Age and growth determination and stock identification using statolith microstructure of Indian squid, Loligo duvauceli

Abstract

Age and growth and stock identification of Indian squid, Loligo duvauceli were examined by statolith microstructure and morphological measurements. The Indian squid were sampled from the Gulf of Thailand and the Andaman Sea by otter board trawlers. The age in days after hatching for the Indian squid from the Gulf of Thailand ranged from 61 to 153 days and the Andaman Sea ranged from 76 to 270 days. The Growth Index (GI) was not significantly different between sexes for both seas. The GI of males and females were 0.959 and 1.044 mm/day for the Gulf of Thailand and 0.730 and 0.706 mm/day for the Andaman Sea. A logarithmic function was selected to describe the population growth pattern for both seas. Sexual dimorphism appeared in both two populations. The maturity pattern was more distinctly separated by DML than age for both sexes. The DML50% for males and females was 78.90 and 94.05 mm for the Gulf of Thailand and 100.69 and 91.52 mm for the Andaman Sea. These lengths are smaller than previous studies, and may show evidence of fisheries induced evolution to earlier maturation at smaller sizes. Both morphological and statolith variables were apparent for L. duvauceli stocks identification using Discriminant Analysis.