Impact of El Nino and La Nina on selected commercially important marine fishery resourced of Kerala

Abstract

The El Nino Southern Oscillation (ENSO) is one of the most important coupled ocean-atmospheric phenomenon that causes global climate variability on inter annual time scales. El Nino has become very visible in recent years as a dominant source of inter annual climate variability around the world and will stay as the dominant mode of interannual climate variability with great influence on human populations and ecosystems. ENSO episodes are known to change the environmental characteristics of coastal waters which are the major habitats of the fish resources which are harvested all along the Indian coasts. The impact of diverse ENSO events during 2007-2018 on the marine fisheries of Kerala were studied. The monthly catch of major pelagic and demersal fishes like oil sardine, Indian mackerel, anchovy, penaeid prawns, and threadfin breams by major gears for the period 2007-2018 were collected and catch per unit effort (CPUE) were estimated. The ENSO indices like EMI, MEI, SOL, TNI, Nino4, Nino 1+2 and DMI and ocean-atmospheric parameters such as sea surface temperature (SST), rainfall (RF), chlorophyll a (CHL_A), local temperature anomaly (LTA), salinity (SALT), sea surface height anomaly (SSHA), and ocean current velocity (OCV) were analysed. The relationship of ENSO and those ocean-atmospheric parameters to variations in abundance of oil sardine, Indian mackerel, anchovy, penaeid prawns and threadfin breams were explored with Generalized Additive Model. The GAM results indicated that The ENSO could explain 62.2% of the deviance in the local temperature anomaly (R2.adj=0.56), 59.9% of the deviance in the monthly rainfall (R2. Adj=0.53), 57.9% of the deviance in the sea surface height anomaly (R2.adj=0.52), 52.9% of the deviance in the chlorophyll a concentration (R2.adj=0.45), and 36.9% of the deviance in sea surface temperature (R2.adj=0.30). The ENSO episodes could also explain 31.4% deviance in the abundance of oil sardine (R2.adj=0.25), 31.7% of the deviance in abundance of Indian mackerel (R2.adj=0.25), and 49% of the deviance in the abundance of anchovy (R2.adj=0.39). The study also indicated that a combination of ENSO indices and ocean-atmospheric parameters could explain better the deviance in the abundance of fish resources. The combined model explained 40.1% deviance of oil sardine (R2.adj=0.32), 84% deviance of Indian mackerel (R2.adj=0.75), 71.1% deviance of anchovy (R2.adj=0.58), 58.7% deviance of penaeid prawns (R2.adj=0.5), and 81.2% deviance of threadfin breams (R2.adj=0.7). The ENSO episodes alone could explain 43.6% deviance (R2.adj=0.38) and a combination of ENSO and ocean-atmospheric parameters could explain 71.7% of the deviance (R2.adj=0.63) in the abundance of total fish resources the over the Kerala coast