Observed links between coastal ocean processes and Indian Oil Sardine (Sardinella longiceps) fishery along the southwest coast of India

The annual fishery of the Indian Oil Sardine (IOS), Sardinella longiceps, seems to be influenced by the ambient conditions prevailing in the habitats during their early life-history. The present study is aimed at understanding the putative behaviour of IOS along the southwest coast of India (SWCI) to monsoonal upwelling which triggers surface productivity. Mixed layer temperature is observed to be an indicator of the habitat choice and reproductive performance of IOS. A Multi-Criteria Analysis (MCA) model was envisioned to explain the interannual variability of the IOS fishery. In this model, the coactions of variables such as standardized catch per unit effort (SCPUE) of IOS in the first quarter (January to March), southwest monsoonal upwelling index (SWM-UI), and pre-monsoonal mixed layer temperature (PM-MLT) over three decades from 1985 to 2016 were looked upon as indicators to explain the interannual fluctuations in the fishery. Eight different criteria for eight ranks were assigned using reference values for variables. The model ranks the years based on the respective conditions defined based on the suitability criteria for IOS. The model showed a strong relationship of the variables on the annual IOS fishery and revealed that the higher first quarter SCPUE (>3.678) and SWM-UI (>758.7 kg/m/s) influences the interannual variability of the fishery significantly. The primary causative factor for the collapse of this fishery during 1992-99 was the frequent occurrence or co-occurrence of extreme climatic events such as El Niño, La Niña and Indian Ocean Dipole (IOD). Further, a significant increase (p<0.05) in IOS fishery was observed during 2000-07 due to favourable upwelling conditions along the SWCI. The uncertainties prevailing in a complex tropical ecosystem and associated challenges in resolving a multi-craft-gear fishery were addressed using statistical tools to infer logical explanation on the decline and revival of IOS.