Black-Legged Kittiwake Breeding Performance as an Indicator of Effective Forage Fish Availability

If seabird breeding metrics correlate with accessible food resources, breeding performance can serve as a contextual signal reflecting marine food supply status. This review synthesizes evidence linking black-legged kittiwake (Rissa tridactyla) breeding performance to effective forage fish availability, focusing on lesser sandeels within the North Sea. Synthesized findings from food supplementation trials, prey surveys, animal tracking datasets, long-term monitoring records, and fishery closure analyses demonstrate that prey abundance, age structure, and phenological synchrony between prey occurrence and bird breeding jointly shape reproductive outcomes. Fishing impacts depend on spatial overlap among fishing grounds, prey distributions, and colony foraging ranges. Predation and colony-local disturbances may also depress breeding success, creating ambiguity in causal inference. No universal prey density threshold can be derived to directly convert breeding performance into total fish biomass estimates. Standardized monitoring that separates breeding stages and integrates complementary datasets on prey, seabird diets, fisheries and predation is required to deploy this indicator reliably at local and regional scales.