Rationale
(Changed due to Application of criteria)
The regional population of Salvin's Prion Pachyptila salvini satisfies 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 Prince Edward islands would lead to this species becoming severely threatened within one to two generations. As a result it was assessed as regionally Near Threatened.
Distribution
Salvin's Prion occurs throughout the southern Indian Ocean and western Pacific. It breeds at two locations, namely the Crozet Islands and the Prince Edward islands, in the southern Indian Ocean (Jouventin et al. 1984). At South Africa's Marion and Prince Edward Islands, it is the most abundant breeding petrel, forming an important portion of the avian biomass at these islands (Berruti and Hunter 1986). Birds remain in the Southern Ocean for the majority of the year, rarely venturing north of the Subtropical Convergence Zone (Ryan and Bester 2008). It is considered to be a vagrant to South African waters, but may be overlooked given the considerable difficulty of distinguishing prions at sea.
Population
Brooke (2004) estimated the global population to exceed 12 000 000 individuals. Barnes and Huyser (1998) reported the population to be in the 100 000s on Marion Island and in the 10 000s on Prince Edward Island. Ryan and Bester (2008) provide a revised figure of 200 000 on Marion Island and as many as 500 000 on Prince Edward Island, giving a total regional estimate of c. 700 000 individuals. Confidence in this regional population estimate is low.
Population trend
The population is suspected to be stable in the absence of evidence for any declines or substantial threats. Confidence in this regional population trend is low.
Threats
The population on Marion Island was heavily predated upon by introduced cats Felis catus, with approximately 30% of all cat stomachs containing remains of Salvin's Prion while 60% of the 1 224 prey remains identified contained Salvin's Prion (van Aarde 1980). Fortunately this threat has been negated by the eradication of cats from the island (Bester et al. 2002). Chicks are preyed upon by Subantarctic Skuas Stercorarius antarcticus (Berruti and Hunter 1986) which will excavate burrows to reach the nest chamber (Sinclair 1980). It is not known whether introduced House Mice Mus musculus on Marion Island pose a significant threat to the species.
Conservation
Underway
From a global perspective, the Prince Edward Islands are an exceptionally important breeding site for the world's Salvin's Prion population (Ryan and Bester 2008). While no conservation measures specific to this species are in place, the islands are safeguarded by stringent guidelines for visiting researchers. 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 managed under the Prince Edward Islands Management Plan 1996. The Prince Edward Islands Marine Protected Area was proclaimed in 2013.
Proposed
No conservation measures are currently recommended for this species, as there are no longer overt threats in the region. Populations should be monitored regularly, in order to detect any changes in population numbers.
Research
* Severity of predation of prion chicks by introduced mice should be investigated, and if necessary, mitigation measures should be developed.
* A method of accurately estimating population size and densities of burrow-nesting procellariiform seabirds should be developed.
