At-sea distribution and prey selection of Antarctic petrels and commercial krill fisheries
Résumé
Commercial fisheries may impact marine ecosystems and affect populations of predators
like seabirds. In the Southern Ocean, there is an extensive fishery for Antarctic krill Euphausia
superba that is projected to increase further. Comparing distribution and prey selection
of fishing operations versus predators is needed to predict fishery-related impacts on krilldependent
predators. In this context, it is important to consider not only predators breeding
near the fishing grounds but also the ones breeding far away and that disperse during the
non-breeding season where they may interact with fisheries. In this study, we first quantified
the overlap between the distribution of the Antarctic krill fisheries and the distribution of a
krill dependent seabird, the Antarctic petrel Thalassoica antarctica, during both the breeding
and non-breeding season. We tracked birds from the world biggest Antarctic petrel colony
(Svarthamaren, Dronning Maud Land), located >1000 km from the main fishing areas, during
three consecutive seasons. The overall spatial overlap between krill fisheries and Antarctic
petrels was limited but varied greatly among and within years, and was high in some
periods during the non-breeding season. In a second step, we described the length frequency
distribution of Antarctic krill consumed by Antarctic petrels, and compared this
with results from fisheries, as well as from diet studies in other krill predators. Krill taken by
Antarctic petrels did not differ in size from that taken by trawls or from krill taken by most Antarctic
krill predators. Selectivity for specific Antarctic krill stages seems generally low in Antarctic
predators. Overall, our results show that competition between Antarctic petrels and
krill fisheries is currently likely negligible. However, if krill fisheries are to increase in the
future, competition with the Antarctic petrel may occur, even with birds breeding thousands
of kilometers away.