84Wildlife Conservation Plan for Seabirds

84 Wildlife Conservation Plan for Seabirds

Introduced stoats (Mustela erminea) are known to prey on burrowing seabirds (Moors and Atkinson 1984, Lyver 2002), and their continued presence in both

remaining colonies is of major concern for the future survival of the species

(Sherley 1992). Initially, stoats were thought to be the primary cause of the species decline (Sherley 1992, Heather and Robertson 1997); however, longer-term research has shown that only a small proportion of adults are taken, and the impact on breeding success could be insignificant (Cuthbert 1999, Cuthbert and Davis 2002). Predation and disturbance by feral pigs and cats are considered a major potential threat but are normally absent from the breeding range (Cuthbert 1999, Taylor 2000, Cuthbert 2002). Habitat degradation and predation by feral pigs (Sus scrofa), along with heavy browsing by a range of introduced herbivores may have been the cause of the complete destruction of some sub-colonies, contributing considerably to habitat loss and range contraction (Sommer et al. 2009).

Incidental capture in set-nets and inshore long-liners is also a concern, with up to 80 individuals being caught in a single net (West and Imber 1985, Darby and Dawson 2000, Harrow 2009). In addition, long-term over-harvesting of some inshore fish species could compromise prey availability to Hutton’s Shearwaters with adverse impacts (Taylor 2000). Modelling has demonstrated that colonies are most vulnerable to the loss of breeding adults; therefore, maintaining high survivorship is paramount (Cuthbert et al. 2001).

Climate change poses a potential threat to the species. Breeding at high altitude makes the species susceptible to detrimental effects of abnormal amounts or timing of snowfall; heavy snowfall can crush burrows, and late snow cover can delay or prevent breeding (Taylor 2000).

Photograph of an adult Hutton's Shearwater in flight

Wildlife Conservation Plan for Seabirds 85

Little Shearwater (Puffinus assimilis)Image unavailable in extracted text

TABLE Species information for the Little Shearwater (Puffinus assimilis)

The Little Shearwater (Puffinus assimilis) is the smallest shearwater resembling other members of the ‘fluttering’ group. The species has a compact structure with a shorter, more slender bill and shorter broader wings with rounder tips. The species has a very large range, occurring in subantarctic, subtropical and occasionally tropical waters. Two subspecies breed in Australia, subspecies assimilis breeds on Norfolk and Lord Howe Island groups and subspecies tunneyi on offshore islands off south-west Western Australia. The species breeds colonially under forest or tussocks. The species also occurs on several New Zealand islands and islands in the Atlantic Ocean. At sea the species is usually solitary or in small groups. They feed by plunge-diving or surface-seizing on cephalopods, crustaceans and small fish.

Brooke (2004) estimated the global population at 200,000 mature individuals. The subspecies tunneyi occurs on 65 offshore islands in Western Australia with an estimated minimum number of breeding pairs between 27,000–61,500 (Burbidge et al. 1996). Subspecies assimilis is endemic to the Lord Howe and Norfolk Island groups. The population of Roach Island (Lord Howe) is estimated at 1,050 pairs with a further 85 pairs on Lord Howe Island (Priddel et al. 2003; Carlile et al. 2013). The population in the Norfolk Island group is estimated at 100–1000 pairs (Schodde et al. 1983; Priddel et al. 2010). Australian trend estimates are unknown.

Predation by introduced rats and feral cats (Felis catus) represents the greatest current and future threat, due to their presence across large portions of the species breeding range in New Zealand and Australia. Little Shearwaters appear to have been greatly reduced in number on Lord Howe and Norfolk Islands. Rat predation affects different subspecies differently, and there is a risk that some subspecies (Puffinus assimilis assimilis in particular) may continue to decline in the future. The continued presence of predators on many islands is likely a contributory factor to preventing recolonisations.

 Minimise effects of climate change

 Examine the relationship between foraging and breeding succuss, population density and productivity and surrounding sea including tracking to determine use of marine habitat in space and time

 Manage key sites to retain their value under climate change

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

 Establish new breeding colonies within former range