Reproductive biology and population characteristics of Sardinella gibbosa and Sardinella fimbriata from north west Bay of Bengal

Abstract

Reproductive biology and population characteristics of Sardinella gibbosa and Sardinella fimbriata landed by gill netters from north west Bay of Bengal was studied during 2005 – 2010. Average annual catch was 21080 t, in which the contribution of S. gibbosa was 12790 t and the contribution of S. fimbriata was 8290 t. SST, rainfall and chlorophyll a were found to affect the annual catch of lesser sardines. Length weight relation showed differential growth between adults and indeterminates for both the species. Overall sex ratio varied between 1:1.28 to 1:1.33 for S. gibbosa and between 1:1.02 to 1:1.025 for S. fimbriata with length at first maturity of 13.03 cm for S. gibbosa and 13.27 cm for S. fimbriata. Peak spawning season was February – April for S. gibbosa and May - July for S. fimbriata. Total fecundity ranged between 12786 ova to 68377 ova for S. gibbosa and between 11066 ova to 60981 ova for S. fimbriata. Mature ovaries in lesser sardines contained both immature and mature ova. Von Bertalanffy growth equation was Lt = 20.7 [1 – e - 0.96 (t + 0.018)] for S. gibbosa and Lt = 20.7 [1 – e - 0.85 (t + 0.023)] for S. fimbriata. Natural mortality, fishing mortality, total mortality and exploitation rate were 1.90, 3.56, 5.46 and 0.65 for S. gibbosa and 1.75, 2.57, 4.32 and 0.59 for S. fimbriata, respectively. A higher value of E than E0.5 for both Sardinella gibbosa and Sardinella fimbriata and a lower value of Maximum Sustainable Yield than annual average catch indicate intensive fishing of lesser sardines along north west Bay of Bengal.