Fishery and biology of Paphia malabarica (Dilwyn, 1817) off Karapad Bay, south-east coast of India

Abstract

The fishery, biology, growth and mortality of the short neck clam Paphia malabarica (Dilwyn, 1817) was studied from Karapad Bay of Thoothukudi District from January 2013 to December 2019. The annual exploitation of P. malabarica in this bay was between 7.5 t (2016) and 82.5 t (2019) with an average of 22.3 t. The average catch per unit effort (CPUE) was estimated as 17.5 kg person-1 day-1. The male clams were dominant in most of the months except during March, June and October. Chi-square test indicated that, the sex ratio between males and females (1:0.9) was not significantly different. The size at first maturity (Lm) was estimated as 21 mm for P. malabarica in this bay. High percentage (>65%) of mature females was observed between September and December and this pattern suggests spawning season during this period with peak spawning during November. The clam size in the fishery ranged between 24.2 and 55.4 mm (average 39.3 mm) and around 75% of the total catch belonged to 33-41 mm size group. The asymptotic length (L∞) and growth coefficient (K) were estimated as 55.6 mm and 1.1 respectively. P. malabarica attained a length of 37, 49.5 and 53.5 mm at first, second and third year respectively. The tmax was found to be 2.7 year and the growth performance index (Ø’) was found to be 1.53. Total mortality (Z), natural mortality (M) and fishing mortality (F) were estimated as 4.36, 2.64 and 1.72 year-1 respectively. The assessment revealed that 95.8% of the exploited catch is above the optimum length (Lopt), of 30 mm. The exploitation rate (E) and exploitation ratio (U) were 0.394 and 0.389, respectively and the maximum sustainable yield (MSY) of P. malabarica was 104.8 t which shows the present catch was 21% below the MSY. The above results indicate scope for expansion of the fishery of the species in Karapad Bay.

Keywords: Age, Biology, Population, Stock assessment, Short neck clam