Studies on population structure, mortality, growth and exploitation level of smooth hammerhead Sphyrna zygaena (L) (Carcharhiniformes - Sphyrnidae) in the coastal region of Kerala, India

The hammerhead sharks (Sphyrnidae), have a circumglobal distribution in tropical and warm-temperate waters, and the smooth hammerhead, Sphryna zygaena is a globally exploited. The current population status of S. zygaena captured from the Kerala coast of Indian Ocean was assessed in terms of yield-per-recruit and biomass-per-recruit analyses during 2008-2009. The growth parameters, asymptotic length (L∞) and growth coefficient (K) were estimated.The von Bertalanffy growth model resulted in growth parameters of L∞ = 362.25 cm and K=0.23 year-1. The average total, natural and fishing mortality coefficients were estimated as 0.35, 1.39 and 1.74 respectively appear to be appropriate for utilization of the stock. The present study reveals that the exploitation ratio of S. zygaena along the Kerala Coast of India is 0.8 and therefore the stock is overexploited. It can be concluded that Sphyrna zygaena is over exploited along the Kerala Coast and proper management steps have to be taken for maintaining the fishing effort of S. zygaena in the Indian ocean so as to result in higher economic yield thereby this fishery operates near biologically optimal level.