Length at first maturity and length at first capture for bullet tuna (Auxis rochei Risso, 1810) in the southern waters of Bali

Abstract

Bullet tuna (Auxis rochei Risso, 1810) is one of the neritic tuna species which has the second largest number of catches after small pelagic fish. The high potential for neritic tuna has a risk of continuous fishing pressure. This study presents mainly two biological indicators, the length at first capture (Lc=L50%) and the length at first maturity (Lm50) of bullet tuna, based on the biological data collected from the southern waters of Bali from June to November 2021. Parameters and characteristics of biological aspects are expected to be useful in policies in determining the optimum catch size, restrictions on fishing effort and determining the optimum of mesh size to be used in commercial fishing. Biological sampling was conducted at Fish Landing Base Kedonganan Bali from the catches of the neritic gillnet. A total of 151 female fish and 95 male fish were studied. Fresh gonad samples were fixed and analyzed histologically by a paraffin method and Harris-Haematoxylin and Eosin staining. The results showed that the length at first capture (Lc=L50% = 20,1 cm) was significantly lower than the length at first maturity (Lm50 = 22,76 cm); this was indicating that the young fish (the immature and never spawn) were dominant in the catch and would lead to an overfishing status. It is recommended that the fishing efforts and gear selectivity of bullet tuna with neritic gillnets must better manage for the sustainability of the fish resources.