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MEPS prepress abstract   -  DOI:

The role of sea ice in the distribution, habitat use, and phenology of eastern North Pacific gray whales

Trevor W. Joyce*, Megan C. Ferguson, Catherine L. Berchok, Dana L. Wright, Jessica L. Crance, Eric K. Braen, Tomoharu Eguchi, Wayne L. Perryman, David W. Weller

*Corresponding author:

ABSTRACT: A strong negative relationship has been observed between calf production of Eastern North Pacific gray whales Eschrichtius robustus and Pacific Arctic sea ice area (except in 2 potentially anomalous periods: 2013–2014 and 2017–2019). Sea ice may play a role in reproductive variability by blocking gray whale access to foraging hotspot habitats. We tested this “sea ice exclusion” hypothesis using on complementary aerial survey and moored hydrophone datasets, that together provide broad spatial and temporal coverage, respectively. A negative relationship (GAM, p < 0.001) was found between gray whale aerial counts and ice concentration in the northeast Chukchi Sea (2008-2019), with a nonlinear increase in negative slope above 45-55% concentration. A comparison of distribution patterns between years further indicated the absence of sightings within northern Bering and northeastern Chukchi foraging hotspots during years with delayed ice break-up versus years with an early-to-average ice retreat. Passive acoustic recordings likewise showed the near-absence of detections during periods of dense ice cover, and indicated a strongly positive relationship between ice break-up dates and the timing of acoustic detection onset. Together these analyses point to the important role of sea ice in gray whale distribution, habitat use, and phenology. However, a relatively consistent 10-15 day lag observed between ice break-up and acoustic onset dates, suggested that the mechanism(s) underpinning gray whale interactions with sea ice may be more complex than simply ‘sea ice exclusion.’ Here we propose ‘prey quality timing’ as a potential alternative hypothesis that warrants further investigation.