Shark fishery of Veraval coast with special reference to population dynamics of Scoliodon laticaudus (Muller Andhenle) and Rhizoprionodon acutus (Ruppell)

Abstract

During 1979-81 on an average 823.1 t of sharks were landed in a year which constituted 2.9 % of total marine fish landed. The annual average gearwise catch was 340.4 and 482.7 t by trawl and gill nets respectively. The peak period of abundance of sharks was during December-March as indicated by the catch rate of trawl net and the catch rate of gill net indicates that the abundance was 'good in all the months except in October and November. Among several species of sharks which supported the fishery, Scoliodon laticaudus (Muller and Henle) and Rhizoprionodon acutus (Ruppell) were dominant and constituted on average 43.3 and 31.2% in trawl and gill net catches respectively. Sexwise growth parameters of these two species have been estimated from length frequency data, tobe. Loe680mm, K 1.0822/yearand to—0.0119 for males and Lac 749 mm, K 0.8818/year and t | -f-0.0123 for females of S. laticaudus. the growth parameters of male R, acutus are estimated to be LOG 1054 mm, K 0.6457/year and to —0.0526 and of female Loe 1065 mm, K 0.6046/year and to—0.0556. The growth in weight of both the sexes of these two species are also given. The natural mortality coeflBcient for both sexes of S./la/fcaarftts are 1.76 for males and 1.53 for females and for R. acutus are 1.12 for males and 1.01 for females. The gsarwise estimates of total mortality coefficient have been given for both the sexes of these two spscies. The estimates of age at first capture with regards to different gears have been obtained. The sexwise yield per recruit studies of both the species indicate that both the sexes of 5. laticaudus is not exposed to high fishing intensity and the effort of trawl and gill net may be increased to exploit this spscies more effsctively without further reduction in the age of first capture from the prevailing level. The males of R. acutus are exposed to midsrately higher fishing pressure whereas the females are not. In general, there is scops for the increase in production of these two species by intensifying the effort of trawl and gill net units as the present F are lower than the Fmax of the respective gears and species