Title
Telemetry validated nitrogen stable isotope clocks identify ocean-to-estuarine habitat shifts in mobile organisms
Author(s)
Shipley, Oliver N.;Newton, Alisa H.;Frisk, Michael G.;Henkes, Gregory A.;LaBelle, Jake;Camhi, Merry;Hyatt, Michael;Walters, Hans;Olin, Jill A.
Published
2021
Publisher
Methods in Ecology and Evolution
Abstract
1.Throughout their life history, many animals transition among heterogenous environments to facilitate behaviors such as reproduction, foraging, and predator avoidance. The dynamic environmental and biological conditions experienced by mobile species are integrated in the chemical composition of their tissues, providing retrospective insight into movement.
2. Here, we present a unique nitrogen stable isotope clocks (‘isotopic clocks’), which integrate tissue turnover rates, consumer stable isotope ratios, and habitat‐specific isotope baselines and can be used to predict time‐since‐immigration and the timing of habitat shifts in migratory animals. Isotope values of blood plasma to derive time‐since‐immigration estimates and timing of seasonal habitat shifts for juvenile sand tiger sharks (Carcharias taurus); a species known to perform seasonal movements between ocean and estuarine environments.
3. Isotopic clocks estimated for 65 individuals sampled across six years illustrated that juvenile sand tiger sharks predominantly arrived at estuarine habitats between June and July, with some individuals arriving as early as mid‐May. Our modeling approach was validated by comparing isotope‐derived estuarine arrival times with those from acoustically tracked individuals. The median day of entry for each sampling population were within the range of entry times estimated from acoustic telemetry.
4. Sensitivity analyses indicated isotopically inferred time‐since‐immigration and estuarine arrival estimates were robust to variation in isotopic turnover rate and diet tissue discrimination factors under multiple modelling scenarios. This suggests that parameterization of the isotopic clock provides reliable estimates of time‐since‐immigration and day of arrival into new habitats if isotopic variation is existing between origin and new locations.
5. Our study presents a unique application of telemetry‐validated isotope clocks to derive retrospective estimates of time‐since‐immigration and timing of habitat shifts for animals that seasonally traverse heterogeneous environments. This approach can be readily applied across many temporal and spatial scales, and to other species and ecosystems to facilitate rapid assessment of changes in animal habitat use and broader ecosystem structure.
Keywords
Carcharias taurus;ecosystem connectivity;habitat use;heterogenous habitats;movement ecology;shark
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PUB25609