A study of Mediterranean bluefin tuna (Thunnus thynnus L.) with reference to stock identification and management strategies
The management of bluefin tuna (Thunnus thynnus) in the north Atlantic has been based on the assumption that there are two separate stocks (an eastern Atlantic stock, including the Mediterranean Sea and a western Atlantic stock). This hypothesis has never been scientifically confirmed. This study provides evidence of unique stock characteristics of the bluefin tuna population targeted specifically in the Mediterranean and aims at showing that it is a single stock suitable for its own management regime. This has been done through the study of the biological parameters of bluefin tunas sampled in the Mediterranean, including biometric relationships, age determination, size at first maturity and reproductive studies. The identity of the Mediterranean stock has also been examined through tagging activities, extraction and chemical analysis of the otoliths and through genetic studies. Old and new exploitation techniques within the Mediterranean have been analysed in order to identify trends in landings, existence of illegal, unreported and unregulated catches and to conclude whether or not the bluefin tuna population in the Mediterranean is being overexploited. Results obtained all lead to the conclusion that the Mediterranean stock is an independent stock confined to the Mediterranean with minimal exchange through the Strait of Gibraltar. This study provides a strong argument for the management of the bluefin tuna population in the Mediterranean as a unique stock biologically independent of the Atlantic stock.