Stock assessment of Sepiella inermis (Orbigny, 1848) from Mumbai waters

Abstract

The catch of Sepiella inermis landed at New Ferry Wharf contributed about 6.1% to the cephalopod landings during 2001-2003 and the catch rate of the species decreased from 0.26 kg/hr in 2001 to 0.08 kg/hr in 2003. The fishery was supported mainly by the size-range (dorsal mantle length) 40-50 mm for males and 40-60 mm for females. The K and L∞ estimated by Gulland-Holt Plot were 2.63 year-1 and 68.0 mm for males, and 2.35 year-1 and 97.4 mm for females respectively. Males attain 49.74 mm and 63.10 mm and females attain 67.32 mm and 88.11 mm at the end of 6 and 12 months respectively. The total mortality coefficient (Z), natural mortality (M) and fishing mortality (F) was 7.48, 5.09 and 2.39 for males, and 10.78, 4.28 and 6.50 for females respectively. Length at capture (L50) for males is 41.8 mm at an age 4.4 months and the same for the females is 43.9 mm at an age of 3.1 months. Thompson and Bell estimates suggest that to achieve the MEY level the fishing effort has to be increased two-fold. Increasing the effort would not be economically viable and it is also detrimental to the stock. Thus the present level of fishing effort seems to be appropriate.