European anchovy (Engraulis encrasicolus) populations of the North Sea increased dramatically since the 1990s, while usually being present only further South like the Bay of Biscay or Mediterranean Sea. This poses the questions of what ecosystem effects this will engender and why this change occurred when it did. Temperature and food availability changes are likely candidates to address the latter, and for the former, impacts on habitat and food availability for other planktivores such as the highly commercial herring (Clupea harengus) are the most pressing. Herring has shown low recruitment since 2000 and the role of changed abundance of other prey or potential competitor species is not well understood. We combine empirical work and spatio-temporal statistical modeling to address these questions. The composition and diversity in diets of anchovy, and two co-occurring clupeids: sprat (Sprattus sprattus) and herring were compared based on stomach analyses. Furthermore, the distribution in space and time of anchovy is compared to that of its likely prey items using generalized additive modeling on data from the Continuous Plankton Recorder (curtesy of SAHFOS) and the International Bottom Trawl Survey (curtesy of ICES).
Results/Conclusions
Anchovy diet was more diverse at both the population and at the individual level than the diets of sprat and herring respectively, indicating that anchovy may be able to feed on a more variable plankton environment than the other species. The distribution of anchovy in the North Sea was best explained by temperature and spatial effect, while biomass of zooplankton, and abundance of major prey items did not explain anchovy distribution. We thus conclude that the reason for anchovy increase in the North Sea is not related to food availability, and its impact on potential competitors is unlikely to be related to food. Habitat interactions may play a role that needs to be further elucidated using the sparse data available on this new and uncommercialized species in the North Sea.