DOI: 10.5061/dryad.fttdz08wk
title: Data from: Empirically testing the influence of light regime on diel activity patterns in a marine predator reveals complex interacting factors shaping behaviour

description: 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
 belugas 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 &lt; 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 factors with light regime shape dynamic
 spatiotemporal patterns. These findings, building on a body of recent
 work, emphasize that the traditional view of the ubiquitous occurrence of
 diel behaviour tied to DVM at the base of the food web oversimplifies
 vertical predator-prey interactions, identifying the need for more
 structured investigation. 
description: Six male beluga whales were tagged with SPLASH10-F-238
 satellite-linked transmitters (Wildlife Computers Ltd., Redmond, WA, USA)
 from Hendrickson Island, Northwest Territories, Canada, in July 2018. Tags
 collected Fastloc GPS locations and estimated Argos locations each time a
 transmission was made. Tags sampled depth at 1 s intervals and transmitted
 the data as time series in hour-long messages subsampled at 75 s
 intervals.  Locations were filtered (see Storrie et
 al., 2022), and continuous-time correlated random walk (CTCRW) models were
 used to re-estimate locations at regular 15 min intervals (Johnson et al.,
 2008). The datasets provided here are a subset of CTCRW-modeled locations
 and depth time series data for one beluga (beluga ID LC2018#3) between
 August 4th and October 30th 2018, and can be used to replicate the methods
 for identifying diel patterns in dive behaviour. R code can be downloaded
 from a GitHub repository (https://github.com/storriel/Diel_Dive_Behaviour). 
description: These are csv files, which can be opened with Microsoft Excel, a
 text editor, or a programming language such as with the R code associated
 with the manuscript (https://github.com/storriel/Diel_Dive_Behaviour).