‘Whale wave’: shifting strategies structure the complex use of critical fjord habitat by humpbacks
AUTHORS: ERIC M. KEEN, JANIE WRAY, HERMANN MEUTER, KIM-LY THOMPSON, JAY P. BARLOW, CHRIS R. PICARD (2017)
PUBLICATION: Inter-Research Science Publisher
ABSTRACT: A decade of visual surveys (2005-2014) revealed that humpbacks Megaptera novaeangliae occupy a temperate fjord system in British Columbia, Canada, in a wave pattern that propagates from outer channels in the summer to deep inland channels in late fall. Monte Carlo randomization confirmed this apparent pattern statistically. ‘Before’ and ‘after’ shift phases were most evident in July and October, respectively. We hypothesized that the ‘whale wave’ was being driven by (1) prey following, (2) the tracking of environmental proxies, (3) fine-scale philopatry, or some combination of these three factors. To evaluate these hypotheses, we collected new data in 2015, including visual and hydroacoustic surveys and oceanographic sampling. To both full-season and monthly datasets, we fit generalized additive models (GAMs) in a stepwise procedure, using variable sets that represent our hypotheses. Prey models were generally the worst predictors of humpback distribution, while the most complex habitat models were the best. The Prey model performed best in June but increasingly poorly in remaining months. The performance of all models declined throughout the season, suggesting not only that this whale wave is being driven by needs other than food, but also that untested variable(s) inform late-season distribution. Alternative explanations of the wave include physiological maintenance and social habitat partitioning. Our findings demonstrate that marine predators can use complex spatial strategies not only to navigate vast areas of ocean but also to exploit specific habitats thoroughly. Though annually persistent and specific in structure, the whale wave would go (and has gone) unnoticed in typical marine mammal surveys.
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