Using seabird and whale distribution models to estimate spatial consumption of krill to inform fishery management

Ecosystem dynamics at the north-west Antarctic Peninsula are driven by
interactions between physical and biological processes. For example,
baleen whale populations are recovering from commercial harvesting against
the backdrop of rapid climate change, including reduced sea-ice extent and
changing ecosystem composition. Concurrently, the commercial harvesting of
Antarctic krill is increasing, with the potential to increase the
likelihood for competition with and between krill predators and the
fishery. However, understanding the ecology, abundance, and spatial
distribution of krill predators is often limited, outdated, or at spatial
scales that do not match those desired for effective fisheries management.
We update current knowledge of predator dependence on krill by integrating
telemetry-based data, at-sea observational surveys, estimates of predator
abundance, and physiological data to estimate the spatial distribution of
krill consumption during the austral summer by three species of Pygoscelis
penguin, 11 species of flying seabirds, one species of pinniped and two
species of baleen whale. Our models show that the majority of important
areas for krill-predator foraging are close to penguin breeding colonies
in nearshore areas where humpback whales also regularly feed, and along
the shelf-break, though we caution that not all known krill predators are
included in these analyses. We show that krill consumption is highly
variable across the region, and often concentrated at fine spatial scales,
emphasising the need for management of the local krill fishery at relevant
temporal and spatial scales. We also note that krill consumption by
recovering populations of krill predators provides further evidence in
support of the krill surplus hypothesis, and highlight that despite less
than comprehensive data, cetaceans are likely to consume a significant
proportion of the krill consumed by natural predators but are not
currently considered directly in the management of the krill fishery. If
management of the krill fishery is to be precautionary and operate in a
way that minimises the risks to krill predator populations, it will be
necessary in future analyses, to include up-to-date and precise abundance
and consumption estimates for pack-ice seals, finfish, squid, and other
baleen whale species not currently considered.