Population structure of Greenland halibut across the North Atlantic inferred from large-scale monitoring and spatial modelling

Abstract The Greenland halibut (Reinhardtius hippoglossoides) is an ecologically and economically important marine fish species in the Northern Hemisphere. In the North Atlantic, the current spatial management units comprise four large offshore stocks and eight additional inshore stocks. However, the underlying biological basis for stock separation is uncertain. This may risk misrepresenting key population characteristics and reference points for sustainable management. To identify population structuring and boundaries for Greenland halibut, we here apply a spatial statistical approach using an extensive collection of scientific bottom trawl-surveys. Our analysis demonstrates two overall clusters separating the Northwest and Northeast Atlantic. Our findings are broadly consistent with recent studies on population structuring based on available tagging data and population genetics. However, it is still challenging to establish whether the results of clustering accurately reflect the true population boundaries, especially at a finer spatial scale. Therefore, we call for a broader synthesis of knowledge on population structuring of Greenland halibut utilizing all available sources of information to facilitate the designation of ecologically relevant management units and boundaries.