Assessment of low value bycatch and its application for management of trawl fisheries

Abstract

estimated annual average catch by trawlers operating from Mangalore Fisheries Harbour (southwest coast of India) was 124,105 tonnes during 2008-2011. Of the total catch, 63.9% was landed as high-value catch (HVC) for human consumption, 14.7% as low-value bycatch (LVB), and 11.4% was discarded at sea. However, during the four years, the contribution of LVB to the trawl catch substantially increased from 2.5% to 24.6%; and the discards reduced from 18.1% to 5.9%. As demand for raw material from fish meal plants is increasing, trawlers are encouraged to target LVB. Trawl bycatch consisted of 205 species/groups, of which 147 were finfishes, 4 bivalves, 7 cephalopods, 21 crabs, 3 stomatopods, 3 lobsters and several miscellaneous groups. About 34% of the LVB by weight and 63% by number were juveniles of 45 commercially important species. Mapping spatio-temporal abundances of juveniles of four important demersal fish species showed that the distributions of juveniles occurred along vast coastal stretches for several months in a year. Exploitation of large quantities of juvenile and sub-adult fishes potentially contributes to growth overfishing, reduced economic returns to fisheries and loss of biodiversity; and therefore threatens the sustainable exploitation of resources. A few potential management options such as the use of bycatch reduction devices, spatial and temporal closures to trawling and fisheries refugia are discussed. Assessing the net economic value of benefits and losses due to LVB is required to achieve sustainable management of trawl fisheries.