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Seasonality of diet overlap among small pelagic fish in the waters southwest of the UK

Roweena Patel*, Shovonlal Roy, Elisa Capuzzo, Jeroen van der Kooij

*Corresponding author:

ABSTRACT: Small pelagic fish (SPF) play an important ecological role by facilitating energy transfer in marine ecosystems, from lower to higher trophic levels. The Celtic Seas ecoregion is home to several economically important SPF that spend some or all their life in these waters. In recent decades, major changes in the relative abundances of the six main SPF in the region (anchovy, herring, horse mackerel, mackerel, sardine, and sprat) have been observed. Changes in the region may impact SPF, previous studies in neighbouring seas have highlighted possible diet overlap of these species, therefore, it is important to understand the changes in diet overlap and trophic relationships, particularly across different seasons. Consequently, we investigated seasonal diet composition of these six SPF in the Celtic Seas ecoregion, identified diet overlap and determined species selectivity towards different sized prey. Combining historical and recent observations on fish-stomach content, diet-overlap indices were computed to quantify potential seasonal intra- and inter-specific overlap. Diet overlaps among species changed between seasons, in particular, sprat and anchovy changed significantly between spring and autumn, and mackerel between spring, summer, and winter. SPF species primarily consumed calanoid copepods with herring and horse mackerel having more selective diets compared to mackerel, anchovy, and sardine. All species fed at similar trophic levels between seasons. To our knowledge, this study, for the first time, showed seasonal variability in diet overlap among the six SPF in the Celtic Seas ecoregion. These results can improve the understanding of feeding dynamics for SPF in ecosystem model outputs.