|Scientific Name:||Thalassarche chlororhynchos|
|Species Authority:||(Gmelin, 1789)|
|Taxonomic Notes:||Diomedea chlororhynchos (Sibley and Monroe 1990, 1993) has been split into chlororhynchos and carteri and both placed in the genus Thalassarche following Brooke (2004).|
|Red List Category & Criteria:||Endangered A4bd;B2ab(v) ver 3.1|
|Reviewer(s):||Taylor, J. & Butchart, S.|
|Contributor(s):||Cooper, J., Cuthbert, R., Hilton, G. & Ryan, P.G.|
|Facilitator/Compiler(s):||Anderson, O., Butchart, S., Calvert, R., Small, C., Sullivan, B., Symes, A.|
This species is listed as Endangered as it has a very small breeding range and is estimated to be undergoing a very rapid ongoing decline projected over three generations (72 years) owing to incidental mortality in longline fisheries.
Thalassarche chlororhynchos breeds on Gough and islands in the Tristan da Cunha archipelago, Tristan da Cunha, St Helena (to UK). On Gough, the population was estimated at c.5,300 breeding pairs in 2000-2001 (Cuthbert and Sommer 2004a). In the Tristan da Cunha Island group, the number of breeding pairs per year was estimated to be 16,000-30,000 on Tristan da Cunha Island in 1974, 4,500 on Nightingale Island in 1974, 40 on Middle Island in 2010 (Ryan et al. 2011), 210 on Stoltenhoff Island in 2010 (Ryan et al. 2011), and 1,100 on Inaccessible Island in 1983 (Fraser et al. 1988). A count in 2007 on Nightingale Island re-estimated the population at 4,000 breeding pairs (ACAP 2009). These data give a total of 27,500-41,600 breeding pairs per year, equating to 55,000-83,200 mature individuals. However, given that the Tristan da Cunha data are now over 30 years out of date, there is considerable uncertainty around the overall population estimate. Trend data from study colonies on Tristan was used to produce a revised estimate of c.3,250 pairs in 2001 (Cuthbert and Sommer 2004), equating to a reduction of 80-89% from 1974 levels to 2001. This figure suggests an updated population estimate of c.13,900 breeding pairs, equating to 21,000-32,000 mature individuals, may be more appropriate. Demographic data have been collected from two study colonies on Gough Island and Tristan da Cunha. Annual variation in the number of breeding birds was strongly correlated between the two islands and over the whole study period both study populations have decreased at around 1.1-1.2% per year (Cuthbert et al. 2003). However, population modelling predicts annual rates of decrease of between 1.5-2.8% on Gough Island and 5.5% on Tristan da Cunha (Cuthbert et al. 2003). On Inaccessible Island, a partial count in 1999-2000 suggests that the population may have decreased since the late 1980s (Ryan and Moloney 2000). In the non-breeding season it disperses throughout the South Atlantic Ocean, mainly between 25°S to 50°S, and has been recorded off the coast of Argentina, Brazil and the west coast of southern Africa (Harrison 1983). A single bird collected at Middle Sister Island (Chatham Islands) in the 1970s had recently laid an egg.
Native:Angola (Angola); Argentina; Brazil; Mozambique; Namibia; Saint Helena, Ascension and Tristan da Cunha; South Africa; Uruguay
Vagrant:Australia; Falkland Islands (Malvinas); New Zealand; United States
|Range Map:||Click here to open the map viewer and explore range.|
On Gough Island, the population was estimated at c.5,300 breeding pairs in 2000-2001 (Cuthbert and Sommer 2004). In 1974, the number of breeding pairs in the Tristan da Cunha group was estimated to be 16,000-30,000 on Tristan da Cunha Island, 4,500 on Nightingale Island, 100-200 on Middle Island, 500 on Stoltenhoff Island (all data from 1974: Richardson 1984), and 1,100 on Inaccessible Island (in 1983, Fraser et al. 1988). However, these data are now >30 years out of date and there is considerable uncertainty around the overall population estimate. It is likely that most populations are considerably reduced since 1974 counts, particularly on Tristan da Cunha Island (estimated to be c. 3,250 in 2001), based on population trend data from study colonies (Cuthbert and Sommer 2004). This equates to a reduction of 80-89% from 1974 levels to 2001. More recent data reports 40 pairs on Middle Island and 210 on Stoltenhoff Island in 2010 (Ryan et al. 2011). Based on the recent trend figures, a more appropriate estimate of total breeding pairs might be 13,900, equating to 27,800 mature individuals (and a range of 21,000-32,000).
|Habitat and Ecology:||Behaviour This species is an annual breeder. Nests are a pedestal made of mud, peat, feathers and vegetation. Eggs are laid September to early October, and chicks fledge in late March to April. Young birds return to colonies from five years of age, and experienced breeders will attempt to breed in two of every three years. Breeding success ranges from 62-72% and 62-76% for Gough Island and Tristan de Cunha respectively (ACAP 2009). It usually breeds singly or in loose aggregations. It feeds by surface-seizing and occasionally diving, and also feeds in association with marine mammals or gamefish which bring baitfish to the surface. It is strongly attracted to fishing vessels and studies from shelf waters have shown scavenged food can comprise a large proportion of stomach contents. Habitat Breeding It builds nests built on tussock grass, on rocks and under trees. Diet When not scavenging, its diet is largely comprised of fish, but also cephalopods (ACAP 2009). In one study, cephalopods were predominant in the diet of birds caught by longlines, representing 73% of the total mass (Colabuono and Vooren 2007).|
|Major Threat(s):||This species is commonly caught as incidental bycatch in longline fisheries within its range. In particular, there is an estimated mortality of at least 900 birds per annum off the coast of south-east Brazil, where it is known to be one of the commonest species attending longline vessels (Olmos et al. 2000). It is also known to attend trawlers and longlining vessels off the west coast of southern Africa (Harrison 1983, Olmos 1997, Croxall and Gales 1998), where mortality has been recorded (Ryan et al. 2002). It is thought to be one of the most frequently killed species in pelagic and longlining fisheries off Namibia where assessments of seabird bycatch are just emerging (ACAP 2009). The harvest of chicks and adults on Tristan, previously permitted under a local ordinance, is now illegal and poaching is now probably rare. Although house mice Mus musculus and black rats Rattus rattus are present on some breeding islands they have no known effects on breeding success. Inaccessible Island no longer has feral pigs Sus scrofa, which would likely have impacted adults, chicks and eggs (ACAP 2009).|
Conservation Actions Underway
CMS Appendix II and ACAP Annex 1. It is monitored on Gough Island. Gough and Inaccessible Islands are nature reserves. Gough Island is a World Heritage Site. A population census was conducted in 2000-2001, and a repeatable monitoring protocol was devised (Cuthbert and Sommer 2004b). Remote-tracking of the Gough population took place during 2004-2005, to determine at-sea distribution. Remote-tracking of the Tristan da Cunha population is being undertaken in 2007-2008. Limited counts were made in a few areas of Tristan da Cunha during 2004 and limited monitoring is ongoing. In 2006 the South East Atlantic Fisheries Commission (SEAFO) passed a resolution to require all its longline vessels to use a tori line and to set lines at night. Conservation Actions Proposed
Census the population on all the islands in the Tristan da Cunha group. Conduct regular monitoring of a more representative proportion of the population and continue monitoring on Gough Island. Assess recent population trends, demographic parameters and modelled trajectory of population. Determine the at-sea distribution of the species through tracking studies (BirdLife International 2004) and the interaction with longline fisheries. Promote the adoption of a) monitoring of seabird bycatch associated with longline fishing and b) best-practice mitigation measures in all fisheries within the species' range, particularly via intergovernmental mechanisms such as ACAP, the FAO, and Regional Fisheries Management Organisations, including the Atlantic tuna commission (ICCAT) and the South East Atlantic Fisheries Commission (SEAFO).
|Citation:||BirdLife International 2012. Thalassarche chlororhynchos. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 05 September 2015.|