Biology and fishing of bigfin reef squid (Sepioteuthis lessoniana Lesson) by squid trap at Sikao bay Trang province

Study on biology of bigfin reef squid (Sepioteuthis lessoniana Lesson) and its optimum fishing efforts (squid trap) at Sikao Bay, Trang Province was conducted. The data of length, weight, fecundity and number of males and females from 1995 to 1997; and data of catch, fishing efforts, seasonal fishing and fishing method from 1987 to 1997 were collected from fish mongers along the Sikao Bay. The study revealed that the bigfin reef squid can reproduce through out the year which can be divided into 3 periods; i.e.; from the end of November to February, May to early of July and at the end of August to October. The age of first maturity was 3-4 months. After fertilization for a week, the female lay the fertilized eggs that attach to the bottom substrates. The male moves around the female during laying the eggs. The fertilized egg characteristics are tamarind fruit-liked, colony and adhesive. Fecundity was 486-2,186 eggs. The fertilized egg will be hatched out within 2-3 weeks. The size of newly hatched juvenile was 0.5 cm in length and weight 0.1-0.3 gm. The young squid food is small crustaceans and other aquatic animals. Bigfin reef squid mainly caught by squid trap. The trap is set overnight at the depth of water 7-23 m and harvest in the next morning. The fishing grounds are the sea areas around the islands in Sikao Bay. Fishing season is whole year round with the exception of south-west monsoon period. The squid fishery in this area had been overfished since 1991 that resulted to the decreasing of the catches in the following years. However, with the declining of fishing efforts the catches increased again. The study revealed that the bigfin reef squid maximum sustainable yield was 301.69 tons and its optimum fishing effort was 54,000 days. Thus, for the sustainable squid fishery in this area the number of fishermen should be limited to 225.