CI Beluga Feeding Habitat
CI belugas are frequently seen aggregating near the mouths of rivers and streams, when anadromous fish species are present and often at their peak availability (Moore et al. 2000). These concentrations of belugas within discrete areas of the upper Inlet and offshore of several important salmon streams are assumed to be the result of a feeding strategy that takes advantage of the bathymetry of the area: the fish are funneled into the channels formed by the river mouths, and the shallow waters act as a gauntlet for fish as they move past waiting belugas. Hazard (1988) hypothesized that belugas were more successful feeding in rivers where prey were concentrated than in bays where prey were dispersed, implying that CI belugas seek areas where anadromous prey escapement (return to freshwater spawning habitat) numbers are high, but also areas that have certain habitat features. Research by Frost et al. (1983) on belugas in Bristol Bay suggested those whales preferred certain streams for feeding based on the configuration of the stream channel. Their study theorized beluga feeding efficiency improved in relatively shallow channels where fish were confined or concentrated. Because belugas do not always feed at the streams with the largest runs of fish, bathymetry, fish density, and lack of disturbance may be more important than sheer numbers of fish in determining their feeding success. For example, CI belugas today are seen less frequently at the mouth of the Kenai River than they were historically, despite large salmon returns to the river. Whether this is due to changes in prey species composition or density, bathymetric changes, increased levels of disturbance, or other unknown factors remains a matter of speculation.
Habitat use in the summer months consists of semi-predictable movements of groups of belugas between river mouths and shallow tidal flats in the upper Inlet. These movements are largely cued to physical conditions, especially tide, but may also be influenced by anthropogenic activities. TEK indicates that daily movements are determined by the ebb and flow of the tide and the related movements and size of fish runs, and also by the presence of killer whales (Huntington 2000). For example, whales often concentrate on the shallow mudflats of the Susitna River Delta and Chickaloon Bay at low tide, and may enter upper Inlet rivers on the flooding tide, although the reverse tidal pattern has been observed in Eagle River in Knik Arm (T. McGuire, LGL, pers. obs.). Observational studies (Funk et al. 2005; Markowitz and McGuire 2007) and ocean circulation and inundation models, combined with tracks from tagged individual whales (Ezer et al. 2008), confirm long-held local knowledge that daily feeding movements are influenced greatly by tidal cycle.
In the fall, as anadromous fish runs begin to decline, belugas consume the fish species found in nearshore bays and estuaries; however, some belugas may feed on salmon kelts (spawned fish) during this time. Habitat associations of nonanadromous beluga prey species in Cook Inlet include preferences for sand and mud substrates (Eschmeyer et al. 1983; Cohen et al. 1990; ADF&G 2004), and a number of these species move seasonally from shallow to deep water. Movements of belugas within the Inlet during the months when anadromous fish runs are not present may reflect the seasonal movements of these other prey species. Unlike salmon and eulachon, the prey available in winter do not tend to form large concentrations, and it may be that belugas tend to disperse throughout the Inlet during November through April, to utilize the more-dispersed prey (Hobbs et al. 2005). In the winter, CI belugas use deeper waters in the mid Inlet past Kalgin Island and make deep feeding dives. The presence of Kalgin Island south of the Forelands may create upwelling and eddies which concentrate nutrients and provides a still-water refuge area for migrating anadromous fishes (Calkins 1983, 1989). This area may also be a late- winter staging area for eulachon before they return to streams in the upper Inlet. Given the unique oceanographic conditions and the diversity of fish and crustaceans found near Kalgin Island, this area may be rich in biological productivity, and thus an important winter feeding habitat for belugas.
Castellote et al. (2016a) obtained information on the seasonal distribution and foraging behavior of belugas in Cook Inlet through passive acoustic monitoring of beluga social calls and echolocation activity at 13 locations in lower Cook Inlet (Homer, Tuxedni Bay, and Kenai River), upper Cook Inlet (Trading Bay, Beluga River, Little Susitna River, and Fire Island), and Knik Arm (Point Mackenzie, Cairn Point, Six Mile, South Eagle Bay, Eagle River Mouth, and North Eagle Bay) during 2008–2013. Analysis of the echolocation data indicated that foraging behavior, as inferred from presumed foraging buzzes, was more prevalent during summer than during winter, particularly at upper Inlet rivers. Passive acoustic monitoring was restricted to nearshore areas, so offshore foraging was not assessed, and due to a limitation of the study methods, foraging on benthic prey may not have been readily detectable.
Goetz et al. (2007, 2012b) used geographic information systems (GIS) to develop quantitative models of the summer habitat preferences of CI belugas. Habitat models were used to examine ecological relationships among belugas and several environmental variables. Parameters used in the models were based on June/July beluga sightings (1993 to 2004) relative to available environmental data: 1) bathymetry; 2) mudflats; and 3) flow rates among freshwater tributaries entering Cook Inlet. The two quantitative models predicted similar size and location of beluga habitat and identified mudflats and river size as important environmental features. Belugas are found near mudflats and prefer medium and high flow accumulation areas (i.e., medium to large river basins). Although sighting data in this study were collected primarily in June, other aerial surveys (Rugh et al. 2000, 2004), shore-based systematic and opportunistic observations (Funk et al. 2005; NMFS, AFSC MML, unpub. data), boat-based photo- identification surveys (McGuire and Bourdon 2012), and whales tagged with satellite transmitters (Hobbs et al. 2005) show that the distribution documented in June is largely representative of the distribution throughout the ice-free months; Knik Arm, Turnagain Arm, Chickaloon River, and the Susitna River Delta are used extensively. In fact, belugas occasionally access these preferred habitats in winter despite thick ice cover (Hobbs et al. 2005). Tidal movement corridors are also important to CI belugas, as beluga movements with the tides may occur up to twice daily and allow or limit access to feeding areas (Hobbs et al. 2005; Funk et al. 2005; Markowitz and McGuire 2007). Access to these areas and to corridors between these areas is important to the feeding strategy of CI belugas.
Additional analyses by Goetz et al. (2012b) concluded that belugas were found in areas of high fish availability and access to tidal flats and sandy substrates and that belugas were negatively associated with anthropogenic disturbance. These habitat models predicted that beluga distribution would include coastal areas extending nearly the entire length of Cook Inlet (Goetz et al. 2007), and, historically belugas inhabited large parts of the Inlet, including its central and southern reaches (Rugh et al. 2000). However, since 1993, beluga sightings have been rare (0–4% of all reported sightings per year) in areas south of the Forelands, and almost all sightings have been in the upper Inlet, from the Susitna Delta to Knik Arm and Chickaloon Bay (Rugh et al. 2000, 2005a, b). A significantly reduced CI beluga population (Hobbs et al. 2000), in combination with beluga preference for estuarine waters with the largest concentration of prey species, may explain the current distribution of whales, but data on relative densities of fish by species and season are not available to test this hypothesis.
CI Beluga Calving Habitat
In addition to being important feeding habitats, the shallow waters of the upper Inlet may also play important roles in reproduction. Since newborn belugas do not have the thick blubber layer of adults, they may benefit from the warmer water temperatures in the shallow tidal flats areas where fresh water empties into the Inlet, and it is likely these regions are used as nursery areas (Katona et al. 1983; Calkins 1989). These shallow areas may also provide refuge from killer whale predation on calves. The TEK of Alaska Natives has described historical beluga calving and nursery habitats as the northern side of Kachemak Bay, the mouths of the Beluga and Susitna Rivers, as well as Chickaloon Bay and Turnagain Arm (Huntington 2000). Knik Arm is also used extensively in the late summer and fall by cow/calf pairs: Funk et al. (2005) noted a relatively high representation of calves in the uppermost part of Knik Arm; the mouth of Knik Arm has been reported to be transited in the summer and fall by cow/calf pairs (Cornick and Kendall 2008); and groups seen in Eagle Bay usually contain calves (McGuire and Bourdon 2012).
Because calving events have not been documented in Cook Inlet, specific calving grounds have not been identified, although it seems likely that the areas identified as nursery areas might also serve as calving grounds. Based on the presence of calves sighted in summer aerial surveys, Calkins (1983) speculated that calving might occur in the larger estuaries of upper western Cook Inlet. During boat-based surveys for calves conducted in 2007 to 2011, the first neonates (i.e., newborns) of the season were seen at the Susitna River Delta (McGuire and Bourdon 2012). Later in the season, groups seen in Knik Arm were more likely to contain neonates than groups in other areas. Distinct areas for neonate and calf rearing were not identified, as calves and neonates were seen in all locations surveyed in upper Cook Inlet (the Susitna River Delta, Knik Arm, Chickaloon Bay/Southeast Fire Island, and Turnagain Arm). McGuire et al. (2016) reported that during photo-identification surveys conducted in upper Cook Inlet (2005 to 2015) and the Kenai River Delta (2011 to 2013), the first neonates seen each survey year were located in the waters of the Susitna River Delta. Neonates were seen later in the season in all other survey areas where belugas were encountered (i.e., the Susitna River Delta, Knik Arm, Chickaloon Bay, Turnagain Arm, and the Kenai River). McGuire et al. (2016) also documented the birth of a CI beluga in the Susitna River Delta. Based on these data, they suggested the Susitna River Delta should be considered a calving ground for CI belugas, and the nearshore waters of upper Cook Inlet should be considered CI beluga nursery grounds.
Other Uses of Habitat
Other important uses of habitat by CI belugas may include avoidance/escape from predators, transiting among feeding and/or nursery habitats, refuge from human activities (e.g., in-water noise, ship traffic, and hunting), and molting. In the 2008 Conservation Plan (NMFS 2008a), NMFS stated that warmer, fresher coastal waters may be important areas for belugas’ seasonal summer molt (Finley 1982) and that shallow waters may provide conditions necessary to help facilitate the shedding of dead skin and regeneration of epidermal layers. However, eight years of photographic records of over 303 individual CI belugas photographed from April to November do not display signs of obvious molting; it may be that molting in CI belugas is a more diffuse, gradual process than it is for those beluga stocks found in more northern latitudes and that habitat specifically for seasonal molting is not required for CI belugas. Molting has also not been observed in SLE belugas, despite over 25 years of studies on this population (P. Béland, St. Lawrence National Institute of Ecotoxicology, pers. obs.).
Human Environment of Cook Inlet
Belugas in Cook Inlet are unique in Alaska given that their habitat is in close proximity to the largest urban area in the state with over 60% of the state-wide population. In 2010 (the most recent census year available), the population of the State of Alaska was 710,231 people, with 291,826 in the Municipality of Anchorage, 88,995 in the Matanuska-Susitna Borough, and 55,400 in Kenai Peninsula Borough. The population in this region has been increasing; between 1980 and 2010 the population grew by 67%.
Belugas are not uniformly distributed throughout Cook Inlet, but are predominately found in nearshore waters, adjacent to areas of high human activity. Humans use the waters and shores of Cook Inlet for fishing, hunting, recreating, timber harvesting, mining, shipping, dredging, renewable energy production, discharge of wastewater, military activities, oil and gas development, transportation, and residential and industrial development (Figure 11).
The majority of land in the Cook Inlet Basin is publicly managed by state or federal agencies. Native groups and individuals are among the most significant private landowners.