Cape Gannet Morus capensis is a breeding endemic species of coastal southern Africa, breeding on 6 islands in total. These sites are evenly split between South Africa (Bird [Algoa Bay], Malgas and Bird [Lambert’s Bay] Islands) and Namibia (Ichaboae, Mercury and Possession Islands), although historically it is known to have bred at more sites (Kemper et al. 2007). The species is currently listed as Vulnerable under criteria A2acde+3cde+4acde; B2ab(iii,iv,v) on the basis of its breeding grounds being restricted to six small islands, while threats such as over-exploitation of its food sources by humans, exploitation for food, and pollution have led to rapid declines (see Kemper et al. 2007, BirdLife International 2017).
For a species to be listed as Vulnerable under criteria A2+3+4 the past/ongoing/future decline in the species needs to at least be suspected to fall in the range 30-49% over a three generation period. Recent data, however, shows that the species may in fact be declining at a faster rate than this and so may warrant listing as Endangered. Historically the global population numbered c.254,000 breeding pairs in 1956, which has subsequently decreased to c.249,000 pairs in 1968, c.179,000 in 1989 and c.145,000 pairs in 2005 (Crawford et al. 2007). The most recent population estimate is made up of 10,500 pairs at Ichaboae Island, 2,200 pairs on Mercury Island and 380 pairs on Possession Island (all in 2010) (Kemper 2015), with 81,000 pairs at Bird Island (Algoa Bay), 21,000 pairs at Malgas Island and 8,000 pairs at Bird Island (Lambert’s Bay) (in 2015) (Crawford et al. 2015 updated by R. Crawford in litt. 2016). This gives a global total of 123,080 pairs (roughly 123,000 pairs). While not necessarily a perfect representation of the global population in 2015, it is used as such for ease of trend calculations, and means trends calculated below may in fact be an underestimate of the rate of decline.
These trend calculations give an overall decline of 51.5% between 1956 and 2015, and with only minor extrapolation this would equate to a c.52.4% decline over 3 generations (60.6 years). When comparing the most recent population estimate to the 1968, 1989 and 2005 estimates the annual rates of decline are even higher, and if they were projected to continue into the future then the rate of decline over 3 generations would be c.60%. Therefore, rates of decline over 3 generations more than likely fall within the range of 50-79%, which would meet the threshold for listing as Endangered. Therefore, it is proposed that Cape Gannet be uplisted to Endangered under criteria A2acde+3cde+4acde.
We welcome any comments regarding this proposed uplisting.
BirdLife International. 2017. Species factsheet: Morus capensis. Downloaded from http://www.birdlife.org on 07/04/2017.
Crawford, R. J. M.; Dundee, B. L.; Dyer, B. M.; Klages, N. T. W.; Meyer, M. A.; Upfold, L. 2007. Trends in numbers of Cape gannets (Morus capensis), 1956/1957-2005/2006, with a consideration of the influence of food and other factors. ICES Journal of Marine Science 64(1): 169-177.
Crawford, R. J. M.; Makhado, A. B.; Whittington, P. A.; Randall, R. M.; Oosthuizen, W. H.; Waller, L. J. 2015. A changing distribution of seabirds in South Africa – the possible impact of climate and its consequences. Frontiers in Ecology and Evolution 3: 10, 1–10. doi: 10.3389/fevo.2015.000010.
Kemper, J. 2015. Cape Gannet. In: Simmons RE, Brown CJ, Kemper J (eds) Birds to watch in Namibia. Red, rare and endemic species. Ministry of Environment and Tourism, and Namibia Nature Foundation, Windhoek, pp 149–151.
Kemper, J.; Underhill, L. G.; Crawford, R. J. M.; Kirkman, S. P. 2007. Revision of the conservation status of seabirds and seals breeding in the Benguela Ecosystem. In: Kirkman, S. P. (ed.), Final Report of the BCLME (Benguela Current Large Marine Ecosystem), pp. 325-342.