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

Dam trout: Genetic variability in Oncorhynchus mykiss above and below barriers in three Columbia River systems prior to restoring migrational access

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Experimental test of genetic rescue in isolated populations of brook trout

“…This provides support for the general importance of maintaining genetic diversity in small populations and adds to the growing understanding of the importance of genetic diversity in small salmonid populations. For example, a recent study of westslope cutthroat trout ( Oncorhynchus clarkii lewisi ) that translocated embryos from five sources were translocated into a vacant habitat found that the juveniles from the most genetically diverse source populations had higher survival (Andrews et al., ).…”

“…In addition to habitat size, the importance of connectivity for metapopulation persistence has been demonstrated for multiple salmonid species (e.g., Koizumi, ; Letcher et al., ). In response to anthropogenic barriers that disrupt metapopulation connectivity and reduce habitat size, translocations are becoming more widely considered in aquatic ecosystems (Andrews et al., ; Olden et al., ; Pavlova et al., ).…”

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