Fishery, population characteristics and yield estimates of coastal tunas at Veraval

Abstract

The fishery, population characteristics and yield estimates of coastal tunas Thunnus tonggol, Euthynnus affinis and Auxis
thazard at Veraval were studied during 2003 – 2006. The average annual catch was 731 t, which contributed to 28% to the
total gillnet catches. The main species of tunas landed were T. tonggol (46.8%), E. affinis (17.5%), Thunnus albacares
(6.4%) and A. thazard (5.2%). E. affinis and A. thazard exhibited isometric growth but for T. tonggol it was allometric. The
von Bertalanffy growth equation was Lt = 107.4 [1 – e - 0.18 (t + 0.0729)] for T. tonggol, Lt = 72.5 [1 – e - 0.56 (t + 0.0327)] for E. affinis and
Lt = 46.6 [1 – e - 0.93 (t + 0.0153)] for A. thazard. The mortality rates M, F and Z for T. tonggol were 0.4, 0.72 and 1.12 respectively,
while for E. affinis and A. thazard, the values were 0.94, 1.48 and 0.75 and 4.49, 1.69 and 5.97, respectively. The exploitation
ratios for T. tonggol, E. affinis and A. thazard were 0.64, 0.44 and 0.75 respectively. The higher exploitation rate and lower
MSY in T. tonggol and A. thazard was an indication of intensive fishing and overexploitation of these speceis. But for
E. affinis, the exploitation rate was low and MSY was high indicating further scope for exploitation. Reducing the present
fishing effort by 40%, maximum relative yield was realized for T. tonggol and A. thazard but for E. affinis, increasing the
fishing effort by 80% provided the maximum relative yield.