Influence of climatic variables on selected marine fish populations in south estern Arabian Sea

Abstract

The potential impacts of climate variables on commercially important marine fish population in the southeastern Arabian Sea are mostly unexplored. There are large knowledge gaps that prevent a comprehensive understanding the impacts of climatic variables from the other factors which influence the fish biomass and catches is vital for studying the stock dynamics of fishery resources. The study used Biomass Dynamic Models to investigate relationships between environmental variables and the biomass of commercially important fish species along southwest coast of India and to predict their future changes under various RCP scenarios. For modeling, the time-series data on species/resource wise, gear-wise annual catch and fishing effort for the harvest of selected fishery resources for the period 1985-2019 were used, along with the environmental variables such as annual average data on Sea Surface Temperature (SST), Coastal Upwelling Index (CUI), Marine Heat Waves (MHW) and precipitation (PPT). The results indicate that the models attempted for all the fish groups gave very good fit as observed by the regression plots of observed catch against expected catch with high regression coefficients. The biomass estimated using the model parameters indicate that, the climate variables considered in the present study showed significant lagged effects on biomass of the fish species in varying intensities. The SST component in the biomass was highest for the pelagic fish species ribbonfishes and the contribution to biomass due to SST ranged from 25.7% to 26.4% with an average of 26.0%, and lowest for squids. In general, the influence of SSST on the biomass of two pelagic species are greater that of the demersal species. The influence of precipitation on the biomass of the fish species selected for study were always lower than that of SST both in pelagic as well as demersal resources. The influence of CUI and MHW were much lower in all the species studied compared to that of SST and precipitation, with MHW became the least influencing variable. The predicted biomass tends to decrease over the future periods in the SST model, and increase for the precipitation along the region. In both the projections, lowest values were observed for RCP 6 and highest values for RCP 8.5 scenario for all the species. Coupled with overexploitation, and habitat degradation, climate change impacts are reported to cause challenges in the sustainability of marine ecosystems and fisheries along the coastal waters of India. Present study throws light on the use of biomass dynamics models to unravel the effects of climate variables on the fish biomass and the results indicate that the dynamics of climate variables should also be taken into consideration while determining the harvestable potential of each fishery resource, especially, for the pelagic fish stocks.