Isotopic and Elemental Studies: Forensic application of isotopic and elemental techniques to identify hatchery of origin of at-large trout.
Investigator: Brett Johnson
Introduction: Whirling disease presents a substantial threat to the viability of wild, naturally reproducing trout populations. Stocking of whirling diseased fish is thought to be an important factor in the spread of the disease to previously uninfected drainages. It has been virtually impossible to trace the origin of a fish once it has been stocked, but development of new technologies to accomplish this would present law enforcement personnel with an effective means of tracking sources of illicitly stocked trout and serve as a deterrent to future introductions.Objectives: We are examining the utility of otolith microchemistry analysis for identifying the geographic origin of trout. Otolith microchemistry is strongly related to water chemistry, which in turn is heavily influenced by geology. Trace elements in the ambient water such as Sr, Ba, Mg and Mn are deposited on the otolith in a concentration-dependent manner. In states like Colorado with diverse geologic formations, we predict that the differences in underlying geology would lead to large variations in water chemistry among bodies of water in the state. Our primary objective is to determine if multi-elemental “fingerprints” can be established for different geographic regions based upon differences in water chemistry.
Progress: Working relationships were established with managers at 17 CDOW hatcheries and they have been very cooperative, providing all the samples we need so far. We have analyzed water samples from hatcheries in Colorado and observed enormous variation among locations. We thus predict that analysis of otolith microchemistry will reveal significant differences among locations and relatively small variation within the fish collected at each site. If unique chemical signatures in otoliths exist and display a strong degree of similarity in fish reared in the same body of water, we believe that it will be possible to capture a fish at large and infer the area of origin.
Results/Products: A detailed report was provided to the funding agency and collaborators
in December 2004. Presentations summarizing
goals and methodology were given at the Whirling Disease
Symposium in February of 2005 and at the Colorado/Wyoming American
Society meeting in March of 2005.