Fisheries and Biology of Oil sardine, Sardinella longiceps (Valenciennes) and Indian mackerel, Rastrelliger kanagurta (Cuvier) from Kochi and Chennai coasts

The oil sardine Sardinella longiceps and the Indian mackerel \nRastrelliger kanagurta are tropical coastal and small pelagic fish, forming massive \nfisheries in India. They are governed by the vagaries of ocean climatic conditions. \nUntil the mid 1980s, the oil sardine formed fishery almost exclusively along \nsouthwest coast, and did not form fishery along southeast coast. However oil \nsardine emerged as a major fishery in the last 30 years, and the average annual \ncatch along Tamil Nadu coast alone recorded more than 1 lakh tonnes in the last \nfive years. The Indian mackerel also formed a major fishery along southwest \ncoast and a minor fishery along southeast coast. Similar to the oil sardine, the \nmackerel also is contributing a major fishery in the last 30 years along the southeast \ncoast. It is not clear whether stocks of Sardinella longiceps and Rastrelliger \nkanagurta in the two regions are the same, and how similar or dissimilar is their \nspawning and diet. To understand this, samples of the two species were collected \nfrom Kochi (representing the southwest coast) and Chennai (representing the \nsoutheast coast). The study has attempted a comparison between the fishery as \nwell as biological parameters namely morphometrics, maturity patterns, diet \ncomposition of the two species along the Kochi and Chennai coasts during 2010- \n2012. The study revealed that there has been considerable increase in the landings \nof both the species along Kochi and Chennai coasts especially from the mechanised \nsector when compared to previous years. The analysis of morphometric characters \nshowed that Sardinella longiceps and Rastrelliger kanagurta occurring along Kochi \nand Chennai coasts belong to a single stock. S. longiceps of both the coasts \nspawns once in a year lasting from June to September. The peak spawning period \nof R. kanagurta along Kochi was during June-August and along Chennai, during \nApril-June. The length at first maturity \nof mackerel showed much variation during \nthe period and was lower than that reported during the period prior to the 90s. \nThe absolute fecundity was within the range of 4,072-63,475 and 10,116-1, 84,350 \neggs in the case of S. longiceps and R. kanagurta respectively along both the \ncoasts. The diet of S. longiceps consisted of phytoplankton as the major share in \nboth the coasts, and the major phytoplankton species in the diet were almost \nthe same. The diet of R. kanagurta was much diverse with phytoplankton and \nzooplankton, and in this species too, the major species in the diet were almost \nthe same in the two locations. From the results obtained in the present study, no \nsignificant differences could be observed in the spawning and diet composition \nwithin each of the two species between the two locations. The results further \nshow that the two species have adapted to the conditions and have established \ntheir populations along the southeast coast of India.