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Seasonal distribution and foraging occurrence of Cook Inlet beluga whales based on passive acoustic monitoring

Manuel Castellote*, Robert J. Small, Marc O. Lammers, Justin Jenniges, Jeffrey Mondragon, Christopher D. Garner, Shannon Atkinson, Jade Delevaux, Richard Graham, Delmar Westerholt

*Corresponding author:

ABSTRACT: A paucity of information on the basic biology and ecology of Cook Inlet beluga whales Delphinapterus leucas remains a decade after the species was listed as endangered in 2008. The causes of its continued decline remain unclear. This lack of knowledge limits our understanding of, and ability to manage, potential threats impeding the recovery of this endangered population. Seasonal distribution and foraging ecology, particularly during winter, are currently among the most basic gaps in knowledge. Thus, we conducted a year-round passive acoustic monitoring program from 2008–2013, monitoring 13 locations within critical habitat. We identified seasonal occurrence patterns across years at most locations. Detections were higher in the upper inlet during summer, peaking in known concentration areas. The occurrence of whales in the upper inlet when ice coverage peaked during winter was more prevalent than previously suggested. We documented seasonal differences in foraging habitat preference, with foraging behavior more prevalent during summer, particularly near upper inlet rivers, than during winter. Foraging peaks corresponded with the presence of different anadromous fish runs from spring to fall. Low levels of feeding activity in winter suggest a lack of feeding aggregation areas, feeding in non-monitored offshore waters, or increased effort on benthic prey. These results represent a substantial contribution of Cook Inlet beluga seasonal distribution and foraging ecology, which will strengthen conservation and management strategies and thus more effectively promote recovery of this endangered population.