Selectivity estimates for Sepiella inermis (Van Hasselt, 1835) in 40 mm diamond mesh codend trawl net

Abstract

Cephalopods are mostly targeted by trawlers and Sepiella inermis (spineless cuttlefish), contributes about 2 - 4 percent of total cephalopod landings in India. Cephalopods accounted for 6.9 percent of total landings in Gujarat in 2018, with S. inermis accounting for approximately 1 %. The most common length of this species in the fishery is between 35 mm to 147 mm. The length at first sexual maturity varies along the coast, and recent estimates for west coast of India for this species is 48 and 55 mm for males and females, respectively. There are no estimates of trawl codend selectivity for this species and experiments were carried out using a 40 mm diamond mesh codend using covered codend method. The selection parameters for S. inermis were derived using SELECT methodology and the length at 50 % retention (L50) plus or minus(s.e.) was worked out as 36.2 plus or minus 1.2 mm and selection range as 19.9 plus or minus 2.1 mm. The selection factor and the selection ratio for the codend were worked out as 0.9 and 0.55, respectively. The suggested mesh size for the codend based on length at first sexual maturity (LFM) of females (55 mm) and males (48 mm) were estimated as 60 and 53 mm (diamond mesh), respectively. This is the first estimate of trawl selection for this species and operational parameters like towing speed, codend catch etc., that could influence selectivity were not considered and hence more studies by incorporating these factors will help in further refining the parameters of the selection curve.