Kittiwake breeding success in the southern North Sea correlates with prior sandeel fishing mortality

In the North Sea, sandeels provide a vital food source for breeding seabirds, but are also the target of an industrial fishery. GPS tracking suggests that the most productive fishing grounds overlap with foraging areas of black-legged kittiwakes from eastern England, raising the prospect that the fishery could affect the birds. Rising sea temperatures also threaten sandeels, so kittiwake food supplies could be affected by local and larger-scale processes. Drivers of kittiwake breeding success at Flamborough Head and Bempton Cliffs Special Protection Area, the UK's largest colony, and one of the closest to the sandeel fishing grounds, were examined. Relationships between sandeel stocks, sea surface temperature and kittiwake breeding success were analysed with generalized linear mixed models and generalized linear models, with model performance assessed using the Akaike Information Criterion and R2. Higher kittiwake breeding success was associated with higher sandeel spawning stock biomass (SSB; biomass of sexually mature fish) the preceding winter (R2 = 21.5%) and lower sandeel fishing mortality two years previously (R2 = 22.3%). After temporal trends were removed, only the fishing mortality effect remained. Models with multiple predictors supported the importance of fishing mortality. Higher sandeel SSB was associated with lower temperatures (R2 = 15.2–38.6%) and lower sandeel fishing mortality (R2 = 24.2–26.1%). Hence, lower temperatures and fishing mortality were positively associated with sandeel biomass, and higher sandeel biomass and lower fishing mortality were positively associated with kittiwake productivity. In light of worsening environmental conditions and declining sandeel and kittiwake populations, careful consideration should be given to the requirements of sandeel-dependent predators when making fishery management decisions.