Empirically testing the influence of light regime on diel activity patterns in a marine predator reveals complex interacting factors shaping behaviour

• Published in: Functional Ecology
• Main Authors: Storrie, Luke, Hussey, Nigel E., MacPhee, Shannon A., O'Corry-Crowe, Greg, Iacozza, John, Barber, David G., Loseto, Lisa L.
• Format: Text
• Language: unknown
• Published: Scholarship at UWindsor 2022
• Subjects: Arctic; Central Arctic Ocean; diel vertical migration; diurnal; dive; natural experiment; nocturnal; whale; Integrative Biology; Arctic Ocean; Beluga; Beluga*; Delphinapterus leucas; polar night; Sea ice; midnight sun
• Online Access: https://scholar.uwindsor.ca/ibiopub/182; https://doi.org/10.1111/1365-2435.14172; https://scholar.uwindsor.ca/context/ibiopub/article/1181/viewcontent/Functional_Ecology___2022___Storrie___Empirically_testing_the_influence_of_light_regime_on_diel_activity_patterns_in_a.pdf

Diel cycles in marine predator diving behaviour centre around the light-mediated diel vertical migration (DVM) of prey, and are considered critical for optimizing foraging and limiting competition across global seascapes. Yet, our understanding of predator diel behaviour is based primarily on examining relative depth usage between constant day/night cycles with no formal investigation of how varying light regimes interact with abiotic factors to shape diel activity. The extreme seasonal light regimes (midnight sun, polar night, day/night cycle) in the Arctic provide a unique natural experimental setting to empirically investigate the occurrence and intensity of diel behaviour in marine predators relative to changing light levels while concomitantly assessing interacting abiotic factors. Depth time series data from satellite-linked tags deployed on six beluga whales (Delphinapterus leucas) for up to 12 months were used to quantify diel behaviour by calculating dissimilarity in time-at-depth between periods of low and high solar altitude on each day. Generalized additive mixed effects models were used to examine the influence of hours of daylight across extreme light cycles, coupled with bathymetry and sea ice concentration; focal diel patterns were further examined relative to the thermal structure of the water column. As predicted, belugas exhibited cathemerality during the midnight sun, and initiated diel behaviour with the onset of the fall day/night cycle, with a marked increase in its intensity with the progression to equal day/night length. Occurrence of diel patterns, however, was complex; ceasing in regions with seafloor depths <700 >m, and occurring with greatest intensity when the water column was thermally homogeneous within the upper 150 m. Through empirical investigation, this study demonstrates that the onset of day/night light cycles and presumably associated prey DVM can modulate predator diel dive behaviour under certain circumstances, but highlights how the complex interaction of abiotic ...