The Use of Stable Oxygen Isotope (δ18O) Composition in Sockeye Salmon Body Fluid to Determine whether a Fish Has Been Caught in Freshwater

• Published in: North American journal of fisheries management 2009-06, Vol.29 (3), p.560-569
• Main Authors: Macdonald, R. W., Forsland, V., Withler, R. E., Patterson, D. A., Demsky, A.
• Format: Article
• Language: English
• ISSN: 0275-5947; 1548-8675
• DOI: 10.1577/M08-143.1

Fisheries enforcement is often tasked with determining whether a seized Pacific salmon Oncorhynchus spp. has been caught legally or illegally, either in freshwater while it was migrating to its natal stream or in the ocean at some point during its life cycle or migration. Here we show that the oxygen stable isotope composition (δ18O) of the water within seized fish tissue, together with DNA analysis, provides a powerful means of establishing where the fish was migrating and whether it was inhabiting freshwater when harvested. These tools are relatively easy to apply and are supported by an extensive set of microsatellite DNA data for sockeye salmon O. nerka that provide “forensic” identification and by a time series record for δ18O in the water of the Fraser River. The difference between δ18O composition in the river (∼−17‰) and the ocean (∼−2‰), together with conservative mixing between the end members, provides wide discriminatory power. Evaporation or sublimation during storage favors the light isotope and would thus be to the advantage of the defendant.