By-catch from the Artisanal Shrimp Trawl Fishery off Negombo, Sri Lanka

Abstract

By-catch is one of the serious problems in shrimp trawling. This study analyzes the by-catch of a well-established traditional shrimp trawl fishery that exists in the coastal waters off Negombo, Sri Lanka. Catch, effort data and by-catch samples were collected by making fortnight field visits to the trawl landing site at Negombo from January to December 2019. The total catch (kg) and CPUE (kg hr-1) of shrimp and by-catch, shrimp to by-catch ratio, composition of by-catch and its economic benefits were assessed. By-catch reported lower CPUE values (1.3±0.5 kg hr-1) than shrimp (2.6±0.8 kg hr-1) throughout the study period except in April and July. The estimated shrimp to by-catch ratio in this traditional trawl fishery is 1:0.52. By-catch represents 51 fish species from 17 families, 3 crab species, 2 species of rays and 3 cephalopod species. The total annual by-catch was estimated at 25.55 Mt, which comprised 80% fish, 10% crabs, 3% rays and 7% of other invertebrates. Species belonging to the family Sciaenidae made the highest percentage contribution (26.04%) to the total by-catch followed by Cynoglossidae (15.87%), Clupeidae (11.18%), Pristigasteridae (10.7%) and Leiognathidae (10.51%). By-catch provides livelihoods for fifteen women fish vendors in this area, generating an average daily income of ~1, 069.00 LKR and also makes 8% contribution to the average daily income of a shrimp trawl (~3, 940.00 LKR). There were no reported discards in this fishery. The findings of this study will be useful in updating existing information and defining measures to manage and better utilize by catch in this small-scale fishery.