Seasonal abundance of small sized juvenile Rastrelliger kanagurta at Vizhingam during 1960-1963

Abstract

The Indian mackerel, Rastrelliger kanagurta (Cuvier) occur in good numbers along the east and west coast of India and is one of the most important commercial fishes in Indian waters. Much of the research was done on the west coast, where there is a considerable fishery for the mackerel. As in most pelagic fishes there have been tremendous variations in yield. Catch in one area of the coast has often differed markedly from that in other areas in the same season, and periods of abundance have been followed by periods of scarcity. This report presents a comprehensive picture of the seasonal abundance and general biology of small sized juvenile mackerel based on observations made at Vizhingam, the southern most centre in the 'mackerel zone' of the west coast of India during 1960-63. The study serves as a basis for fixing the spawning season and spawning periodicity of the Indian mackerel. Appearance of shoals of juvenile mackerel in the inshore fishing grounds is discussed in relation to the prevailing water temperature. Quantitative data on seasonal abundance of juveniles may help in understanding the success or failure of particular year classes and thus in finding reasons for fluctuations in abundance and in developing ways to control the fluctuations. Fishable stocks of mackerel during certain years have become depleted by the fishery to a point where the annual production is well below what it could be, had the small sized juveniles been allowed to grow. An attempt is made to evaluate the detrimental effect of large scale fishing of small sized juveniles when they enter into the fishing grounds. Brief observations on older fish sampled throughout the year are also included.