The Effect of Net Colour on the Catch Efficiency of Gillnets Operated in Vembanad Lake, Kerala, India

Abstract

Gillnets are commonly used in inland lakes due to their simplicity in construction and operation, efficiency, and low energy usage. The Vembanad lake is one of the most prominent lakes in Kerala, contributing significantly to the small-scale and artisanal fisheries, in which gillnets are the predominant gear. There have been studies on the effect of gillnet panel colour on the selective capture of fish species, primarily in the open ocean and rivers. Although a considerable number of studies exist on the species profile and fish catching methods in the lake, the efficiency of coloured webbing for gillnets is not available. The efficiency of coloured webbing for gillnets is not documented, which, if available, would be a crucial input for implementing gearbased technical measures for conservation in gillnets in the lake. In this regard, a study was conducted along Vembanad lake and the lower reaches of the Muvattupuzha river to compare the catch efficiency and species profile of transparent gillnets typically employed in the region with gillnets fabricated using blue and green coloured webbing. The results demonstrated a considerable increase in CPUE for green-coloured gillnets (708.9±12.8 grams per operation) compared to blue and transparent gillnets, which had CPUE values of 397.9±80.2 and 293.7±70.6 grams per operation, respectively. Significantly higher catches of Horabagrus brachysoma and Etroplus suratensis were obtained with the green-coloured gillnets than with the control (Transparent). Lengthwise data showed that green-coloured nets captured larger individuals of E. suratensis, but significant difference was not observed in other species. The number of E. suratensis captured in each gillnet contributed to the most dissimilarity in all comparisons, followed by Gerres sp. and H. brachysoma, according to similarities percentage analysis conducted to comprehend the species assemblage structure. This is the first report on the effect of gillnet colour on the catch efficiency of gillnets in Vembanad lake, and the results, which indicate species-specific differences in capture, will be one of the many inputs necessary for implementing gear-based technical measures in the gillnet fishery in the lake.