Factors influencing the abundance of Acetes sp. along Gujarat coast: A preliminary analysis

Abstract

The states of Maharashtra and Gujarat together contribute about 24 per cent of the total catches from Indian waters. Unlike the South-West coast where sardines and mackerel, are the major species, the fishery in this region is dominated by fishes higher in the tropic pyramid. More than 80% of the species in the region have Acetes as predominant food in the guts, which shows the ecological significance of Acetes sp. as a link in the ecosystem. The study was taken up to determine the factors that contributed to the abundance of Acetes along the region, which will be an input for satellite based predictions of fishery resources. Fishing experiments were carried out along Veraval and Diu coasts of Gujarat which have targeted fishery for Acetes using Dept. fishing vessel. Physico-chemical parameters were collected simultaneously from the fishing grounds. The catches of Acetes were highest during post-monsoon and the immediate pre-monsoon. A good correlation (r=0.92) was observed between the Acetes catches and the total CPUE of the catches in trawl catches. The abundance of acetes correlated positively with chlorophyll content in water, which could be taken as a proxy for the plankton abundance. To find the optimum range and predict abundance, analysis based on Random Forest classifiers were used. Chlorophyll and temperature were the most important factors that determined the abundance of Acetes. But the major classification was based on the season and the winter season forming another node. The first node could be further divided based on the chlorophyll concentration which was further separated based on the limiting temperature. In the winter season, the abundance is seen to be based on a lower surface temperature at 25.15 degree celsius. A temperature of 27.25 degree celsius limits the production of Acetes sp. and also the factor seasons, which could be the combined effect of circulations. A species distribution model using maximum entropy data was developed, which proved the reason for distribution of Acetes along the northwest coast and also the discontinuous distribution of Acetes reported in literature. The possibility of inclusion of the results of this study, in the potential fishing, for northwest coast using the concentration of chlorophyll, temperature, phosphate and nitrate is discussed in the paper.