Population dynamics of two squid species, <em>Uroteuthis duvaucelii</em> (D'Orbigny, 1835) and <em>U. singhalensis</em> (Ortmann, 1891) (Family: Loliginidae) in the Trincomalee bay, Sri Lanka

Abstract

In the Trincomalee bay of Sri Lanka, two species of squids, Uroteuthis duvaucelii and U. singhalensis, support profitable small-scale fisheries. The present study is an attempt to assess the fisheries of these two squid species using length-based stock assessment methodologies. Length frequency data collected from the landings of two species, collected during the fishing season from May to October 2003 were analyzed using FiSAT II software package. The asymptotic length (mantle length) and growth constant of U. duvaucelii were 31.8 cm and 0.90 yr-1 respectively and of U. singhalensis were 31.2 cm and 0.72 yr-1 respectively. Using the mortality coefficient estimates based on these growth parameters, exploitation rates (E) of U. duvaucelii and U. singhalensis during the study period were found to be 0.55 and 0.44 respectively. Optimal fishing strategies determined by relative yield-per-recruit (Y’/R) analyses of two squad species indicated that the sizes of first capture (Lc) and E were at sub-optimal levels. As both squid species are exploited by the same fishing gear, optimal E values predicted by Y’/R analyses cannot be achieved. This analysis indicates that levels of exploitation during the study period having Lc of 15.8 cm for U. duvaucelii at E = 0.55 and 14.3 cm at E = 0.44 for U. singhalensis be maintained. It is therefore concluded that fishing effort and the sizes of the first capture of the two squid species in the Trincomalee bay do not require adjustments through fishery regulations for the sustainability of their fisheries.