Who's Your Momma? Recognizing Maternal Origin of Juvenile Steelhead Using Injections of Strontium Chloride to Create Transgenerational Marks

Abstract

We sought to determine whether a strontium chloride injection could be used to create a transgenerational otolith mark in steelhead Oncorhynchus mykiss. Two strontium injection trials and a survey of strontium: calcium (Sr:Ca) ratios in juvenile steelhead from various steelhead hatcheries were conducted to test the feasibility of the technique. In both trials, progeny of fish injected with strontium had significantly higher Sr:Ca ratios in the primordial region of their otoliths, as measured by an electron wavelength dispersive microprobe. In trial 1, the 5,000-mg/L treatment level showed that 56.8% of the otoliths were correctly classified, 12.2% being misclassified as belonging to the 0-mg/L treatment. In trial 2, the 20,000-mg/L treatment level showed that 30.8% of the otoliths were correctly classified, 13.5% being misclassified as belonging to the 0-mg/L treatment. There were no differences in the fertilization rates of eggs or survival rates of fry between the treatment and control groups. The Sr:Ca ratios in otoliths collected from various hatchery populations of steelhead varied and were greater than those found in otoliths from control fish in both of our injection trials. This study suggests that the marking technique led to recognizable increases in Sr:Ca ratios in some otoliths collected from fry produced by injected females. Not all progeny showed such increases, however, suggesting that the method holds promise but requires further refinement to reduce variation. Overall, there was a correct classification of about 40% across all treatments and trials; the variation in Sr:Ca ratios found among experimental trials and hatcheries indicates that care must be taken if the technique is employed where fish from more than one hatchery could be involved.

Received January 23, 2009; accepted March 23, 2011

ACKNOWLEDGMENTS

The authors would like to extend their gratitude to the editor and anonymous reviewers for their comments and suggestions for improving this manuscript. Funding for this research was provided by Bonneville Power Administration (project 2002-030-00). We thank the Oregon Department of Fish and Wildlife, and Idaho Fish and Game for providing fish used in this study. We are grateful to the following individuals for their assistance during this study: P. Lofy, C. Zimmerman, J. Seigle, L. Naylor, and S. Archer. A special thanks to Frank J. Tepley III, and Roger Nielsen for access to Oregon State University electron microprobe laboratory and providing analytical support. Reference to trade names does not imply endorsement by the U.S. Government.

Notes

^aData from control groups from trials 1 and 2.

^bWinter-run steelhead; the remainder of the samples came from summer-run steelhead.