Modelling and mapping trophic overlap between fisheries and the world’s seabirds

Seabird food consumption may reveal the potential for competition between seabirds and fisheries. I ndeed, coexistence of foraging seabirds and operating fisheries inevitably results in interactions, one of which is competition for the same resources. I used GIS-based modelling at a scale of 30-min spatial cells to: (a) map the foraging distribution of seabirds; (b) predict their annual food consumption rates in a spatially-explicit manner; and (c) estimate a spatially-explicit seabird - fisheries overlap index. Information on the population size, diet composition and foraging attributes of 351 species of seabirds was compiled into a Microsoft Access database. Trophic levels, expressing the position of seabirds in the marine ecosystem, were estimated for each species using diet composition data. Global annual food consumption by seabirds was estimated to be 96.4 million tonnes (95% CI: 78.0 to 114.7 million tonnes), compared to a total catch of nearly 120 million tonnes by all fisheries. Krill and cephalopods comprised over 58% of the overall food consumed and fishes most of the remainder. The families Procellariidae (albatrosses, petrels, shearwaters, etc.) and Spheniscidae (penguins) were responsible for more than 54% of the overall food consumption. Mapping the foraging distribution of seabirds revealed that, areas near New Zealand, the eastern coast of Australia, and the sub-Antarctic islands have high seabird species richness. Hawaii and the Caribbean were the only areas north of the equator with high species richness. Temperate and polar regions supported high densities of seabirds, and most food extracted by seabirds originated there. In addition, maps of the annual food consumption rates revealed that most of the food consumed by seabirds was extracted from offshore waters rather than nearshore ones, and from areas where overlap between seabirds and fisheries was low. My trophic overlap maps identified 'hotspots' of highest potential for conflict between fisheries and seabirds. Thus, this study may provide useful insight when developing management approaches to manage marine conservation areas.