Age and Growth Analyses for the Endangered Belugas in Cook Inlet, Alaska

Daniel J. Vos, Kim E. W. Shelden, Nancy A. Friday, and Barbara A. Mahoney combined beluga age estimates from the teeth of hunted and stranded belugas during the period 1992–2001 with additional teeth collected up to June 2015. The earlier age estimates were determined by reading growth layer groups (GLGs) in the thin sections of teeth. The 2015 teeth results validated the number of GLGs deposited in the tooth dentine each year. The study compared ages obtained from each mandible and from the anterior to the posterior of the mandible to determine the “best” tooth for aging. The study then compared length-at-age models for Cook Inlet belugas.

Belugas (Delphinapterus leucas) are toothed whales of the Monodontidae family. This family includes only one other species, the narwhal (Monodon monoceros). Belugas are circumpolar in distribution and occur only in the Northern Hemisphere, in seasonally ice-covered seas of temperate, subarctic, and arctic regions. Belugas in U.S. waters surrounding Alaska are managed by the NOAA Fisheries as five discrete stocks designated by their summering areas (Muto et al., 2018). The Cook Inlet stock is genetically distinct (O'Corry-Crowe, Suydam, Rosenberg, Frost, & Dizon, 1997) and geographically isolated from the other stocks (Lowry, O'Corry-Crowe, & Goodman, 2012).

The geographic isolation of these whales, in combination with their site fidelity (Shelden et al., 2015), makes this stock vulnerable to hunting (Mahoney & Shelden, 2000) and other anthropogenic impacts (Norman et al., 2015). The Cook Inlet beluga population is listed as endangered under the U.S. Endangered Species Act. It is listed as critically endangered on the IUCN Red List (Lowry et al., 2012; NAMMCO, 2018). As the population continues to decline (Hobbs, Shelden, Rugh, Sims, & Waite, 2015a), the lack of basic life-history information has hampered attempts to determine causes (Hobbs, Wade, & Shelden, 2015b). In particular, knowing the ages of animals in this population is key to further demographic study.

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Vos, D. J. ; Shelden, K. E. W. ; Friday, N. A. ; Mahoney, B. A.; DOI, Marine Mammal Science