Fishery and biological aspects of yellowfin tuna Thunnus albacares along Andhra Coast, India.

A potentially rich fishing ground for yellowfin tuna Thunnus albacares discovered off northern Andhra Pradesh along the east coast of India at depths of 200m and more is being gainfully exploited by the local fishers since 2002. Hooks and lines as well as trolls operated mostly from non-mechanized crafts (catamaran) are the major exploitation methods used. The mechanized sector ventured into oceanic tuna fishing during 2006 with the conversion of a few existing mechanized trawlers into long liners and for large scale commercial exploitation of yellowfin tuna in this region. The average annual (2004-2006) landing of tuna by the catamaran at Visakhapatnam was 1,515t. A wide size group represented the fishery with the fork length of T.albacares measuring from 25 cm to 190 cm with major modes at 90 and 130 cm. Fishes above 80 cm were found to be mature and the size at first maturity was estimated to be between 90-95 cm. Males were dominant with a male: female ratio of 1: 0.58. The length weight relationship is given by the formula W= 0.008634L 3.12. Food contents consisted of a variety of prey animals. Fishes (bony pelagic fishes), crustaceans (crabs and shrimps) and molluscs (squids) were the major prey groups. The fishery is still in its infancy and more research has to be carried out to understand its biology and formulate proper management measures to sustainably harvest this stock.