Bomb radiocarbon dating calibrates beluga (Delphinapterus leucas) age estimates

Abstract

The ages of many mammals are estimated by counting growth layers in tooth sections, yet validation of age estimation techniques using free-ranging mammals has been problematic. Contrary to age estimates for most other animals in which it is assumed that one bipartite growth increment forms annually, beluga whale ( Delphinapterus leucas (Pallas, 1776)) age estimates have been calculated assuming that two growth layer groups (GLGs) form each year. Here we report the age validation for belugas based on date-specific incorporation of atomic bomb radiocarbon into tooth GLGs. Radiocarbon assays of dentinal layers formed in belugas harvested between 1895 and 2001 indicated that radiocarbon from atmospheric testing of nuclear weapons was incorporated into growing teeth and retained for the remaining life of the animal. Comparison of age determined by bomb radiocarbon with age determined by GLG counts indicated that GLGs form annually, not semiannually, and provide an accurate indicator of age for belugas up to at least 60 years old. Radiocarbon signatures of belugas were temporally and metabolically stable and were apparently derived more from the radiocarbon content of their prey than from water. Our understanding of many facets of beluga population dynamics is altered by the finding that this species lives twice as long as previously thought.

Morbidity and mortality in stranded Cook Inlet beluga whales Delphinapterus leucas

“…1) included date, location, sex, and age class. As often as possible, mandibles were collected, and these animals were aged by sectioning teeth and counting growth layer groups (GLGs) (Wainwright & Walker 1988, HeideJørgensen & Lockyer 2001, with age equivalent to 1 GLG yr −1 (Stewart et al 2006). Due to extreme tides and other environmental conditions, mandibles were not always collected, and some collected teeth were not sectioned.…”

Foraging ecology of ringed seals (Pusa hispida), beluga whales (Delphinapterus leucas) and narwhals (Monodon monoceros) in the Canadian High Arctic determined by stomach content and stable isotope analysis

“…The following tissues were collected from each animal less than four hours after harvesting and frozen ( (208C): whole stomach (ringed seals: n019, 2010; belugas: n012; narwhals: n 03), liver and muscle (ringed seals: n021, 2010, and n06, 2011; belugas: n012; narwhals: n03), a tooth from the 2nd and 5th position on the right mandible (belugas; following Stewart et al 2006), and lower and upper canines (ringed seals; following Stewart et al 1996). The frozen tissue samples were later shipped to the University of Manitoba and stored at (208C until analyses.…”

“…Beluga age was estimated by counting annual growth layers deposited in the dentine of mounted tooth sections (Stewart 2012). Belugas were classified as adult if they were ]12 years old (Stewart 1994;Stewart et al 2006). When teeth were unavailable, age (x, n02) and length (L, n01) were estimated as follows: L x ¼ 381:5e (male) (Luque & Ferguson 2010).…”

An Emerging Pattern of Declining Growth Rates in Belugas of the Beaufort Sea: 1989–2008

“…Total GLGs present in the dentine and cementum were read following sectioning, as previously described in Perrin and Myrick (1980). There continues to be disagreement in the literature about whether one or two GLGs are deposited annually (Brodie, 1982;Goren et al, 1987;Stewart et al, 2006;Brodie et al, 2013). Here we report "age" as equivalent to one GLG per year.…”