| Abstrakt: |
Many salmonids are listed as threatened or endangered under the U.S. Endangered Species Act (ESA), with habitat loss and alteration likely responsible for their declines. As a result, salmonid hatcheries have proliferated to help mitigate the loss of wild populations. Research aimed at understanding factors contributing to population declines, including studies designed to improve juvenile downstream passage, has often relied on hatchery-origin fish because of restricted access to wild fish. However, differences between hatchery-origin and wild fish could confound results. This led to the development of the Wild Fish Surrogate Program, where we use alternative rearing tactics to produce juvenile fish more like wild Chinook Salmon, Oncorhynchus tshawytscha, for research by varying growth, diet, feeding, density, cover, and tank complexity. Here, we describe methods that have been successful in producing target wild fish phenotypes, in particular related to smoltification and movement, and provide information on the quality and phenotypic accuracy of wild fish surrogates through four case studies (morphology, fin condition, body composition, and behavior). We show that wild fish surrogates had more similar body shape to wild fish compared to hatchery fish and had intermediate body lipid levels. Compared to hatchery fish, we also show that wild fish surrogates had larger and more symmetrical fins and were less likely to cross an aversive zone to be near conspecifics. Although wild fish surrogates were not always intermediate in their phenotypes or behavior, they did not significantly differ in their caudal fin length asymmetry or behavior compared to wild fish. We outline how such a program can be expanded beyond the program objectives and beyond salmonids. This generalization is important, as it can be implemented in other systems with ESA-listed populations where research using wild fish could inform and improve mitigation efforts or for hatchery programs to produce more wild-like phenotypes. [ABSTRACT FROM AUTHOR] |
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