Rationale
(Changed due to Application of criteria)
The regional population of Black-bellied Storm-Petrel Thalassidroma (Fregetta) tropica satisfies the criterion for Vulnerable under D2. However, it was felt that it was unlikely that stochastic events or human activities at the Prince Edward Islands would lead to this species becoming Critically Endangered or even Extinct within one to two generations although there was a possibility that such activities could result in this species being listed as Vulnerable or Endangered during that period. As a result, Black-bellied Storm-Petrel was assessed as regionally Near Threatened.
Distribution
This species has a circumpolar distribution, with recorded breeding sites at ten Subantarctic islands or island groups (South Georgia, South Orkney, South Shetland, Bouvet, Prince Edward, Crozet, Kerguelen, Auckland, Bounty and Antipodes islands). Black-bellied Storm Petrels breed in the austral summer (from November) and can disperse as far north as the equator in winter (Onley and Scofield 2007). Within the region, the species breeds on both Marion Island and Prince Edward Island. It is a common passage migrant in waters off the South African mainland, occurring mainly in spring and autumn (Ryan 2005).
Population
There is no recent information available. Brooke (2004) estimated the global population size to be 500 000 individuals (250 000 pairs), although Ryan (2005) provides a lower figure of between 200 000 to 300 000 individuals (100 000-150 000 pairs). It is estimated that there are 5 000 breeding pairs on Prince Edward Island, but the population on Marion Island has not been quantified (Ryan and Bester 2008). Confidence in the regional population estimate is low.
Population trend
The global population is suspected to be in decline owing to predation by invasive species (BirdLife International 2014). However, the regional population trend is thought to be increasing, based on night spotting observations (BM Dyer pers. comm.).
Threats
Predation by alien rats, mice and cats at some colonies may be a problem. It is thought that this bird was extirpated from Marion Island due to predation by cats (van Aarde 1980). Since the removal of cats, there is some evidence that this species is returning to breed (BM Dyer pers. comm.). They may be vulnerable to predation by introduced mice on Marion Island. Light pollution from the research base on Marion Island may blind individuals causing them to collide with unseen structures, injuring or killing them (RM Wanless pers. obs.). There is evidence of an increase in incidents of bird strikes at field huts through collisions with radio antennae cables. Incidents where mortalities have been caused by lights on vessels operating in the Southern Ocean have been recorded (Black 2005). Oil pollution events are a serious risk for a species that actively investigates oil from fish/whales, particularly in search of food.
Conservation
Underway
No conservation measures are underway since the removal of introduced cats from Marion Island, which has proven beneficial to a number of burrowing seabirds nesting on the island. Many general conservation actions and strict guidelines are in place to protect the islands and their native ecosystems. In addition, the Prince Edward Islands are listed as a Ramsar Wetland of International Importance, as a Special Nature Reserve under the Environment Conservation Act (No 73 of 1989) and managed under the Prince Edward Islands Management Plan 1996. The Prince Edward Islands Marine Protected Area was proclaimed in 2013.
Proposed
Eradication of introduced mice from Marion Island should continue, which may encourage this species to resume breeding at this island.
Research
* Accurate and regular population counts are required.
* The degree of movement of birds between the Prince Edward Island colony and other colonies in the Subantarctic region should be assessed.
