Effect of mesh lumen area on girth of fishes and catch in deep sea gill nets operated off Cochin

Abstract

Gill net is one of the most common and a very selective fishing gear used all around the world. A wide range of designs with different hanging ratios are often used in the fishery. The present study compared the effect of different hanging ratios of drift gillnets on catch rates, size composition and catch per unit effort. Maximum girth of fish caught was compared to lumen area of the mesh with reference to different hanging ratios. The experiments were conducted with three drift gillnets of 140 mm mesh size made of polyamide 210x9x3 rigged at three hanging ratios, E equals 0.4, 0.5 and 0.6 respectively. Experiments were conducted onboard FV Sagar Harita at 40-60 m depth off Cochin during September 2016 to February 2017. The major species caught were Scomberomorus commerson, Sphyraena jello, Caranx sp., Rastralliger kanagurta, Parasromateus niger and Istiophorus platypterus. Maximum catch was recorded in nets rigged at 0.5 followed by 0.4 and 0.6 hanging ratio. Among different modes of capture, wedging and entangling and wedging contributed the most to the catch. Maximum girth of three species, R. kanagurta, P. niger and S. commerson werecompared with mesh lumen area. The maximum girth at which P. niger was caught decreased with increase in hanging ratio and the trend was reverse for S. commerson. The relationship was different in case of R. kanagurta, where the maximum girth decreased initially from 0.4 to 0.5 and then increased at 0.6 hanging ratio. Comparing mesh lumen area with maximum girth could be a novel concept for determining optimum size of fishes as per minimum legal size or sustainability is concerned. The results of the finding are discussed in the paper.