Beluga Distribution in Cook Inlet
Data on distribution and habitat use comes primarily from two main sources: aerial surveys (Hansen and Hubbard 1999; Speckman and Piatt 2000; Rugh et al. 2010; Shelden et al. 2015b) and satellite transmitter tagging studies during August through March (Hobbs et al. 2005). Additional information is provided by traditional ecological knowledge (TEK) of Alaska Natives (e.g., Huntington 2000; Braun and Huntington 2011; Carter and Neilsen 2011), boat and land- based observations (e.g., McGuire and Bourdon 2012; Brueggeman et al. 2013), passive acoustic monitoring studies (e.g., Small 2011), opportunistic reports (e.g., Rugh et al. 2000; Vate- Bratstrom et al. 2010; Shelden et al. 2015b; NMFS, unpub. data), NMFS stranding records (e.g., Vos and Shelden 2005; NMFS, unpub. data), and data from a citizen science CI beluga sighting project (Švarný Carlson et al. 2015).
Localized information on distribution and habitat use of specific areas of Cook Inlet is available from studies conducted in conjunction with the development activities, universities, or other entities. Some of the available data sources are associated with: the Port of Anchorage Expansion Project; Ocean Renewable Power Company’s Fire Island Tidal Project; Pac-Rim Coal’s Chuitna Coal Project; Cook Inlet Region Inc.’s Fire Island Wind Project; the Alaska Department of Transportation’s Seward Highway Expansion Project; the Port MacKenzie Expansion Project; the Knik Arm Bridge and Toll Authority’s (KABATA) Knik Arm Crossing; the Alaska Communication System’s Fiber Optic Cable Project; seismic programs for Apache Alaska, ConocoPhillips Alaska, and Furie/Escopeta Oil; Joint Base Elmendorf Richardson’s CI beluga studies program; and LGL’s CI beluga Photo-Identification Project. Many of these projects’ reports may be found on the NMFS AKR website.
Distribution Patterns: 1970s, 1990s, and 2000s
The distribution of CI belugas has changed significantly since the 1970s, when aerial surveys for belugas in Cook Inlet were first conducted. ADF&G conducted aerial surveys of Cook Inlet in June and July in the late 1970s. These surveys were limited in scope and involved a single sample of a portion of Cook Inlet. While many of the early reports lacked sufficient descriptions of how and where the surveys occurred, good documentation is available for aerial surveys conducted on 18 June 1978 and 18–22 June 1979 (ADF&G, unpub. data). Beginning in 1993 NMFS started conducting comprehensive surveys annually (with the exception of 2013 when surveys were switched to a biennial schedule) during a 1- to 2-week period each year[For more information, contact the NMFS AFSC MML, Cetacean Assessment and Ecology Program.], with 3–7 repetitions of coastal flights around the upper Inlet plus 1–2 days dedicated to a survey of the lower Inlet (Rugh et al. 2000, 2005a,b; Hobbs et al. 2015a; Alaska Fisheries Science Center, Marine Mammal Laboratory [AFSC MML], unpub. data).
Rugh et al. (2010) used three time periods to examine changes in historical distribution patterns of CI belugas: late 1978 to 1979 (when well-documented data are available; Figure 6); 1993 to 1997 (during a decline in abundance; Figure 7); and 1998 to 2008 (when hunting was regulated and recovery was anticipated; Figure 8). This analysis of aerial survey data showed that the extent of the late spring/early summer distribution (June/July) of CI belugas has changed considerably since the late 1970s. The whales were distributed over a relatively large area in 1978 and 1979, with the central location of the summer range occurring between the McArthur and Beluga rivers (Figure 6). The area of highest concentration included the region from Drift River to the Susitna Delta. The TEK also indicated that CI belugas had long been observed in the lower Inlet, including Kachemak Bay on the eastern side and Tuxedni and Trading Bays on the western side, although rarely in large numbers (Huntington 2000; Braund and Huntington 2011). From 1993 to 1997, the central location of the summer range shifted northeast to the mouth of the Susitna River and the area of highest concentration contracted to a region north of Moose Point (Figure 7). From 1998 to 2008, the central location of the summer range shifted east, then occurring between the Little Susitna River and Fire Island (Figure 8); the area of highest concentration included Knik Arm and Chickaloon Bay (between Point Possession and Turnagain Arm). Changes in distribution over the three time periods were significant. These include the northeast contraction of the summer range of belugas into upper Cook Inlet from the 1970s to the 1990s and into the 2000s, as well as a longitudinal shift east toward Anchorage between 1993 and 2008. Core summer distribution was estimated to have contracted from over 7,000 km2 (2,703 mi2) in 1978 to 1979, to 2,800 km2 (1,081 mi2) in 1998 to 2008 (Rugh et al. 2010).
Subsequent to this analysis, Shelden et al. (2015b) compared the core summer distributions reported for the three time periods examined by Rugh et al. (2010) (Figures 6, 7, 8) with the core summer distribution of CI belugas observed in 2009 to 2014 (Figure 9). In this more recent time period, the core summer distribution (estimated area = 1,787 km2) continued to contract northward, while remaining centered on the Susitna Delta (Figure 9). Fewer sightings of CI belugas in lower Cook Inlet in recent decades (Hansen and Hubbard 1999; Speckman and Piatt 2000; Rugh et al. 2000, 2004, 2010) also indicate that the summer range of CI belugas has contracted to the mid and upper Inlet, coincident with their decline in population size.
The reason for this change of distribution is not known, but several hypotheses have been proposed, including: 1) an effect of changing habitat, such as through diminished prey availability (Moore et al. 2000); 2) avoidance of killer whales (Shelden et al. 2003); and 3) preference and ability of this remnant population to remain in preferred habitat areas due to reduced intra-specific competition as a result of a reduction in population size (Goetz et al. 2007). Regardless of the reason, the result of the CI beluga range contraction brings animals in a small range proximal to Anchorage during summer months, where there is increased potential for disturbance from human activities.
Seasonal Distribution Patterns
Multiple data sources indicate that belugas exhibit seasonal shifts in distribution and habitat use within Cook Inlet, however, belugas in Cook Inlet do not migrate out of Cook Inlet. The known seasonal shifts in distribution of CI belugas appear to be related to seasonal changes in the physical environment (e.g., ice and currents) and to shifts in food sources, specifically the timing of fish runs. Generally, CI belugas spend the ice-free months in the upper Inlet (often at discrete high-use areas), then expand their distribution south and into more offshore waters of the middle Inlet in winter (Hobbs et al. 2005), although they may be found throughout the Inlet at any time of year. These seasonal patterns have been long observed and utilized by subsistence hunters (Huntington 2000), and as reviewed by Shelden et al. (2015b), have more recently been documented by aerial surveys (Rugh et al. 2000, 2004), satellite telemetry (Ferraro et al. 2000; Hobbs et al. 2005), and during shore and boat-based observations (e.g., Funk et al. 2005; McGuire and Bourdon 2012; McGuire et al. 2014a). Most recently, passive acoustic monitoring is being used to assess seasonal movements throughout the Inlet (Lammers et al. 2013; Castellote et al. 2016a).
Movement data are available from 14 CI belugas tracked for variable periods of time (2–240 days) with satellite transmitters between May 1999 and March 2003. Tags attached to nine whales logged movements from August or September into December, with four continuing to transmit movement data into the following March (Hobbs et al. 2005; Goetz et al. 2012a; Shelden et al. 2015b). All tagged CI belugas remained within Cook Inlet for the period they were tracked. Whales spent the summer and early fall months in the upper Inlet, concentrating at river mouths. Within this time period, whales often made weekly movements between the mouth of the Little Susitna River, Knik Arm, Turnagain Arm, and Chickaloon Bay.
During the late summer the belugas remained in the upper Inlet, centered in Knik Arm (Figures 10a, 10b). During the fall, the belugas concentrated in Chickaloon Bay and areas of the west side near Tyonek (Figures 10c, 10d). In late fall, tagged whales began to make more extensive movements south into the middle Inlet and into deeper offshore waters (Figure 10e), and were not found in the large dense groups commonly seen in the summer months (Rugh et al. 2004). This pattern continued through winter (Figures 10f–10h), when whales exhibited the most wide-ranging movements, spanning both nearshore and offshore waters from the upper reaches of Knik Arm to the middle Inlet.
Several other observational studies have been conducted which contribute to our understanding of CI belugas’ seasonal movements. A year-round shore and boat-based observational study in Knik Arm (July 2004 to July 2005) revealed seasonal patterns in habitat use and abundance of this area, with peak abundances in fall (September) declining to lowest numbers in winter, and highest use of river mouths and mud flats (Funk et al. 2005). Shore-based studies during the ice-free months along Turnagain Arm found peak beluga abundances mid- August through October, with whales occasionally present mid-April to early May (Markowitz and McGuire 2007; McGuire and Bourdon 2012). An ongoing (2005–present) photo- identification study within the upper Inlet with sighting histories of 376 individual belugas (2005–2015; T. McGuire, LGL Alaska Research Associates [LGL], pers. obs.) has documented movements by individual whales among several high-use areas within a summer season, including Susitna Flats, Knik Arm, Chickaloon Bay, Turnagain Arm (McGuire et al. 2009), and the Kenai River (McGuire et al. 2014a). Results from passive acoustic monitoring across the entire Inlet (summarized in Section II.B.4. Use of Critical Habitat by Belugas) support seasonal patterns observed with other methods (M. Castellote et al., AFSC MML, pers. comm.).
Large aggregations of belugas in specific areas of upper Cook Inlet during May to October are presumed to indicate a critical time period for foraging, based on the need to assimilate resources for overwinter survival (Calkins 1983; Huntington 2000). It is during the ice-free months when calves are born and nursed and when the whales acquire the thick blubber layer they will need to survive through the winter months, when anadromous fish runs end and prey move to deeper, offshore regions (Hobbs et al. 2005; Hobbs et al. 2008).