Fishery and stock assessment of Portunus sanguinolentus (Herbst) from south Karnataka coast, India

Abstract

The study on the exploited fishery of Portunus sanguinolentus off south Karnataka coast during 1998- 2005, revealed that it contributed to 46% of the average annual crab landing with peak in May. The carapace width (CW) varied from 61 to170 mm in males and 56 to 160 mm in females. Percentage of females in advanced maturity stage was high during January-March. Size at maturity of females was 90 mm (CW). Carapace width-weight relationship indicated that males are heavier than females and the growth is positive isometric. The longevity of the species was estimated as 2 ½ years and males and females reach 137 mm (CW) at the end of the first year and 163 mm (CW) in two years. Females reached sexual maturity in 6 months. L∞ and K were estimated as 175 mm and 1.7 year-1 respectively. The estimated total mortality coefficient (Z) was 7.15 and fishing mortality coefficient (F) 4.18. The exploitation ratio (E) was 0.58. Size at capture (L50) was 79.2 mm. Estimated total stock was 852 t standing stock was 118 t and the MSY was 544 t. An increase in fishing effort by 10 to 20 % may enhance the catch only by 3 to 4%. It is suggested that for sustaining the fishery, the fishing effort (in hours) may be reduced by 30 to 40% from the present level of exploitation.