Characterization of low value bycatch in trawl fisheries off Karnataka coast, India and its impact on juveniles of commercially important fish species

Abstract

Trawl fishery is a mixed fishery targeting numerous species and sizes simultaneously, and therefore remains a controversial fishing method due to consequential catch of huge amount of non-targeted species. Along with non-commercial species, bycatch also includes commercial species that are below minimum legal size (MLS) or less profitable fishes owing to market conditions. Advanced technologies in fishing methods and fleet infrastructure are being introduced and practiced. Such developments have ensued in heavy exploitation of juveniles of commercially important fishes. Mangaluru fisheries harbour witnessed an average 168 thousand tonnes (t) of trawl landings/year in 2012-14, of which 133 thousand t (79 %) was retained for edible purpose and 0.35 thousand t (21 %) was marked as “low value bycatch” (LVB) which mainly transported as raw material for fish meal production. To assess the sustainability of marine fisheries production, it is important to understand the species composition and the juvenile composition of the fishes in LVB. A total of 121 species of finfishes were recorded from LVB of multiday trawlers (MDT). Among that, commercially important juveniles formed 47.5 % of the finfish LVB by weight (56.1 % by number). An estimated 4,693.4 t (272.4 million by numbers) of Decapterus russelli juveniles, 1,395.7 t (144.9 million by numbers) of Saurida tumbil, 1,671.4 t (142.9 million by numbers) of Rastrelliger kanagurta and 338.3 t (90.1 million by numbers) of Nemipterus randalli were landed as LVB per year by multiday trawlers. From the results it is evident that marine fisheries will be in serious threat in successive years if the similar trend continues. The study strongly advocates LVB management through adoption of Juvenile Fish Excluder-Shrimp Sorting Device (JFE-SSD) and reduced effort in critical fishing grounds would bring down the damages to the marine ecosystems.