The status of seabird populations is deteriorating faster compared to other bird groups, and bycatch in fisheries is identified as one of the principle causes of declines (Croxall et al., 2012). The problem of seabird bycatch in gillnet fisheries has long been known in the Pacific, Atlantic oceans and Baltic Sea (Tull et al., 1972, Ainley et al., 1981, Piatt and Nettleship, 1987 and Stempniewicz, 1994), and gillnets have been the cause of some of the highest recorded mortalities of seabirds worldwide. In the North Pacific, drifting gillnets were estimated to be killing c. 500,000 birds per year, prior to a UN moratorium in 1992 (DeGange et al., 1993 and Uhlmann et al., 2005). A review by Robins (1991) found 60 species of seabirds had been reported caught in gillnets worldwide, and that net mortality was a major contributor to declines of auk populations in California, Newfoundland, the Canadian Arctic, west Greenland and northern Norway. A regional review revealed that between 100,000 and 200,000 seabirds could be being killed annually in gillnets in the Baltic and North Sea region alone (Žydelis et al., 2009).
Surprisingly, the global magnitude and significance of seabird bycatch in gillnet fisheries remain largely unknown (Robins, 1991 and Žydelis et al., 2009). Assessment is hampered by large and diverse artisanal fisheries (i.e. small-scale fisheries for subsistence or local markets, typically using traditional fishing gears and small boats), and data on fishing effort and catch of target and non-target species are very sparse.
Based on bird feeding ecology we identified 148 seabird species as susceptible to bycatch in gillnets, of which 81 have been recorded caught. The highest densities of susceptible species occur in temperate and sub-polar regions of both hemispheres, with lower densities in tropical regions. Gillnet fisheries are widespread and particularly prevalent in coastal areas. A review of reported bycatch estimates suggests that at least 400,000 birds die in gillnets each year. The highest bycatch has been reported in the Northwest Pacific, Iceland and the Baltic Sea. Species suffering potentially significant impacts of gillnet mortality include common guillemot (Uria aalge), thick-billed guillemot (Uria lomvia), red-throated loon (Gavia stellata), Humboldt penguin (Spheniscus humboldti), Magellanic penguin (Spheniscus magellanicus), yellow-eyed penguin (Megadyptes antipodes), little penguin (Eudyptula minor), greater scaup (Aythya marila) and long-tailed duck (Clangula hyemalis). Although reports of seabird bycatch in gillnets are relatively numerous, the magnitude of this phenomenon is poorly known for all regions. Further, population modelling to assess effects of gillnet bycatch mortality on seabird populations has rarely been feasible and there is a need for further data to advance development of bycatch mitigation measures.
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June 14, 2013