Implications for Atlantic Bluefin tuna conservation and
management
Conservation of ABFT is challenged by past and future fishing pressure
(Fromentin et al. 2014a,
Secor et al. 2015), which has sharply
increased over the last five years following the rebuilding of the
Mediterranean ABFT population (ICCAT
2023), and by changes in environmental conditions (often interacting
with fishing pressure), which have been shown to alter population size
and productivity, migratory behavior and spatial distribution
(Ravier and Fromentin 2004). From a
conservation perspective, hybridization between genetically
differentiated lineages, in this case between GOM-like and MED-like
individuals, could increase each population’s genetic diversity, leading
to the incorporation of potentially adaptive genomic variation and
reducing vulnerability to environmental changes
(Brauer et al. 2023). However, strong
unidirectional gene flow could provoke genetic swamping of the western
Atlantic spawning areas jeopardizing ABFT genetic diversity
(Roberts et al. 2010). In this sense,
large effective population sizes, which could increase following a
rebuilding of abundance at the different spawning areas
(Hoey et al. 2022) would counteract the
homogenizing effect of genetic drift. In the absence of accurate
estimations of ABFT effective populations sizes
(Puncher et al. 2018), further genetic
monitoring of temporal samples could help to understand potential
ongoing trends in genetic diversity conservation
(Hoban et al. 2014,
Oosting et al. 2019).
From a fisheries management perspective, the confirmation of ongoing
admixture in the Slope Sea challenges the paradigm of two isolated ABFT
stocks. However, large knowledge gaps related to the dynamics of Slope
Sea individuals, the magnitude of the Slope Sea spawning in terms of
recruitment, and its demographic connectivity with other components
hinders explicit modelling of it as a distinct stock. Nonetheless, the
recently adopted management procedure
(ICCAT 2023) does explicitly consider
spawning in the Slope Sea. Our study highlights the need for further
monitoring combining multidisciplinary data such as larval sampling,
tagging, otolith microchemistry signature and genetic origin to
understand the Slope Sea population dynamics and the relevance of this
spawning area in demographic and evolutionary terms.