1National Research Institute of Fisheries Engineering, Fisheries Research Agency, Kamisu, Ibaraki 314-0408, 2Choshi Marine Industries Office, Choshi, Chiba 288-0001, Japan
A parallel haul experiment of two trawl nets equipped with groundropes of different diameters was carried out to understand the role of the groundrope for fishing gear selectivity. The diameter of the groundrope of the test net was 61.3 mm on average, while that of the conventional (control) net was 32.7 mm. The selectivity curve of the test net for each species was estimated with an extended SELECT model. The selectivity curve showed a common S-shape for cinnamon flounder Pseudorhombus cinnamoneus and john dory Zeus faber. On the other hand, selectivity curves for red tongue sole Cynoglossus joyneri and black cow tongue Paraplagusia japonica indicated a negative S-shape, as larger individuals escaped from the test net. The test net was non size-selective for bluefin searobin Chelidonochthys spinosus. We considered that these selectivities were based on the species and size dependent behavior to the approaching groundrope. A change in the diameter of the groundrope can be a substantial gear modification for selective fishing in multi-species trawl fisheries.