Mesh selectivity of net pot for white-spotted conger-eel Conger myriaster in Ise Bay

Abstract

This study estimated the mesh selectivity of net pots for white-spotted conger eel Conger myriaster in Ise Bay in order to reduce the bycatch of conger eel under 250 mm total length, the size limit for landing at fish markets from October and November by the Stock Recovery Plan in Ise and Mikawa Bay. Experimental fishing was carried out 13 times from June 2003 to November 2004 by using six mesh sizes: 12.6, 14.3, 16.1, 17.9, 20.2 and 27.8 mm, and the mesh selectivity master curve was estimated by the SELECT method. The mesh selectivity master curve was estimated to be s(A) = exp (-16.20 + 11.84R)/1 + exp (-16.20 + 11.84R), where R is the ratio of fish girth to mesh size. Total lengths of 50% selection for the six mesh sizes given above were calculated to be 224, 245, 266, 287, 313 and 367 mm, respectively. According to the proportion of conger eel landings of each fish size category at Wakamatsu fish market, conger eel landings of a total length around 300 mm account for about 20% of the total landings. Thus, in order to retain conger eel over 300 mm, returning undersized fish less than 250 mm where possible, and use of net pots with a mesh size of 16.1 mm is considered acceptable for the fishermen in Ise Bay at the present time.