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

M Castellote,J Jenniges,Jms Delevaux,Rj Small,S Atkinson,D Westerholt,R Graham,J Mondragon,Cd Garner,Mo Lammers

doi:10.3354/esr01023

Abstract

A paucity of information on the basic biology and ecology of Cook Inlet beluga whalesDelphinapterus leucasremains 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. Therefore, we conducted a year-round passive acoustic monitoring program from 2008-2013, monitoring 13 locations within the belugas’ 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 coincided 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 to our knowledge 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.

Highlights

Of the 5 populations of beluga whale Delphinapterus leucas recognized by US NOAA Fisheries in Alaska, the most isolated is in Cook Inlet (Hill & DeMaster 1998)
When the 6 locations in Knik Arm were pooled into the Eagle Bay and Lower Knik Arm areas, we considered only one acoustic effort hour (AEH) when more than one AEH occurred in the same hour among pooled locations, which resulted in 236 590 AEHs (9858 d), a 16.2% decrease
Several moorings were not recovered in the Knik Arm region in the upper inlet due to the combination of very shallow depths, strong currents, large vegetative debris suspended in the water column, high levels of sedimentation, and extensive ice gauging in winter

Summary

Introduction

Of the 5 populations of beluga whale Delphinapterus leucas recognized by US NOAA Fisheries in Alaska, the most isolated is in Cook Inlet (Hill & DeMaster 1998). There is very limited knowledge on diet for this population, mainly gained from traditional knowledge and stomach contents sampled during subsistence harvests Their main prey include several species of Pacific salmon, with coho Oncorhynchus kisutch showing the highest proportion in stomachs (but preference for sockeye Oncorhynchus nerka is listed in traditional knowledge reports), followed by cod species (Arctic cod Boreogadus saida, saffron cod Eleginus gracilis, walleye pollock Theragra chalcogramma, and Pacific cod Gadus macrochephalus), eulachon Thaleichthys pacificus, and flounder (Pleuronectidae) (Quakenbush et al 2015, Huntington 2000). There is no knowledge of winter diet or prey preferences

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Conclusion