Trawl fishery of juvenile fishes along Mangalore-Malpe Coast of Karnataka and its impact on fish stock

The article presents the quantitative and seasonal variation in percentage of juveniles in the commercial trawl fishery of Mangalore and Malpe in 2006 and discusses the possible impacts of juvenile fish fishery on fish stock in terms of quantity and value. Twenty finfishes and five shellfishes were identified in which considerable quantity of juveniles were caught, and the juvenile fishery is making notable impact on adult fishery. To understand the impact of the fishery of juveniles in a holistic manner, the species of juveniles caught by trawlers are categorized into three groups: I) both juveniles and adults are caught mainly by trawls II) juveniles of the species are caught in trawl, whereas their adults are targeted by gears other than trawl and III) juveniles of the species are caught by trawls regularly, but their adults are rarely caught or not figured in the fishery of the region. Detailed studies on the length-frequency distribution of important species were carried out to find juvenile percentage by weight, number, and months of abundance of juveniles. By statistical analysis (Thompson and Bell model), possible gain in weight and value of the resources, if the juveniles are not caught by trawls, was projected in category I and category II. In category I, the projection is made based on data available on Nemipterus mesoprion and the study shows that 7% increase in weight and 22% increase in value (286 lakh rupees) can be obtained if the juveniles of this species are not caught. In category II, Scomberomorus commerson is considered as an example for projection. Because the landings of the species by trawlers during 2006 was entirely formed of immature fishes, if the trawl avoids catching these juveniles, 20% increase in yield and 29% increase in value (406 lakh rupees) from the present level is projected by the study. The present article with these examples demonstrates the impact of juvenile fishery on the fish stock and fishery economy of the coast and concludes that since peak periods of specieswise juvenile exploitation is identified, by integrating these temporal data with the spatial data of juvenile fishery, management measures can be formulated and suggested so as to minimize the damages occurring to the commercial fishery due to juvenile exploitation.