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.

Atresia of ovarian follicles in fishes, and implications and uses in aquaculture and fisheries

“…However, it is widely reported that the Atlantic cod may not spawn annually once reaching maturation (Rideout et al., 2000 and references therein cited). Electronic tagging experiments and fishery data have shown that not all the adult individuals of the highly migratory species Atlantic bluefin tuna visit any of the known spawning grounds during the spawning season, thus leading to the disputed hypothesis that only a fraction of the adult population contributes to recruitment (Bello et al., 2021 ; Corriero et al., 2020 ; Medina, 2020 ), a reproductive strategy that could involve follicular atresia as mechanism underlying spawning omission.…”

An autofluorescence‐based survey of late follicular atresia in ovaries of a teleost fish (Thunnus thynnus)

“…The occurrence of early atretic stages of yolked follicles (α and β atresia) is often used in fish maturity classifications and characterization of temporal reproductive patterns (e.g., Lowerre-Barbieri et al, 2011;Schaefer, 1998Schaefer, , 2001. Degenerated yolked follicles are helpful to distinguish reproductively inactive, but mature, individuals from young fish that have not yet attained maturity, which is a crucial issue in fisheries science (Arrizabalaga et al, 2019;Medina, 2020).…”

Multiple-Phase Biometric Relationships and Sexual Maturity in the Atlantic Bluefin Tuna, Thunnus thynnus (Osteichthyes: Scombridae)

“…The adoption of appropriate biometric models holds notable importance in the case of ABFT, as its age-at-reproduction is presently a matter of debate [ 19 , 20 ]. The International Commission for the Conservation of Atlantic Tunas (ICCAT) manages ABFT on the assumption that the two recognized stocks, i.e., the Western and the Eastern Atlantic stocks, have different sexual maturation schedules and strict spawning fidelity to the respective reproductive areas (Gulf of Mexico and the Mediterranean Sea) [ 21 ].…”

“…The International Commission for the Conservation of Atlantic Tunas (ICCAT) manages ABFT on the assumption that the two recognized stocks, i.e., the Western and the Eastern Atlantic stocks, have different sexual maturation schedules and strict spawning fidelity to the respective reproductive areas (Gulf of Mexico and the Mediterranean Sea) [ 21 ]. This disputed assumption is backed by controversial determinations of main life traits, such as age- and size-at-sexual maturity [ 19 , 20 ]. In this respect, any piece of evidence able to shed light on the age- and size-at-first reproduction is highly welcome.…”