Can Changing Cod End Mesh Size and Mesh Shape Affect the Nearshore Trawl Fishery off the West Coast of the United States?

Abstract

A study, spanning the years 1988–1990, on the impact of trawl cod end mesh size and mesh shape was undertaken onboard nearshore bottom trawl vessels operating under production conditions off the west coast of the United States. Short-term impacts with experimental cod ends were analyzed. Six cod ends were used as treatments: 76-, 114-, 127-, and 140-mm diamond mesh, and 114- and 127-mm square mesh. Three response variables were used to compare these cod ends: utilized catch weight (weight of marketable-sized fish), size-discard catch weight (weight of fish discarded due to small size), and giller weight (weight of fish wedged between meshes). Species composition differed between the “inner nearshore” area (0–91 m depth) and the “outer nearshore” area (>91–183 m depth). For all cod ends, the inner nearshore had a consistently greater percent total discard than the outer nearshore. The individual cod end results showed that the 76-mm diamond gave excessively high size-discard rates for both areas. The 114-mm square mesh performed well in the outer nearshore, giving high utilized weight per hour and low size-discard weight per hour. The 114-mm diamond mesh did better in the inner nearshore, where a larger percentage of flatfish were utilized, giving a reasonable utilized weight per hour and also a low size-discard weight per hour.