Assessing the impacts of fishing and habitat loss on the Lord Howe Island population of flesh-footed shearwaters

The flesh-footed shearwater Puffinus carneipes is a medium-sized seabird with a single eastern Australian population breeding on Lord Howe Island. Other breeding populations exist in New Zealand, south-western Western Australia and St. Paul Island in the Indian Ocean. Tagging and banding studies indicate that breeding birds of the Lord Howe Island population inhabit waters mainly to the west of the Island during October to May. Birds then migrate north to waters surrounding Japan during the Austral winter. Seabirds are attracted to the baited hooks of longline vessels and can become snagged and drown as the line sinks into the water. Observations of flesh-footed shearwater (FFS) bycatch in Australian waters have been recorded on both Japanese and domestic longline fishing vessels. Increased observer coverage between 2002 and 2004 on Australian longline vessels, in order to monitor the effectiveness of an under-water setting chute and various line-weighting regimes, showed large bycatch rates of seabirds, and in particular flesh-footed shearwaters (Baker and Wise, 2005). In addition, substantial reductions in colony size have occurred on the island due to housing development. As a consequence of these sources of additional mortality, concerns have been expressed about the population's sustainability. Australia has international and national obligations to ensure that fishery interactions with seabird populations are not deleterious to their populations. The “incidental catch (or by-catch) of seabirds during oceanic longline fishing operations” has been listed under the Environment Protection and Biodiversity Conservation Act 1999 as a key threatening process for seabirds (Environment Australia, 1998). Flesh-footed shearwaters were nominated as being at risk from longline fishing. This paper presents a quantitative impact assessment that fully integrates information on the biology, foraging distributions, links to oceanography, fishing interactions (Northern and Southern Hemisphere), and potential impacts from housing on Lord Howe Island. A discrete age-, sexand colony-structured model is developed that accounts for natural and fishing mortality, together with potential consequences from the loss of nesting habitat on Lord Howe Island. The model is able to fit to tagging data on breeding foraging distributions. These data assist the model in predicting where the birds might be when at sea. The birds’ position is assumed to be a function of time of year, sea surface temperature and longitude. Using the predicted positions, the model fits to data on the observed bycatch from the Australian domestic longline fishery. These data enable the model to predict the probability of catching a bird, given various operational characteristics (e.g. setting at night). The model also fits to data from the two surveys of breeding abundance that have occurred on Lord Howe Island.