Belugas have acute vision both in and out of the water. A beluga’s eye is particularly well adapted for seeing in water. In air, certain features of the lens and cornea correct for the nearsightedness that result from the refraction (bending) of light rays as they go from water to air. A beluga’s retinas contain both rod and cone cells, indicating that they may have the ability to see in both dim and bright light (rod cells respond to lower light levels than do cone cells). As with other whales, belugas lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for color vision than most land mammals (Peichl et al. 2001; Levenson and Dizon 2003).
Among marine mammals, adaptation to a strictly marine environment has favored a primary sensory modality based on sound production and reception (Wood 1973). Other senses, such as smell, are diminished or even absent (Caldwell and Caldwell 1972). The available sensory channels that are utilized by marine mammals are acoustic, tactual, visual, and chemical (gustatory; Caldwell and Caldwell 1977; Winn and Schneider 1977). Except for the bottlenose dolphin (Herman 1980) and California sea lion (Thomas et al. 1992), few studies have examined in any detail the sensory capabilities of marine mammals. Olfactory lobes of the brain are absent in all odontocetes, suggesting that they have no sense of smell, although these lobes are found in the embryos (Kellogg, 1958).
Some studies have noted sensory areas in beluga mouths that may function in taste (Haley 1986). There is further evidence of chemoreception in the mouth in some species including the beluga. Reports have suggested that belugas react to blood in the water by quickly retreating and showing unusual alarm. Furthermore, it has been proposed that belugas release a pheromone when alarmed (Dudzinski et al. 2002).
Throughout their distribution, belugas are extremely social animals that typically migrate, hunt, and interact together, often in dense groups. In areas of the Arctic, belugas aggregate in the hundreds and sometimes thousands (O’Corry-Crowe 2002). High group cohesion and large group sizes may provide benefits to group members in terms of information gathering and transfer with regard to resource availability (e.g., prey, calving sites, oceanographic conditions) and cooperation in predator avoidance and reduced predation risk (Hamilton 1971; Reluga and Viscido 2005). It is not known whether social structure plays a role in determining which adults are available for breeding. It is thought that the basic social units of these groups are maternal lineages of adult females and their offspring and that males migrate separately (Smith et al. 1994). Genetic evidence for Canadian stocks of belugas indicates that migration routes and summer distribution are maintained by maternal lineages (Turgeon et al. 2012); however, this information is unavailable for Cook Inlet. It is possible the strong site fidelity belugas exhibit may be learned during the period of dependence when the mother teaches the weaning calf to forage.
In Cook Inlet, groups of four to 250 belugas have been observed during the ice-free months, and single whales are only occasionally seen (McGuire and Bourdon 2012; T. McGuire, LGL, pers. comm.). It is not known if groups represent distinct social divisions. Preliminary results from photo-identification research indicate beluga groups in upper Cook Inlet during the ice-free months of the field season are mixed and homogenous, without evident long-term sub groupings (McGuire et al. 2011). That is, there do not appear to be distinct groups consisting of CI belugas of the same gender or ages, and the available information suggest individual belugas spend time with different groups of belugas, many of which are found in all or several of the regions surveyed by the photo-identification project. Information on beluga social structure during months with ice and for groups found in the lower Inlet does not currently exist. Studies of beluga groups in the Kenai River and its vicinity were conducted 2011–2013 and indicate these are the same individuals that use the upper Inlet, with the same fluid social structure (McGuire et al. 2014a).
Swimming and Diving Behavior
Belugas typically swim between 1 and 10 kilometer per hour (km/hr) (0.6–6.2 miles per hour [mi/hr]), but have been estimated to sustain speeds over 20 km/hr (12.4 mi/hr) for periods of a half hour (Richard et al. 1998). Suydam (2009) estimated typical speeds at 2.5–3.3 km/hr (1.5– 2.0 mi/hr), and Smith and Martin (1994) estimated swimming speeds of 1.6–6.0 km/hr (1.0–3.7 mi/hr) during the fall migration.
According to Goetz et al. (2012a), CI belugas tagged from 1999–2000 displayed a mean transit rate of 2.8 (SD ±2.4) km/hr (1.7 mi/hr), with individuals’ travel rates ranging from 1.6 (SD ± 2.0) km/hr to 4.3 (SD± 3.1) km /hr (1.0–2.7 mi/hr). Tagged CI belugas travelled faster during December to May than June to November, and travelled slower in coastal areas than they did in offshore waters of the Inlet (Goetz et al. 2012a). Based on an acoustic study conducted in Eagle River, swimming speeds of CI belugas were estimated to be from 1.8–7.56 km/hr (1.1–4.7 mi/hr) (Castellote et al. 2013).
Belugas from stocks found in regions with access to deep water are capable of dives deeper than 1,000 m (3,281 ft) (Citta et al. 2013) and at vertical speeds of 2–7 km/hr (1.2–4.3 mi/hr; Heide-Jørgensen et al. 1998). In the areas of Cook Inlet occupied by belugas, the depth does not exceed 100 m and much of the time the belugas are in waters less than 20 m (65.6 ft) depth. Consequently, CI belugas are able to access the entire water column. Typical dive sequences consist of three to five short intervals of 7–10 seconds followed by a longer dive of a minute or more. Mean dive depth ranged from 1.6 (SD ± 2.1) to 6.7 (SD ±10.4) m (5.2 to 22 ft) and mean dive duration ranged from 1.1 (SD ±1.3) to 6.9 (SD ±9.5) minutes (Goetz et al. 2012a), with shorter dives occurring in nearshore areas. The average dive interval (the time from the beginning of one surfacing to the beginning of the next) is 24.1 seconds for CI beluga (Lerczak et al. 2000).