Do krill fisheries compete with macaroni penguins? Spatial overlap in prey consumption and krill catches during winter

Aim  To infer the potential for competition between an important Antarctic predator, the macaroni penguin, and the krill fishery by examining the spatial overlap in prey consumption and catches.

Location  South Georgia, Scotia Sea and adjacent waters.

Methods  The study focused on the winter period as this is the only time of year when spatio-temporal overlaps between macaroni penguin foraging and the krill fishery can occur. We tracked adult macaroni penguins from a colony in South Georgia using global location sensors to determine winter distribution, and bioenergetics models to calculate biomass of food consumed during the winter period. We combined these to produce a surface of the tonnes of krill consumed which could be compared directly with the spatial distribution of the tonnes of krill caught by the fishery.

Results  Adult macaroni penguins from South Georgia consumed 126,472 tonnes of krill during the winter which is similar to the 98,431 tonnes caught by fisheries over the same period. However macaroni penguins had a very wide pelagic distribution across the Scotia Sea whereas the fishery was restricted to three small areas on shelf edges, such that their spatial overlap was negligible. The proportion of the estimated krill stock taken by macaroni penguins and the krill fishery was small both at the scale of the Scotia Sea and the local areas within which the fisheries operate.

Main conclusions  Competition between macaroni penguins and the krill fishery is low under current management and far less than that among the various other species of krill predators that occur in the Scotia Sea. Our method will allow quantification of changes in competition between macaroni penguins and krill fisheries should the latter expand in the future, and provides a framework for assessing predator-fishery competition in other systems.