78Wildlife Conservation Plan for Seabirds

78 Wildlife Conservation Plan for Seabirds

The species is at risk from incidental capture in longline, trawl and gill-net fisheries and suffers the additional effects of depletion of prey stocks (Uhlmann 2003). A large number of deaths occur as a result of interaction with fisheries both during the breeding season and the winter migration to the Northern Hemisphere (Uhlmann 2003). The species is also subject to a legal cultural harvest in New Zealand. Harvesting of young birds ('muttonbirding') currently accounts for the take of around a quarter of a million birds annually (del Hoyo et al. 1992, Heather and Robertson 1997, Newman et al. 2008, 2009), but is unlikely to account for the scale of the observed decrease.

Past investigation into the biological impact of climatic trends led to predictions of large-scale shifts in foraging distribution during the boreal summer and/or dramatic reductions in abundance and survival rate (Ainley et al. 1995, Veit et al. 1996, 1997, Spear and Ainley 1999, Wahl and Tweit 2000, Oedekoven et al. 2001, Hyrenbach and Veit 2003). Climate change is already affecting the foraging distribution of this species along the Californian coast (Veit et al. 1997). Evidence shows that birds are still visiting many of the same foraging areas, but are taking new routes to avoid altered current systems (Veit et al. 1996, 1997). Decreases at monitored breeding sites appear to be linked to changed patterns in large scale oceanic cycles which reduce prey availability (Clucas 2011).

Brown Rat (Rattus norvegicus) and Black Rat (R. rattus) are present on some islands on which the species breeds, and although egg and chick predation by rats has been demonstrated, the extent of impact is unknown (Jones et al. 2008).

 Assess the impact of bycatch from gill-nets, longlines and trawl fisheries across the range and apply appropriate mitigation techniques

 Implement best practice quarantine measures at breeding colonies to reduce the risk of any invasive species (re)establishing on islands

Wildlife Conservation Plan for Seabirds 79

Short-tailed Shearwater (Ardenna tenuirostris)

TABLE Species information for the Short-tailed Shearwater

Life History and Distribuion

The Short-tailed Shearwater (Ardenna tenuirostris) is a medium sized all brown-grey shearwater, very similar to the larger Sooty Shearwater (A. grisea). The Short-tailed Shearwater undergoes a trans-equatorial migration, wintering north of Japan and the Bering Sea near the Aleutian Islands (USA) (Carey et al. 2014). The return migration pathway incorporates the central Pacific Ocean, with some individuals moving south along the western coast of North America. This species breeds on Tasmanian offshore islands and off the coast of southern Australia, with the bulk of the population in the south-east. Breeding occurs mainly on coastal islands, typically in areas of grassland or other vegetation, but sometimes cliffs or bare ground (del Hoyo et al. 1992). While breeding, the species alternates short foraging trips to local waters with long foraging trips (up to 17 days) to the Polar Frontal Zone. Short trips allow greater chick provisioning, longer trips allow foraging at the Antarctic Polar Front, reducing competition close to the breeding grounds. Diet includes fish (particularly mycotphids), crustaceans and squid (Weimerskirch and Cherel 1998). Feeding occurs in very large flocks and it regularly feeds in association with other shearwaters, petrels, gannets and terns.