Insight on the reproductive biology of small striped cuttlefish, Sepia prabahari in Gulf of Mannar, Indian Ocean and recommendation for a minimum legal size

Abstract

This paper provides insight into the size composition and reproductive aspects of small striped cuttlefish Sepia prabahari distributed exclusively in the Gulf of Mannar (GoM) Biosphere Reserve, in the Indian Ocean which contributes 11% to the cephalopod catch in this region. The size composition in the fishery varied between 4.6 and 14.6 cm in dorsal mantle length (DML) and the length group between 8.1 and 10 cm dominated the catch (45%). The DML-weight relationship for male, female and for the pooled sexes were 0.5561 DML2.31; 0.4821 DML2.39 and 0.5214 DML2.34 respectively. Observations on maturity stages indicated year-round spawning with two peaks. Maturity indices increased in tandem with the gonadal development in the cuttlefish. Mean GSI in females showed a multi-fold increase from 0.41 in maturing to 2.20 in mature stages, while it increased from 0.51 to 1.35 for the respective stages in males. The minimum legal size (MLS) was set considering the minimum size at maturity of 7.0 cm for the species. The Lm50 estimated at 9.2 cm DML for males; 9.7 cm for females and 9.4 cm for the pooled sexes, showed early maturation in males. The size composition indicated that nearly 53.7% of the commercial catch in the fishery is below the Lm50, while 5% of the catch was below MLS. Management measures limiting the fishing pressure on sub-adults are recommended for sustainable exploitation of the resource.