Modification of trap nets to reduce capture of common loons

Abstract

All state licensed commercial fisheries taking lake whitefish (Coregonus clupeaformis) in Michigan waters of Lake Superior have been required to use trap nets since 1974. Trap nets are fished with pot depths (≤27.4 m (90 ft), which is within easy reach of deep diving common loons (Gavia immer). In 1993, some commercial fisheries began to modify (increase) the mesh size on the top of the net heart from 20.4 cm (8 in) stretched mesh to 30.4 cm (12 in) stretched mesh to allow loons to escape. In 1995, 3 fisheries were monitored to estimate catch and mortality of common loons. These samples represented 9% of the total annual trap net effort by these fisheries. Seven dead loons were found entangled both in the pots and in the hearts. None was caught in the heart of modified nets. The extrapolated annual catch of common loons was 77, with 43% of these caught in the hearts of unmodified nets, compared to 86% in unmodified nets before conversion. It appears that stretched mesh size of 30.4 cm reduces catch and mortality of common loons, thus a recommendation to convert tops of nets to large mesh is appropriate. © 1997 Taylor & Francis Group, LLC.