Reproduction of Atlantic bluefin tuna

Abstract

The reproductive success of fish populations depends on their reproductive potential and offspring survival to maturity. The reproductive potential affects recruitment and hence populations’ resilience and productivity. Extensive research carried out throughout the current century has improved our understanding of the reproductive biology of the Atlantic bluefin tuna (ABFT), Thunnus thynnus. Yet, crucial questions still remain unresolved. This paper examines key factors that drive ABFT reproductive performance (maturity, spawning frequency, fecundity, sex-ratio, spawning habitat). Some reproductive variables (spawning-at-age, spawning omission, egg and offspring viability, parental effect) remain poorly investigated due to the enormous challenge of implementing the required research across the distribution range and over time. These fundamental traits of the reproductive life history, however, provide valuable information to fish stock assessment models, and hence require further attention. There is a major debate as to the extent of similarity in reproductive traits between eastern and western ABFT stocks. Both stocks have been considered to display differing maturity schedules, which would result in different spawning rates and reproductive outputs. Yet, similarities have been found in major reproductive aspects suggesting that discrepancies between stocks may not be as broad as often assumed. Though substantial, the information acquired on ABFT reproduction over the years is still incomplete for adequately advising fisheries management. The present report provides a synthesis of the existing information on the reproductive biology of ABFT. It also identifies major research needs and analyses future research actions towards bridging current gaps in ABFT reproduction science.