Review of Sexual Maturity in Atlantic Bluefin Tuna, Thunnus thynnus (Linnaeus, 1758)

The age of sexual maturity of the Atlantic bluefin tuna (Thunnus thynnus; ABFT) is a reference point for stock assessment and management. The International Commission for the Conservation of Atlantic Tunas (ICCAT) recognizes a western and an eastern Atlantic ABFT stock, based on the assumptions of separate, exclusive spawning grounds, i.e., the northern Gulf of Mexico and the Mediterranean Sea, with different ages of sexual maturity, 8-12 years vs 3-5 years, respectively. Multiple line of evidences indicate that spawning is not restricted to the Gulf of Mexico and the Mediterranean Sea, and reconsideration of historical documents, as well as results from recent studies, indicate that sexual maturation schedules of the two proposed stocks are similar (3-5 years). The present review of classical and recent literature suggests that ABFT have more complex reproductive behavior than previously considered: on eastern spawning grounds 50% of ABFT females reproduce at 3 years of age and 100% are sexually mature at 5 years of age. In the western management area, younger adults (age >= 5 years) and some larger adults apparently spawn in the northwest Atlantic Ocean across the Slope and Caribbean Seas, whereas the Gulf of Mexico spawners are mostly large adults (age >= 8 years).