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The regional population of White-chinned Petrel Procellaria aequinoctialis has been estimated at 40 000 (33 000-50 000) pairs that breed at Prince Edward Island and Marion Island. The species satisfies the criterion for globally Vulnerable due to suspected and predicted declines over three generations, and the regional population adopts this threat status.
The species has a wide distribution across all the Southern Ocean (Croxall et al. 1984), occurring from the pack-ice of Antarctica northwards to 20°S. It breeds on the French, New Zealand and South African Subantarctic islands, as well as on South Georgia (Islas Georgias del Sur) and the Falklands (Islas Malvinas) (BirdLife International 2014). Within the region, it breeds on two islands namely Marion (290 km2) and Prince Edward (44 km2). Birds wintering off the coast of South Africa represent sub-populations from Crozet, Kerguelen and the Prince Edward Islands (Barquete 2012).
The global population has been quantified at c. 3 million mature individuals (BirdLife International 2014) while Ryan et al. (2012) estimated the global population of the nominate form to be c. 1.1 million pairs. Compared to surface-nesting species such as albatrosses and giant petrels, the world population is poorly known (Ryan et al. 2012). Within the region, a comprehensive assessment of the breeding sub-population at the Prince Edward Islands estimated there to be 21 800-26 000 pairs at Marion and 9 000-15 000 pairs at Prince Edward, giving an estimate of 40 000 (33 000-50 000) pairs in the region (Ryan et al. 2012). The confidence in this estimate is moderate to low.
Trend analysis of the global population from 1980-2054 (three generations, 74 years) predicts a 45% decline based on data from South Georgia and the Crozets (BirdLife International 2014). Population monitoring on Marion Island between 1996-1997 and 1999-2000 recorded a 14.5% per year decrease in the population (Nel et al. 2002) while data from at-sea surveys suggest a 35% decline in the southern Indian Ocean during 1981-2007 (Péron et al. 2010). However, if the ongoing decreases of the largest colony are used, and colonies for which there is no data are assumed to be stable, the global population could decrease by greater than 50% over three generations. Unfortunately, the true rate of decline of the regional population is unknown and the confidence in this trend estimate is moderate to low.
White-chinned Petrels are attracted to ships and their ability to dive as well as their tendency to forage by day and night makes them highly vulnerable to accidental death in longline fisheries (Cherel et al. 1996). An estimated 45 000 per year were killed by longlines in the Southern Ocean Patagonian toothfish fishery, while 8 000 per year were caught off South Africa during the early 1990s at the start of the longline hake fisheries (Barnes et al. 1997). Bycatch in this fishery has decreased substantially since then (Petersen et al. 2009). It is the seabird killed most frequently by the pelagic longline fishery targeting tuna spp. and Swordfish Xiphias gladius off South Africa, comprising around 70% of bycatch birds each year (Petersen et al. 2009). On its breeding sites at the Prince Edward Islands, there are no major threats although the possibility that mice may prey upon chicks cannot be excluded and ongoing monitoring needs to take place (Jones and Ryan 2010). Introduced rats impact populations at some other breeding islands (e.g. Possession Island, Crozets).
BirdLife South Africa's Albatross Task Force is actively researching new technologies to reduce incidental mortality in fisheries, as well as monitoring observer data and estimating annual bycatch in selected fisheries. It promotes the development and enforcement of best-practice to reduce incidental mortality as well as supporting the construction and distribution of devices such as bird scaring lines for fishing vessels. BirdLife International is actively lobbying Regional Fisheries Management Organisations, particularly the Indian Ocean Tuna Commission, to improve the conservation measures required of longline fishing vessels. It is also supporting moves to create regional observer programmes, and strengthen observer data collection and reporting procedures. The species is protected under the Sea Birds and Seals Protection Act, 1973 (Act No. 46 of 1973), Marine Living Resources Act (Act No. 18 of 1998): Publication of Policy on the Management of Seals, Seabirds and Shorebirds: 2007 and the National Plan of Action (NPOA) for Reducing the Incidental Catch on Seabirds in Longline Fisheries (2008). The Prince Edward Islands are listed as a Ramsar Wetland of International Importance, and as a Special Nature Reserve under the Environment Conservation Act (No 73 of 1989) and the Prince Edward Islands Management Plan 1996. The Prince Edward Islands Marine Protected Area was proclaimed in 2013.
Ongoing measures by BirdLife South Africa and BirdLife International, to improve pelagic longline fishing operations and reduce incidental mortality of seabirds should be supported and extended to distant water fishing nations operating in the Southern Ocean. The South African Government should promote international best-practice for reducing seabird mortalities at fora such as the Indian Ocean Tuna Commission and the Commission for the Conservation of Southern Bluefin Tuna. Regional and national observer programmes and reporting of their data remain of paramount importance in understanding the scale of incidental mortality and potential effectiveness of (and level of compliance with) mitigation measures employed. Programmes to repeat the breeding census in a few years' time (possibly through a sub-sampling approach), and tracking birds to assess degree of overlap with various fisheries, remain important tools for assessing and addressing the ongoing threats from fishery interactions.
* The risk of the regional sub-population to various fisheries requires more attention. Currently tracking studies are lacking, but evidence from other sources (Barquete 2012) suggests that appreciable numbers migrate to South African continental waters when not breeding and are vulnerable to longline fishing there. The dispersal patterns, proportional to the population, by sex, age-class and year, and therefore the risks posed to them at each stratum by different fisheries, needs to be quantified.
* Meta-population dynamics between birds breeding on the Prince Edward Islands and those from the relatively nearby French Southern Ocean territories (Crozets and Kerguelen Archipelagos) would help with understanding patterns and relative risks from various fisheries.