The consequences of an increase in mesh size in the Irish Sea Nephrops fishery: an experimental approach

Abstract

The result of increasing the mesh size of Nephrops trawls in the Irish Sea from 70 to 80 mm (inside-mesh) throughout was investigated. The controlled variables were fishing method (twin-trawl and parallel-trawls) and diameter of twine used in the construction of the cod-end of the 80 mm net (parallel-hauls only). Significant reductions in catch-rate of Nephrops of 26% and 34% were recorded during 31 twin-trawl and 33 parallel-hauls tows when mesh size was increased to 80 mm with all other aspects of net construction remaining the same. The effects due to fishing method were not significant at the sampling levels attained. The diameter of the cod-end twine was a significant factor at the 10% error level in the parallel-hauls experiment. An increase in diameter from 4 to 6 mm in the 80 mm cod-end resulted in catch rates 20% lower than the 70 mm cod-end with 4 mm twine, compared with 34% when both cod-ends were constructed in 4 mm twine.