| Summary: | Beluga whales (Delphinapterus leucas) have a protracted nursing period estimated to last from 6–32 months, although current estimates of beluga nursing duration are derived using approaches subject to capture bias. Recent studies have shown stable isotope profiles of dentin growth layer groups (GLGs) in marine mammal teeth serve as a reliable nursing proxy and can be used to assess individual weaning patterns. We measured stable isotope ratios of nitrogen (δ15N) and carbon (δ13C) of dentin GLGs in teeth from eastern Canadian Arctic belugas to estimate weaning age and assess relative contributions of milk and solid food during the nursing period. δ15N declines of ∼1‰ over the first 3 GLGs of most individuals were interpreted as evidence of weaning. Individual δ15N profiles indicated 15 of 27 whales were completely weaned by the end of their 2nd year, although a number of whales were weaned by the end of their 1st or 3rd year (9 and 3, respectively). Intermediate GLG2 δ15N values relative to GLGs 1 and 3 indicated most whales consumed a mixture of milk and solid food during their 2nd year, consistent with gradual weaning. Contrary to predictions based on parental care theory, nursing duration was not related to relative GLG width (used as a proxy for somatic growth) and did not differ for females and males, or among populations. δ13C variation was not a reliable indicator of nursing duration, as approximately half of the whales showed no ontogenetic δ13C patterns across GLGs deposited over the nursing period. This study provides novel life history information, which may inform beluga conservation and management decisions, and indicates belugas share prolonged nursing duration marked by individual variation observed in other odontocetes.
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