Fishery and bionomics of tunas at Calicut

Fishing operations by drift nets were in vogue off the Malabar region on a medium scale since the beginn. ing of this century. Four types of drift nets operated aboard the canoes or non-mechanised boats were extant since that time ; they were : (1) a thick large-meshed and heavy (325 mm mesh size) hemp drift net locally called ' Sraavu vala' (shark nets) employed for the apture of large sharks, sawfish, billfishes, etc. from deep waters, (2) a thin big-meshed (12-20 cm mesh) hemp drift net called ' Thirandi vala' (Rayfish net) used mainly for the capture of rayfishes, skates and sawfish from the nearshore waters, (3) a small-meshed (7-8.5 cm) cotton-made or hemp drift net called ' Kandadi vala' used for the capture of smaU sized cybiids, Chirocentrus, pomfrets, sharks, sawfish, tachysurids, large carangids and mackerel and, (4) a slightly bigger meshed hemp drift net called ' Odu vala' (9-12 cm mesh) used for the capture of big-sized fishes such as cybiids, tunas, tachysurids, pomfrets, Chirocentrus, carangids, chorinemids, Rachycentron, sphyraenids, and medium-sized sharks