Population Characteristics of Common Murres and Rhinoceros Auklets Entangled in Gillnets in Puget Sound, Washington, from 1993 to 1994

Abstract

Common murres, Uria aalge, and rhinoceros auklets, Cerorhinca monocerata, were the 2 species entangled most frequently in sockeye and chum salmon gillnets in northern and central Puget Sound, Washington, in 1993 and 1994; they comprised more than 90% of all entangled seabirds. The ratio of entangled murres to auklets decreased about 5-fold from approximately 10:1 in 1993 to 2:1 in 1994. Most murres (63%) entangled were adults, whereas most auklets (63%) entangled were hatch-year birds. No significant differences in sex ratio could be detected among age classes of these species within or between fisheries (sockeye versus chum) or years, nor did observed sex ratios deviate significantly from an expected 1:1 sex ratio. During the sockeye fishery (early July through early September), 52% of subadult and adult murres were in breeding plumage, whereas 46% had begun molting flight feathers; by the chum fishery (late September through late November), only 18% were still molting flight feathers, whereas 77% had completed molting their flight feathers. All auklets were in breeding plumage having not yet begun flight-feather molt. No adult murres had visible incubation patches during the sockeye fishery. Because murres fledge from Oregon colonies at least a month earlier than they do from Washington colonies, adult murres from Oregon grow their incubation patches back at least a month earlier as well; this suggests that at least some entangled adult murres came from Oregon. Similarly, some hatch-year murres were entangled in Puget Sound before murre chicks fledged from Washington (or more northerly) colonies, again indicating that at least some hatchyear murres fledged from Oregon colonies.