At-Sea Distribution and Prey Selection of Antarctic Petrels and Commercial Krill Fisheries

Abstract

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 krill-dependent 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.

Antarctic petrels ‘on the ice rocks’: wintering strategy of an Antarctic seabird

“…Among those, the Antarctic petrel (Thalassoica antarctica) is a wide-ranging species and yearround resident of Antarctic waters [14]. Antarctic petrels generally forage in close association with sea ice, cold water-masses and icebergs [9,[14][15][16][17][18], where they capture primarily pelagic fish and crustaceans [19,20]. As such, any change in the icescape may have immediate consequences for petrel demography [21] and probably for their survival rate, as has been shown in other seabird species [22].…”

Density dependence forces divergent population growth rates and alters occupancy patterns of a central place foraging Antarctic seabird

“…For example, Adélie penguins are thought to mediate intraspecific competition by geographic structuring of breeding colonies (Ainley, Nur, & Woehler, 1995) and by spatial partitioning of foraging in neighboring colonies (Ainley et al, 2004). Interspecific competition between Adélie penguins and flying seabird species is also likely to be mediated by their strong horizontal and vertical spatial partitioning in foraging (Clarke et al, 2006;Dehnhard et al, 2019;Descamps et al, 2016;Whitehead, 1989), even though they have broadly similar diets of krill and fish (Green & Johnstone, 1988;Lorensten, Klages, & Røv, 1998;Nicol, 1993;Tierney, Emmerson, & Hindell, 2009). A third explanation, given the notorious difficulty of quantifying competition and the abundance of mid-trophic organisms in marine ecosystems (Oro, 2014), is that our indices did not accurately reflect the true availability of food.…”

Peer Review #1 of "Differences in tail feather growth rate in storm-petrels breeding in the Northern and Southern hemisphere: a ptilochronological approach (v0.2)"

“…The relatively short period of high food abundance and possible competition over it [e.g. from penguins, whales and krill fisheries (Barlow et al, 2002;Descamps et al, 2016;Ratcliffe et al, 2015)] could inhibit the Southern storm-petrels from overlapping moult and breeding as there is no longer enough food available at the end of the breeding season.…”