Abstract
Achieving sustainable management of marine resources and implementing biologically realistic assessment depend on accurate identification of stock structure. Most harvested marine species are currently assessed under the common and long-standing assumption of “stock unit” within designated spatiotemporally invariant polygons known as assessment units, despite evidence of passive and/or active dispersal across multiple scales. Our objective here is to investigate the connectivity and spatial structure of red mullet (Mullus barbatus) metapopulation system in the Northwestern Mediterranean Sea and compare the delineation of assessment units with biological units. To achieve this, we integrate simulated larval dispersal modelling with tissue stable isotope analysis, encompassing the entire life cycle. We observe misalignment between the present “closed” assessment units and the identified biologically informed units. The identified metapopulation system comprises northern and southern subpopulations with dissimilar demographic roles. This principally stems from the Northern Current mediated larval transport from high-density persistent spawning grounds and, secondarily, likely from the regional differences in the isotopic baseline associated with different productivity regimes. Such an interdisciplinary approach is of elevated importance for species with stark differences across their life history, such as red mullet. Moreover, larval connectivity diagnostics successfully capture the interannual variability of recruitment dynamics of this complex stock, evidencing the capacity of biophysical models to inform fisheries assessment and management. This study highlights the importance of implementing spatial stock assessment frameworks that rely on critical, yet still largely disregarded, ecological information.
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Acknowledgements
This study was realized within COCOCHA project (PID2019-110282RA-I00, Spanish Ministry of Science and Innovation). GK acknowledges funding from the Grant for PhD candidates (FPI) PRE2020-094321 funded by MCIN/AEI/10.13039/501100011033 and co-funded by the European Social Fund (ESF+ investing in people’s future). ES-G acknowledges support from grant PID2021-123352OB-C32 funded by MICIU/AEI/10.13039/501100011033 and FEDER, ‘Una manera de hacer Europa’. We thank all the dedicated people of the Instituto Español de Oceanografía (IEO-CSIC, Spain) and IFREMER (IFREMER, France), who have worked on the research vessels and MEDITS surveys. MEDITS surveys are funded by IEO, IFREMER and the European Union (EU) through the European Maritime and Fisheries Fund (EMFF) within the National Program of collection, management and use of data in the fisheries sector and support for scientific advice regarding the Common Fisheries Policy. GK was partially funded by the Erasmus+ Programme of the European Union and from an STSM grant from COST Action SEA-UNICORN CA19107, supported by COST (European Cooperation in Science and Technology). VR acknowledges financial support from the INSU-CNRS MISTRALS program through its regional networking initiative ENVI-Med that funded the HYDROGENCONNECT project, from the European Space Agency (ESA Contract No. 4000141547/23/I-DT) through the 4DMEDSEA project granted to CNR (Italy) that subcontracted AMU (France). The project leading to this publication has received funding from European FEDER Fund under project 1166-39417. VR, MH and LLL acknowledge funding from EuroMarine through the Foresight Workshop TUTTI (From species connectivity To fUncTional connecTIvity). Correspondence regarding this work should be addressed to Georgios Kerametsidis and Manuel Hidalgo, who are joint corresponding authors.
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Kerametsidis, G., Hidalgo, M., Mourre, B. et al. Evidence of within- and between-stock connectivity in Mediterranean fisheries challenges the stock unit paradigm.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-47826-7
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DOI: https://doi.org/10.1038/s41598-026-47826-7
Source: Ecology - nature.com
