Aspects of fisheries biology of bluefin tuna, Thunnus thynnus (L.), in the Maltese Islands

Abstract

This study concerns some aspects of the fisheries biology of one of the most highly prized species in the world i.e. the bluefin tuna, Thunnus thynnus (L). Firstly, a synoptic description of the bluefin tuna fishery, which includes fishery statistics, and a description of the fisheries and fishing methods is given. This is followed by a study on the more relevant biological parameters of tunas. Tuna catches are strongly related to environmental factors, mainly temperature of surrounding water, depth and wind conditions. Gonadosomatic index and histological analysis indicated that the females caught were in their spawning phase. 45% of dissected stomachs were found empty. Squid and mackerel make up the main prey of bluefin tuna. During the months of May and June, measurements of length and weight of the 1295 bluefin tuna landed at the fish market were taken. From these an age length graph was produced for the Maltese Islands. The largest number of tuna weighed between 150 and 199 kg, had a fork length between 150 and 199 cm and was between 5 and 10 years old. Bycatch included swordfish, Mediterranean marlin, oilfish, blue shark, dolphin fish and albacore.