Data from: The nightscape of the Arctic winter shapes the diving behavior of a pelagic predator

Predator-prey interactions in marine ecosystems are dynamically structured
by light, which is exemplified by diel vertical migrations of low-trophic
level organisms. At high latitudes, the long winter nights provide
foraging opportunities for marine predators targeting vertically migrating
prey closer to the surface at night while minimizing energy expenditure,
but there is limited documentation of such diel patterns under extreme
light regimes. To address this knowledge gap, we recorded the diving
behavior of 17 harbour porpoises just south of the Arctic circle in West
Greenland, from summer to winter. Unlike classical diel vertical
migration, the porpoises dove three times deeper at night and the
frequency of deep dives (>100 m) increased tenfold as they entered
the darkest months. The daily mean depth was negatively correlated with
daylength, confirming this reverse diel migration and suggesting an
increased activity—presumably to target prey at greater depths—when
approaching the polar night. Our findings illustrate a light-mediated
strategy in which harbour porpoises would maximize energy gain during long
periods of darkness while minimizing energy expenditure by accessing
vertically migrating prey, which are otherwise inaccessible in deep
waters. Extreme light regimes observed at high latitudes are therefore
critical in structuring pelagic communities and food webs.