Growth, mortality and population parameters of three cephalopod species, Loligo duvauceli (Orbigny), Sepia aculeata (Orbigny), and Sepiella inermis (Orbigny) from north-west coast of India

Growth, mortality and population parameters of three commercially important cephalopods viz., Loligo duvauceli, Sepia aculeata and Sepiella inermis are reported based on length measurement of 49,960 specimens collected during the period 2001-‘06. The asymptotic length (L∞) was estimated as 380, 300, 108 and 102 mm for L. duvauceli , S. aculeata and S. inermis male and S. inermis female, respectively. The growth coefficient (K) was estimated as 0.90, 0.67 and 1.81 and 1.74 yr-1 for L. duvauceli, S. aculeata and S. inermis male and female, respectively. Highest value of total mortality was recorded for S. inermis female (11.43) and lowest (4.43) for L. duvauceli. The optimum length of capture (Lopt) has been calculated as 139, 150 and 89 mm, whereas, the length of first capture for the three cephalopod species in the same order has been estimated as 100, 95 and 42 mm. The yield isopleths were generated for all the three species to ascertain the potential yield at different levels of Lc/L∞ and E. Major percentage of the catch of these resources is below the length at maturity (Lm) and optimum length of capture (Lopt). All the three species are of high demand in the export market and therefore, some measures need to be taken in order to reduce exploitation of young ones of these species in order to sustain the fishery in future.