Fishery, reproductive biology and stock status of the largehead hairtail Trichiurus lepturus Linnaeus, 1758 off Karnataka, south-west coast of India

Ribbonfish fishery along Karnataka Coast is supported by a single species, the largehead hairtail Trichiurus lepturus. The species is exploited mainly by trawls and gillnets and during 2007-2012, production from Karnataka fluctuated between 11090 and 28845 t. The asymptotic length (L∞), growth coefficient (K) and age at zero length (t0) for T. lepturus were estimated as 116.75, 0.65 yr-1 and -0.171 respectively. Recruitment showed a bimodal pattern with peaks during March to June and August to December. Total mortality, fishing mortality and natural mortality were estimated at 3.32 yr-1, 2.41 yr-1 and 0.91 yr-1 respectively. The length at first capture (L50) and size at first maturity (Lm50%) were estimated at 54.91 cm and 55.4 cm respectively. Mean length in the catch was 67cm indicating that the fishery was sustained by mature fishes. However, the current exploitation rate (E) is 0.73 which is little higher than E0.1 (0.70). As ribbonfish is an r selected, tropical species with a very high fecundity, SSB of 20% would help to maintain the fishery at sustainable levels and hence it is advisable to reduce the effort by 20%. Thompson and Bell bioeconomic analysis showed that the present level of exploitation can maintain the revenue from the fishery at economic level.