Climate- and density-dependent regulation of fish growth throughout ontogeny: North Sea sprat as a case study

Growth is a fundamental physiological process influencing the state and dynamics of fish stocks, yet the physical and biological conditions affecting individual weight and growth throughout ontogeny are poorly known and often unaccounted for in fisheries management. This is rather surprising given that changes in growth have strong direct effects on the total biomass and potential yield derived from any given stock. In this study, we investigate the underlying factors affecting fish growth throughout the life span of cohorts using statistical modelling and long-term observational data on sprat (Sprattus sprattus), a commercially and ecologically important small-pelagic fish species across European seas. Our results demonstrate a negative relationship between total abundance and weight, as well as a positive and dome-shaped relationship between temperature and zooplankton abundance (i.e. food availability), respectively. Furthermore, we demonstrate how such improved knowledge and understanding of the underlying factors affecting weight and growth could be accounted for in future assessment models, by including these considerations into short-term forecast simulations. This, in turn, would provide a stronger scientific basis for management advice and ensure the sustainability and profitability of fisheries, particularly on small and commercially valuable pelagic species with pronounced spatio-temporal variability in weight and growth.