Discriminating Canadian Arctic beluga management stocks using dentine oxygen and carbon isotopes

Abstract

ABSTRACT: In the eastern Canadian Arctic, belugas Delphinapterus leucas exhibit genetic and ecological differentiation across their distribution that forms the basis of management stocks for traditional Inuit hunts. Using oxygen and stable carbon isotope ratios in dentine phosphate (δ¹⁸O_P) and structural carbonate (δ¹³C_SC), respectively, we evaluated the spatial structure of 3 of these beluga stocks: Western Hudson Bay (WHB, n = 30), Cumberland Sound (CS, n = 44), and Eastern High Arctic-Baffin Bay (EHA-BB, n = 29). Pairwise comparisons revealed significant differences in δ¹⁸O_P and Suess-adjusted δ¹³C_SC among all stocks, with the exception of similar δ¹⁸O_P between the WHB and CS stocks. A linear discriminant analysis (LDA) model fit to 60% of the data set (training data) successfully classified 84% of the remaining belugas (test data) to their respective stocks based on hunt location. Isotopic overlap among stocks could reflect (1) homogeneous baseline stable isotope (SI) composition between geographically adjacent stocks, (2) some degree of marginal geographic overlap in ranges or individual movements among stocks, perhaps during late spring, or (3) confounding dietary influences that increased within-stock SI variation. Some misclassifications consistent with individual movements among stocks were supported by limited genetic data, with a small number of belugas hunted from the CS stock exhibiting both isotopic and genetic similarity to WHB belugas. Geographic stock differentiation inferred from oxygen and carbon isotope proxies largely corroborates current eastern Canadian Arctic beluga stock definitions, which is relevant not only for management purposes but also for monitoring changing beluga distributions in response to ongoing climate-driven changes in Arctic marine ecosystems.