ESTIMATING FISHERY BYCATCH AND EFFECTS ON A VULNERABLE SEABIRD POPULATION

Pelagic longline fisheries worldwide incidentally take long-lived seabird species. This mortality has led to fisheries restrictions to protect seabirds at risk, including Wandering (Diomedea exulans) and Amsterdam Albatross (D. amsterdamensis) in the South Pacific and Spectacled Petrel (Procellaria conspicillata) in the South Atlantic. Because pelagic longline fisheries involve multinational fleets operating in vast ocean regions, assessing total bycatch levels for a seabird is challenging. Here we present a case study of quantifying bycatch from a basin-wide pelagic longline fishery and assessing the population-level impact on a vulnerable seabird, the Black-footed Albatross (Phoebastria nigripes) in the central North Pacific. We develop an assessment method that uses observer data to estimate bycatch for one fleet and then uses scenario analysis to estimate bycatch for remaining fleets. Our method generates a bounded estimate of bycatch within an ocean region, ranging from the worst-case to the best-case bycatch scenario. We find that Black-footed Albatross mortality across all fleets in the central North Pacific may total as much as 10 000 individuals/yr. At this level of mortality, population declines are likely. However, even at the best-case bycatch estimate (5200 individuals/yr), population declines may occur over the next three generations (60 years). Although this analysis requires extensive estimation and extrapolation from existing data, it is critical to provide fisheries managers with bounded estimates of likely population-level effects of current fishing activity. Corresponding Editor: Paul Dayton