Length-Girth Relationships of Selected Trawl Resources of Cochin Coast, Kerala

Abstract

Trawling is a major fishing method which contributes significantly to the marine catches of India. Among the many negative impacts that are attributed to trawling, generation of bycatch is the most significant and different technical measures have been adopted world over to reduce bycatch during trawling operations. The optimum mesh size for a technical device is determined by conducting selectivity experiments using different methods, in which length is the main criteria for analysis. However, fish retention in the codend is primarily decided by the girth rather than length, which is often difficult to measure in field and hence length is taken as a proxy for girth. Knowledge of the length-girth relationships of major species would be an additional input for designing gears and deriving an optimum mesh size/shape for trawl codends. The length-girth relationships of 15 commercially important species targeted by trawls along Cochin coast were derived. The results indicated that thirteen of these species had no significant variation in the value of slope, whereas for Pampus argenteus and Trichiurus lepturus, the values for the slope, differed significantly (p<0.05, t-test) indicating that the mesh size requirement would be different for these species. Though estimates did not consider the sex or condition of the fishes studied, the results of the study will be an added input for deriving selectivity estimates.