Individual variation in nursing duration and resource use among narwhals (Monodon monoceros) from eastern Canadian Arctic using stable isotopes (d13C and d15N) of dentine from embedded teeth
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Date
2020-08-17
Authors
Zhao, Shu-Ting
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Abstract
Individual variation in nursing duration and resource use can have cumulative effects on population growth and species resilience in response to resource changes. There have been climate-induced shifts in prey resources in the Arctic since the 1980s; however, knowledge regarding narwhal nursing and dietary variation at the individual level remain understudied. Stable isotope analysis (SIA) of sequential dentine samples can provide a longitudinal record of isotopic (13C and 15N) values that help infer age at which nursing completes, and assess diet. This study used SIA of dentine from narwhal embedded teeth to investigate individual nursing duration and dietary variation within a population over two time periods (pre- and post- 1982/1983). Embedded teeth were collected near Pond Inlet, Nunavut, from both sexes in 1982/1983 (n = 13) and 2015/2017 (n = 14). Ontogenetic 13C and 15N profiles were constructed for individual narwhals. Nursing duration was inferred based on postnatal 15N decline over age 1–10, and I found nursing in narwhals lasted for two to six years but most individuals started feeding primarily on solid food after 12 months. Nursing duration did not differ between sexes nor between the two time periods. To analyze variation in narwhal diet after nursing being completed, I evaluated 13C and 15N values and isotopic niche breadth for individuals within each period and at the population level between the two time periods. Narwhals varied significantly in their isotope values and isotopic niche, suggesting individuals may differ in resource use (prey size, proportion, and feeding locations), as well as the range and consistency of resource use over one’s lifetime. Across time periods, narwhals showed a slight niche expansion, likely reflecting a dietary shift to incorporate alternative subarctic prey that have increased in availability in the Arctic over the past 30 years. This study provides new information on narwhal life history, highlighting the variability in narwhal nursing duration and individual-level resource use, which can be applied to future assessments that consider narwhal foraging flexibility in response to climate-induced resource shifts.
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Keywords
Narwhals, nursing, diet, stable isotopes, dentine