Evidence of predation events by marine mammals at offshore wind farms

Anthropogenic structures in the marine environment alter the availability and distribution of food for marine animals with potential consequences for individual fitness, population and community dynamics. Knowledge of how existing wind farm sites influence the behaviour or foraging activities of marine mammals is valuable if predictions on the effect future large-scale renewable energy development will have on local or regional populations are to be made. During acoustic tracking of demersal gadoid fish at two offshore wind farms in Scotland, six Atlantic cod were predated by a marine mammal close to or in the vicinity of turbine foundations. The distinct change in the temperature, depth and movement pattern of the acoustic tags allowed estimations of the time and location of predation (and likely predator) and provided details of post consumption behaviour. The detection of tags (predator) at multiple turbines within a relatively short period, post consumption, suggests the targeted use of turbine foundations as foraging sites where prey fish are known to aggregate. Moreover, the bias in predation of cod over haddock, and evidence for the cod being of higher energetic quality, provide rare evidence for prey selection by a marine mammal predator(s). These data provide further evidence for how wind farms and other introduced structures influence the behaviour of marine mammals with potential consequences for individuals and populations through changes in the distribution of prey. The ultimate consequences are to be determined but need consideration with the continued development of offshore wind farm sites.