High‐frequency aerial surveys inform the seasonal distribution of Cook Inlet beluga whales

Abstract

Management options to mitigate potential effects from the overlap of anthropogenic and marine mammal activities require understanding of species' habitat use and movement patterns. We analyzed high temporal frequency industrial marine mammal monitoring program aerial surveys conducted over a protracted period from April to October of 2013 and 2014 to examine beluga whale (Delphinapterus leucas) ecology in the Cook Inlet, Alaska, USA. Our objectives were to characterize the spatiotemporal whale distributions, determine the utility of these patterns to inform management practices, and assess industrial survey data as a supplement to agency population monitoring programs. Cook Inlet beluga whale densities peaked in late June to early July, with some activity observed in all survey months. Consistent trends in spatial persistence were identified and found to be associated with the seasonal sequence of prey field distributions including eulachon (Thaleichthys pacificus), Pacific salmon (Oncorhynchus spp.), and gadids (Gadidae spp.). Seasonal beluga whale distributions were stable across both study years, indicating hotspots of habitat use with predictable seasonal timing. The regular temporal and spatial distribution of beluga whale activity suggests potential to inform management efforts to mitigate disturbance of whales from anthropogenic activities in the Inlet. We found high-frequency surveys conducted as part of industrial marine mammal monitoring programs provided a useful additional data source for population monitoring; however, improvements in survey design and efforts to control for observer detection biases may further increase the utility of these surveys to complement ongoing standardized scientific surveys. Ó

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

“…The %DPH during summer was in accordance with the previously reported general concentration of whales in the upper inlet, particularly near coastal mudflats and river mouths (Calkins 1989, Smith & Martin 1994, Goetz et al 2007, Hobbs et al 2005, Shelden et al 2015, Wolf et al 2018. Eagle Bay (primarily influenced by Eagle River), Little Susitna, and Beluga River were the 3 river locations we monitored in the upper inlet, and their median %DPH (2.5, 2.3, and 0.6%, respectively) were greater than all other locations (range: 0.0−0.5%) (Fig.…”

“…Foraging buzzes were not detected past July at Beluga River (during the summer), yet were detected during August and September in Eagle Bay, suggesting that the whales' preferred feeding habitat shifted from the Susitna Delta region into Knik Arm by late summer. Recent results from aerial surveys conducted in 2013 and 2014 during the open water season (April−October), conducted by Apache Alaska Corporation as part of their marine mammal monitoring protocols, provided a similar distribution of beluga concentration areas, with a strong relationship to the availability and distribution of fish prey species (Wolf et al 2018).…”

Beluga whale (Delphinapterus leucas) acoustic foraging behavior and applications for long term monitoring

“…Beluga DPH followed an expected continued presence throughout the sampled period of May to September with two typical peak periods, one in spring and another in mid-summer, followed by a decreasing trend by late summer and early fall matching previous descriptions e.g., [ 30 , 55 , 86 ]. Belugas were detected almost every day from the first day of sampling in May.…”