Mismatches between genetic and assessment units in commercial fish species: A systematic review in the North-East Atlantic.

While sustainable fisheries depend upon spatial and temporal identification at below the species level (i.e., stock units), the choice and identification of appropriate units remain challenging. Advances in DNA sequencing and improved computational power have generated extensive genetic and genomic data on the spatio-temporal dynamics and resolution of marine fish populations. Here, we clarify terminology employed to designate fishery units and highlight the benefits of alignment between assessment units and biological processes. Our systematic review synthesises four decades of population genetic and genomic data in major North-East Atlantic commercial fishes, appraising mismatches between genetic and assessment units. We confirm the progressive increase of genetic data, also indicating an increased detection of genetic population structure. Patterns of small-scale temporal and spatial differentiation yield demonstrable tools for elucidating the integrity and dynamics of assessment units, including in mixed-stock fisheries. Atlantic cod (Gadus morhua) and herring (Clupea harengus) remain extensively researched (46% of the reviewed studies). We found that genetics is informing realignment of stock boundaries, with increased incidence of alignment between genetic and assessment units, though mismatches persist for many stocks. Moreover, several species and fisheries lack genetic data. With reduced costs of molecular analysis and implementation of real-time applications, we anticipate increased re-evaluation of stock boundaries and monitoring of complex population structure, providing baseline genetic tools for management of mixed-stock fisheries and inclusion of genomic data in stock assessment models. Generating reference genetic databases of populations will also facilitate studies on distributional range shifts in marine fishes, supported by increasingly precise predictive forecasting in a changing world.