mid-April.

    Thank you once again, and Happy Easter.

    BirdLife Red List Team

  27. Red List Team (BirdLife International) says:

    Following careful review and consideration of the existing available information, as well as the new information and valuable views shared through the consultation above, we have now reached a decision on the status of this species for both the 2020 global Red List and the EU Red List of birds. Our conclusion is that this species should be precautionarily classified as Critically Endangered (A4abcde) – retaining its current classification, rather than reclassifying it as originally proposed.

    In making this decision, we have endeavoured to take as consistent an approach as possible with that applied to Yelkouan Shearwater P. yelkouan, acknowledging that there are many similarities between these two closely related Mediterranean species. For example, both are long-lived, difficult to study and monitor (as shown by the large discrepancies between population estimates based on colony counts and passage counts), and known to be impacted by bycatch at sea and invasive predators at some colonies. Both are also high priority species for conservation, being listed on Annex I of the EU Birds Directive and numerous other multilateral environmental agreements for many years now, and thus eligible for resources (e.g. EU LIFE funding) that many species are not.

    As set out in the discussion topic, there is good evidence that Balearic Shearwater has declined on Formentera (at a rate exceeding 80% over three generations) and undergone local extinctions on Cabrera. It is also known to be experiencing relatively low adult survival (owing mainly to bycatch) and low breeding success (owing mainly to invasive predators) in at least some colonies. However, the exceptionally steep population decline predicted by demographic models based on data from one (potentially atypical) colony on Mallorca over the past two decades has not (yet) been detectable at the overall population level, while acknowledging the potential limitations of passage counts from the Strait of Gibraltar.

    On this basis, it is possible to justify a one-off exceptional extension to the existing precautionary classification of this species’s status as Critically Endangered, despite the apparent mismatch between the predicted rate of decline and the observed rate of change in numbers of birds. However, this possibility is finite. If a very rapid reduction in the population is not evident and the same situation (in terms of data) pertains when it is next reassessed, then this species will have to be reclassified in line with a less rapid rate of population reduction. Otherwise, IUCN could reject the assessment, as it would not satisfy the requirements of the Red List Guidelines. Note that it is not necessary to conduct a Population Viability Analysis (or equivalent quantitative analysis of the probability of extinction; Criterion E), as assessment against Red List Criteria A to D is more than adequate. IUCN’s requirements for applying Criterion E are both specific and extensive, which is why so few taxa (and no bird species) are currently evaluated using it.

    We therefore encourage all relevant parties and stakeholders to redouble their efforts and to collaborate more closely than ever on this species’s conservation, research and monitoring in the next few years. This includes resolving the discrepancy between the modelled population trajectory and passage counts from the Strait of Gibraltar, but especially increased monitoring of breeding population size and trends at many more colonies (alongside adult survival and breeding success). The aim should be to reach broad consensus on a reliable population size estimate and trend in time for the next round of Article 12 reporting in 2025, with a minimum requirement being the estimation of a plausible minimum and maximum rate of overall population change. Those data will form the basis of the next reassessment of this species’s Red List status in 2026. They should also provide valuable information to assess the effectiveness and impact of measures taken to implement the Species Action Plan – noting that the current plan dates from 2011, and urgently needs reviewing and updating.

    Many thanks once again to everyone who contributed to the discussion above and helped to inform this outcome. The 2020 Red List update for birds including this assessment will be published on the BirdLife and IUCN websites in December.

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