Performance of Juvenile Cutthroat Trout Translocated as Embryos from Five Populations into a Common Habitat

Abstract

The distributions of most native trout species in western North America have been severely reduced, and conservation of many of these species will require translocation into vacant habitats following removal of nonnative species. A critical question managers have is “Does it matter which donor sources are used for these translocations?” We present a case study that addressed this question for a large native trout translocation project in Montana. We introduced embryos from five source populations of Westslope Cutthroat Trout Oncorhynchus clarkii lewisi to a large, fishless watershed in Montana following removal of nonnative fish with piscicides. Source populations providing embryos for translocations were three nearby (<120 km) wild populations, the state of Montana’s captive Westslope Cutthroat Trout hatchery conservation population (initiated 32 years ago using fish from wild populations located >350 km from the translocation site), and a population in captivity for one generation comprised of individuals from the three wild populations used as single sources for this project, which were variably crossed (59% within populations and 41% between populations) to provide embryos. We used remote-site incubators at six different sites to introduce approximately 35,000 embryos from 400 genotyped parents. We later resampled and genotyped 1,450 of these individuals at age 1 and age 2. Juvenile survival for the more genetically diverse Montana Westslope Cutthroat Trout conservation population was twice as high as for other source populations, even though these other source populations were geographically closer to the translocation site than populations used to make the Montana Westslope Cutthroat Trout conservation population. Body weight for progeny from the two captive populations was higher than for progeny from wild source populations, and some differences were observed in body condition among source populations. Continued monitoring over several generations will be necessary to determine the eventual contributions of each source population and the relevance of these initial findings.

Received October 9, 2015; accepted February 27, 2016 Published online July 20, 2016

ACKNOWLEDGMENTS

Funding was provided by Turner Enterprises, Inc., Montana Trout Unlimited, and the National Science Foundation (DEB 0717456). We thank Dan Drinan, Travis Lohrenz, Romie Bahram, Jake Ferguson, Jacqueline Jones, Jennifer Ard, Alex Hopkins, Clint Smith, Tatiana Butler, Ninh Vu, Wes Orr, Buddy Drake, Angela Smith, Mark Sweeney, Reid Koskiniemi, Mike Konsmo, Hillary Billman, and Preston Debele for their assistance in the field. We also thank Ninh Vu, Jenn Ard, and Tatiana Butler for their assistance in the lab. We thank two anonymous reviewers and an associate editor for constructive and valuable feedback on an initial draft of this manuscript. The Montana Cooperative Fishery Research Unit is jointly sponsored by the U.S. Geological Survey, Montana Fish, Wildlife and Parks, Montana State University, and the U.S. Fish and Wildlife Service. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This study was performed under the auspices of Montana State University Institutional Animal Care and Use protocol 18-07.