Reproductive biology of Pharaoh cuttlefish Sepia pharaonis Ehrenberg, 1831 along the Gujarat coast, India

Gujarat is a leading maritime state in the production of marine finfish and cephalopods in India. The cephalopods are one of the major fishery resources along the region having a good domestic and export demand. These resources are exploited majorly by bottom trawls along the region. Sepia pharaonis contributes nearly 20 % to the cephalopod landings of Gujarat. However, the fishery and reproductive biology of the cephalopod, Sepia pharaonis is poorly known from the region. The specimens for biological analysis along with fishing operations and fishing data using a structured questionnaire were collected from the multi-day trawlers based at the Veraval Fishing Harbour for the period of 2017 – 18. The maximum observed length (Dorsal Mantle Length (DML)) among all specimens was 361 mm with a mean DML of 239.52 mm (sample range DML). Sex ratio revealed that the males are dominant over the females (M: F = 1:0.75) in the catch composition. The size at first maturity was observed at 213.1 mm DML, which is lower than the mean size of the fishery. The month-wise significant variations (p < 0.05) were observed in the values of GSI and NSI during the study period and peak values indicate the spawning season of the fishery. The proportion of maturity stages in different months as well as maturity indices indicates perennial spawning season with peak spawning activity during December – March months. The ova diameter studies revealed ovum sizes from 0.99 – 14.30 mm (6.52±3.35). The fecundity varied from 1,358 – 6,005 ova (average = 2,883). The current research study is the maiden attempt along the region and further supports the formulation of management plans for the sustainable exploitation of the resource