Bycatch of wintering common and red-throated loons in gillnets off the USA Atlantic coast, 1996–2007

Abstract

Common loons Gavia immer and red-throated loons G. stellata winter along the USA Atlantic coast, where fisheries observers have documented interactions with commercial fishing oper- ations, largely coastal gillnets. The red-throated loon is a conservation priority for the US Fish and Wildlife Service, so interest lies in gauging fisheries bycatch relative to population levels. Gillnet fish- eries observer data from 1996 to 2007 were used in developing generalized linear models to predict common and red-throated loon bycatch rates and investigate gear characteristics associated with high bycatch rates. The predicted bycatch rates were applied to commercial gillnet effort data to estimate total bycatch during this time period. Bycatch was then compared to a potential biological removal (PBR) measure that was calculated from limited demographic parameters. Factors most commonly associated with the bycatch rates were bottom depth and sea surface temperature. Common loon bycatch rates were higher for strings without spacing between nets versus strings with spacing, and for strings that fished ≥24 h versus strings that fished <24 h. Average annual bycatch was 74 (95% CI: 29-189) common loons in the Northeast, and 477 (370-615) common loons and 897 (620-1297) red- throated loons in the Mid-Atlantic. The average red-throated loon bycatch reached about 60% of the PBR measure. This estimated level of bycatch emphasizes that the red-throated loon is a conservation priority, especially considering the unknown level of bycatch in non-oceanic coastal gillnet fisheries and uncertain demographic parameters.