Using predicted patterns of 3D prey distribution to map king penguin foraging habitat
Résumé
King penguins (Aptenodytes patagonicus) are an iconic Southern Ocean species, but
the prey distributions that underpin their at-sea foraging tracks and diving behaviour
remain unclear. We conducted simultaneous acoustic surveys off South Georgia and
tracking of king penguins breeding ashore there in Austral summer 2017 to gain insight
into habitat use and foraging behaviour. Acoustic surveys revealed ubiquitous deep
scattering layers (DSLs; acoustically detected layers of fish and other micronekton that
inhabit the mesopelagic zone) at c. 500 m and shallower ephemeral fish schools. Based
on DNA extracted from penguin faecal samples, these schools were likely comprised of
lanternfish (an important component of king penguin diets), icefish (Channichthyidae
spp.) and painted noties (Lepidonotothen larseni). Penguins did not dive as deep
as DSLs, but their prey-encounter depth-distributions, as revealed by biologging,
overlapped at fine scale (10s of m) with depths of acoustically detected fish schools.
We used neural networks to predict local scale (10 km) fish echo intensity and depth
distribution at penguin dive locations based on environmental correlates, and developed
models of habitat use. Habitat modelling revealed that king penguins preferentially
foraged at locations predicted to have shallow and dense (high acoustic energy) fish
schools associated with shallow and dense DSLs. These associations could be used to
predict the distribution of king penguins from other colonies at South Georgia for which
no tracking data are available, and to identify areas of potential ecological significance
within the South Georgia and the South Sandwich Islands marine protected area.