Abstract
<title>Abstract</title> <p>Fish form a critical energetic link between trophic levels in marine ecosystems. Their energy content reflects habitat quality and individual fitness, and determines their profitability for marine top predators. In a rapidly changing marine environment, historical energy values and length-weight relationships require updating to remain relevant for ecological studies. This study addresses the paucity of data on the energy content of prey species for marine top predators in the North Sea using bomb calorimetry to derive contemporary energy density (kJ g-1) values for 34 fish and two cephalopod species. Length-weight and length-total energy (kJ) relationships were established for 21 species across 10 families. Seasonal differences were evident in Raitt’s sandeel (Ammodytes marinus), which showed greater total energy in winter compared to summer, highlighting the importance of temporal context. These results provide insights into intra- and inter-specific variation in prey quality and the scaling of total energy content with fish size. It represents a key resource for studies on predator energetics, predator-prey dynamics, population modelling, and assessments of anthropogenic impacts on marine ecosystems. Collectively, these findings can inform long-term evaluations of fish quality and management strategies and contribute to our understanding of energy flow in coastal marine food webs.</p>