Rationale
(Changed due to Criteria revision)
The regional population of Blue Petrel Halobaena caerulea breeds at two locations in the region namely, Prince Edward Island and Marion Island, therein satisfying the criterion for regionally Vulnerable under D2 (population with a very restricted area of occupancy or number of locations (typically five or fewer) such that it is prone to the effects of human activities or stochastic events within a very short time period in an uncertain future, and is thus capable of becoming Critically Endangered or even Extinct in a very short time period). However, it was felt that it was unlikely that stochastic events or human activities at the well-managed Prince Edward Islands would lead to the Blue Petrel's conservation outlooks becoming severe within one to two generations. If threats intensify there is a possibility that the species may become regionally Vulnerable or Endangered during that period. As a result Blue Petrel was assessed as regionally Near Threatened.
Distribution
The Blue Petrel has a circumpolar breeding distribution at subantarctic islands (Weimerskirch et al. 1989). Outside the breeding season, birds disperse widely throughout the Southern Ocean (Ryan 1997). The species is an irregular, non-breeding vagrant to South African waters occasionally irrupting in large numbers (Ryan 1997).
Population
Studying the breeding biology of burrow-nesting seabirds requires accurate identification of burrow occupants and nest status, which can be difficult (Hamilton et al. 1998), and complicates estimation of population numbers. Brooke (2004) estimated the global population of the Blue Petrel to number at least 3 000 000 individuals. Ryan and Bester (2008) provide an estimate of 100 000 birds on Marion Island and 200 000 birds on Prince Edward Island, suggesting a regional breeding population of 300 000 birds. Confidence in this estimate is low.
Population trend
The global population is assumed to be stable (BirdLife International 2014). Breeding success has increased on Marion Island since the eradication of cats in 1991 (Cooper et al. 1995). The breeding population on Prince Edward Island is thought to be stable in the absence of major threats.
Threats
The regional population decreased due to predation by cats on Marion Island (Van Aarde 1980). Following the removal of cats on the island the breeding success increased from 24% to 64% (Cooper et al. 1995). The Blue Petrel is one of few burrowing petrels for which mouse predation on chicks has been confirmed (Fugler et al. 1987, Wanless et al. 2007). Barbraud and Weimerskirch (2003) suggest that climate change will impact strongly on seabird populations, including the Blue Petrel, after reporting that long-lasting warming caused a c. 40% decline of the Blue Petrel.
Conservation
Underway
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. Various stringent guidelines are in place to prevent pollution, contamination, disturbance and introduction of pathogens or invasive organisms on the islands.
Proposed
The Blue Petrel is known to be vulnerable to predation by introduced mice at Marion Island (Fugler et al. 1987). Eradication of mice would likely improve breeding success and generally restore the ecology of the island (including potentially increasing other burrowing petrel numbers and altering Subantarctic Skua Stercorarius antarcticus numbers and their predatory behaviour on burrowing petrels), and is therefore strongly recommended.
Research
* Information is required on population numbers and trends on the Prince Edward Islands; virtually nothing is known about the basic demography of this species.
* Knowledge of breeding success, recruitment parameters, longevity, breeding frequency, sex-based differences in parental investment, age/sex structure, etc. would be useful for modelling population trends; currently all this information would have to be inferred from other areas or sister taxa.
* Movements of this species are unknown, including the geographical range of juveniles.
