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The landings of Indian oil sardine (Sardinella longiceps, Clupeidae) along the south‐eastern Arabian Sea are about 43.8% of total Indian oil sardine production. The annual landings of this species exhibit large‐scale variability with prolonged years of surplus or deficit landings without identified reason. Evaluating Indian oil sardine landings along the Kerala coast during 1961–2017 in relation to environmental variations, we have elucidated a putative link between variability in landings versus environmental parameters and climate indices. The variables examined in this study, such as salinity and temperature along with physical indices such as upwelling and mixed layer depth (MLD) of the ocean help to propose a mechanism to temporal variability in the landings of Indian oil sardine. Colder temperature and timely intense upwelling lead to nutrient enrichment in the surface water, which promotes the growth of phytoplankton (chl‐a) and thereby food availability to Indian oil sardine are found during years with surplus catch. Less saline surface waters and shoaling of MLD at these times could lead to the aggregation of fish at particular depths and thereby a good catches. The reverse mechanism, such as more surface saline water, warm temperature, downwelling or weak upwelling, and less nutrient enrichment, leads to deficit landings. Further, it was noticed that the Pacific decadal oscillation and Atlantic multidecadal oscillation have a more pronounced impact on Indian oil sardine landings over the coast of south‐eastern Arabian Sea than previously reported ENSO associated impacts. All these point towards climate change implications for the Indian oil sardine fishery. [ABSTRACT FROM AUTHOR]

An attempt has been made to develop a holistic understanding of upwelling and downwelling along the south-west coast of India. The main objective was to elucidate the roles of different forcings involved in the vertical motion along this coast. The south-west coast of India was characterized by upwelling during the south-west monsoon (May to September) and by downwelling during the north-east monsoon and winter (November to February). The average vertical velocity calculated along the south-west coast from the vertical shift of the 26 °C isotherm is 0.57 m/day during upwelling and 0.698 m/day during downwelling. It was concluded that upwelling along the south-west coast of India is driven by offshore Ekman transport due to the alongshore wind, Ekman pumping, horizontal divergence of currents and by the propagation of coastally trapped waves. Whereas downwelling along the coast is driven only by convergence of currents and the propagation of coastally trapped Kelvin waves. Along the west coast of India, the downwelling-favorable Kelvin waves come from the equator and upwelling-favorable waves come from the Gulf of Mannar region. [ABSTRACT FROM AUTHOR]

The landing of Indian oil sardines, Sardinella longiceps Valenciennes, 1847, along the southwest coast of India is highly variable. A few physical parameters and processes correlated with sardine landing could not establish a flawless connection and explain the phenomena of interannual variability. Earlier research has indicated that the probable appearance and disappearance of sardines is an active movement in search of food and favourable conditions. But no specific study has been carried out to explain the variability of sardine catch based on chlorophyll availability on a synoptic scale. An attempt is made in this study to correlate variability in chlorophyll a with sardine landings along the waters of the southwest coast of India. We have estimated monthly averaged surface phytoplankton biomass along the waters of the southwest coast of India from the shoreline up to the 200-m isobath for 10 years from SeaWiFS ocean-colour data. This estimation is compared with the biological calendar of Indian oil sardines. The average chlorophyll a for the bloom initiation month (1998-2006) matches very well with oil sardine landings. The results imply that the concentration of chlorophyll during the bloom initiation month can be used to assess the quantity of fish that recruit into the population. Finer scale spatial variations in the chlorophyll along the coastal waters help in deciphering the migratory pattern of sardines during their active breeding phase. This study shows that 39% of interannual variability in fish landings is related to availability of chlorophyll a during the bloom initiation month. [ABSTRACT FROM AUTHOR]

Mudbanks, a unique coastal oceanographic phenomenon occurring along the southwest (SW) coast of India during the SW monsoon season, are synonymous with the fishery of this region. Here we examine the validity of the popular notion that mudbanks directly support rich fisheries, using a high temporal resolution water column data collected from the Alappuzha mudbank region in Kerala during April to September 2014, in conjunction with fisheries data. Our study reveals that the upwelling which occurs during the SW monsoon season along this coast brings oxygendeficient subsurface water to the upper water column. Escaping the oxygen-depleted waters, the fish aggregate within a thin upper layer allowing easy visual identification and capture of fish shoals. This process occurs throughout the coast and is not confined just to the mudbanks. Mudbank being a calm region, traditional fishermen using non-motorized country craft were able to carry out fishing within this region only during the SW monsoon. With the induction of motorized and mechanized fishing, the link between mudbanks and fisheries is becoming less prominent, although the former still continue to be important fish landing centres. [ABSTRACT FROM AUTHOR]