72Wildlife Conservation Plan for Seabirds

72 Wildlife Conservation Plan for Seabirds

Competition with commercial fisheries potential poses a threat to the species. Over-exploitation of tuna stocks is reducing prey availability (Brooke 2004) as the shearwaters rely on tuna to herd shoals of small fish to the surface where they become available for surface-feeding (Ratcliffe 1999). Human disturbance by visitors to islands where the species breeds have been found to negatively affect breeding success (Benoit and Bretagnolle 2002). Brown Rats (Rattus norvegicus) have in some cases caused local extirpations. Following the eradication of rats from several islands, the species has returned, and is again successfully breeding in these areas (Smith et al. 2006). Small amounts of plastic have been found in Wedge-tailed Shearwater chicks (Verlis et al. 2013). Increased sea surface temperatures have been demonstrated to reduce the provisioning rate, and above a particular temperature threshold reproductive success is nil (Chambers et al. 2011).

 Investigate the locations and characteristics of key feeding sites during breeding and the means to retain their value under climate change

 Quantify impacts of fisheries interactions and human disturbance

Photograph of a Wedge-tailed Shearwater over open ocean

Wildlife Conservation Plan for Seabirds 73

Buller’s Shearwater (Ardenna bulleri)

TABLE Species information for the Buller's Shearwater

Buller’s Shearwater (Ardenna bulleri) is a large, lightly built shearwater closely resembling Wedge-tailed Shearwater (A. pacifica) in size and shape. The species is widespread in the subtropical south west Pacific Ocean and migrates in the non-breeding season to the northern Pacific Ocean, from Japan to North America. The main non-breeding moult zone appears to be the Emperor Seamounts, a chain of underwater volcanos northwest of Hawaii (BirdLife International 2019). The species occupies a range of marine habitats from inshore to shelf-edge and oceanic zones. The species is a breeding endemic to New Zealand, occupying a variety of habitats on the Poor Knights Islands (Aorangi and Tawhiti Rahi). It nests in burrows or on rock-crevices and ledges, often under dense vegetation. It feeds on krill, small fish, salps and jellyfish (Marchant and Higgins 1990, Heather and Robertson 1997).

The total population has been estimated at 2.5 million birds (Marchant and Higgins 1990), although this is now regarded as too high (Waugh et al. 2013; BirdLife International 2019). Between 1938 and 1981, the population on Aorangi increased from approximately 200 to 200,000 pairs (Harper 1983, Heather and Robertson 1997). However, surveys in 2011-13 suggested that there are around 100,000 burrows, similar to estimates in 1960s (Waugh et al. 2013). The species is listed as vulnerable by the IUCN Red List.