Passive acoustic monitoring off Vancouver Island reveals extensive use by at-risk Resident killer whale (Orcinus orca) populations

Abstract

Two sympatric populations of fish-eating Resident killer whales inhabit the coastal waters of British Columbia, Canada: Southern and Northern Resident killer whales. These populations are listed under Canada's Species at Risk Act (SARA) as 'endangered' and 'threatened', respectively. Relatively little is known about their habitat use outside of the sheltered waters along the east coast of Vancouver Island, especially during the winter. SARA requires the identification of critical habitat for these populations. High densities of Chinook salmon-their primary preyare found around Swiftsure Bank, an area identified as potential critical habitat for Southern Residents. However, it is a difficult area to survey for whales using conventional small-boat approaches. Here, we used 2 yr of data collected from an autonomous acoustic recorder deployed at Swiftsure Bank from 2009−2011 to assess the year-round habitat use of this area by Resident killer whales. Overall, Resident killer whales were detected on 244 of 680 monitored days (36%). Southern Residents were heard in all months, with activity peaking during the summer. Northern Residents were also heard throughout the year, but were mostly detected in the spring and fall, which indicates the 2 populations may differ in their strategies for using this common foraging area. High levels of use by both of these populations highlights the importance of Swiftsure Bank to both, supporting the expansion of Resident killer whale critical habitat to include this site.

Survival of the fattest: linking body condition to prey availability and survivorship of killer whales

“…However, L pod spends more time during the summer months in the western strait of Juan de Fuca than J or K pods (Riera et al. 2019) and may be targeting Puget Sound Chinook as they migrate from their open ocean phase toward spawning tributaries. The somewhat unique oceanic distribution of Puget Sound Chinook along the west coast of Vancouver Island (Weitkamp 2010, Shelton et al.…”

“…This is surprising, given that L pod is rarely in Puget Sound in the summer and spends less time in adjacent inland waters during the summer months than J or K pods (Riera et al. 2019), and Puget Sound origin Chinook are generally smaller and less numerically dominant than other stocks (O'Neill et al. 2014, Pacific Fishery Management Council 2020).…”

“…2009), and we considered each pod separately in our analyses based on previously described differences in range and movement patterns (National Marine Fisheries Service 2019, Riera et al. 2019).…”

Endangered predators and endangered prey: Seasonal diet of Southern Resident killer whales

“…SRKWs and northern resident killer whales have been shown to be salmon specialists, with a strong selectivity for Chinook salmon [8][9][10][11]. These two adjacent, partially overlapping populations [66] potentially consume many of the same Chinook salmon stocks as most of these stocks migrate north following ocean emergence [59] before returning south to their natal rivers as adults. Limited diet data are available for NRKWs apart from summer data [67] that indicated this population to be consuming a similar number of stocks in summer [68] as SRKWs consumed in winter (this study, see Supplemental tables).…”

Distribution and Habitat Preferences of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) Inhabiting Coastal Waters With Mixed Levels of Protection

“…However, inshore habitats are likely to contain tiger sharks (Andrzejacek et al, 2019). Information on the likelihood of encountering a predator and how this may influence IP bottlenose dolphin occurrence should be a topic of future research at the NWC and could be obtained through Baited Remote Underwater Video Surveys (BRUVS) in shallow coastal lagoons (e.g., Espinoza et al, 2014), or through acoustic monitoring (e.g., Braccini et al, 2017;Riera et al, 2019).…”