Influence of temperature and food availability on juvenile European anchovy Engraulis encrasicolus at its northern boundary

The European anchovy Engraulis encrasicolus population of the North Sea has increased and spread in recent decades, probably in response to the relaxation of limiting factors in its life history. We use models and empirical data to explore the effects of temperature and food availability during the first growing season on the adult anchovy population across the North Sea. First, we compare simulated growth during summer and autumn, from a dynamic energy budget model, with trends in the time series of anchovy survey catch per unit effort. The proportion of the area of the North Sea in which anchovy can grow to 10 cm (the potential growth habitat) correlates with the abundance of anchovy caught in surveys the following year. Second, spatio-temporal statistical modeling is used to show that anchovy abundance in surveys is related to environmental variables (temperature and food availability). Temperature explains the distribution and abundance of anchovy in the North Sea better than food availability or a combination of both environmental factors. We conclude that variations in growth during the first months of life can impact anchovy life cycle closure. Specifically for the North Sea anchovy, changes in temperature are more important than changes in food availability in allowing the fish to grow to overwintering size, under probably non-food-limited conditions.