Fishery and population dynamics of Trichiurus lepturus (Linnaeus)off Veraval, north-west coast of India

The fishery and population dynamics of Trichiurus lepturus (Linnaeus) from Veraval was studied for the period 2003-2006. The average annual catch was 18,813 t, forming 27.63% of the total trawl catches at Veraval. September to December was the most productive period in terms of catch and catch rate. The length-weight relationship showed that growth was allometric and there was no significant variation between the sexes. The growth parameters L- and K were 134.1 cm and 0.29 respectively and the length attained at the end of 1, 2, 3, 4 and 5 years were 35.28, 60.16, 78.77, 92.70 and 103.12 cm respectively. The growth performance index (o) was 3.717 and longevity was 10.29 years. Recruitment pattern was trimodal with two major peaks during May - June and August -October and one minor peak during January - March and the length at first capture was 14.11 cm. The natural mortality, fishing mortality and total mortality were 0.51, 0.93 and 1.44 respectively and exploitation ratio was 0.64. The maximum sustainable yield was 14,565 t which was lower than the average annual catch indicating over-exploitation of the species. The yield per recruit and biomass per recruit was 43.34 g and 46.6 g respectively and increase in relative yield by 142.41% would be obtained by decreasing the present level of fishing by 60%.