Stable isotope-based location in a shelf sea setting:: accuracy and precision are comparable to light-based location methods

Abstract

Summary
1. Retrospective determination of location for marine animals would facilitate investigations of migration, connectivity and food provenance. Predictable spatial variations in carbon and nitrogen isotopes in primary production across shelf seas provide a basis for stable isotope-based location.
2. Here, we assess the accuracy and precision that can be obtained through dietary-isotope-based location methods. We build isoscapes from jellyfish tissues and use these to assign scallops of fixed and known individual location, and herring with well-understood population-level distributions in the North Sea.
3. Accuracy and precision for retrospective isotope-based location in the North Sea were of a similar order to light-based location devices, with 75% of individual scallops assigned correctly to areas representing c. 30% of the North Sea, with a mean linear error on the order of 102 km. Applying assignment methods to an alternative migratory species (herring) resulted in ecologically realistic assignments consistent with fisheries survey data.
4. Location methods based on dietary isotopes such as carbon and nitrogen recover the spatial origin of nutrients assimilated into tissues, and this may not correspond directly to the physical location if either the test animal or its prey is highly migratory. Stable isotope-based location can be applied to any marine-feeding organism or derived food product, but the ecological meaning of any assigned area will be more difficult to interpret for large, high trophic level, migratory animals with relatively slow isotopic assimilation rates.

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ORCID for Clive N. Trueman: orcid.org/0000-0002-4995-736X

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