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Study: Less Healthy Adult Sockeye Migrate Earlier Than Healthy Fish To Freshwater
Posted on Friday, June 08, 2018 (PST)

Sockeye salmon showing signs of disease and stress are motivated by their condition to leave salt water and enter fresh water earlier than healthier salmon, according to a recent study.


Yet, as disease and stress progress after entering warmer freshwater, the early returning and less healthy fish may not survive that new environment as well as the healthier fish, the study says.


“We proposed that immune compromised fish were more motivated to migrate into freshwater, and thus, experienced higher survival due to a reduced chance of encountering Pinniped predators in the ocean,” said S. Matthew Drenner, fish biologist, Department of Forest and Conservation Sciences, University of British Columbia. “However, once in freshwater, these fish could experience reduced survival due to progression of a disease state when they encounter warmer waters in river.”


The findings likely would be similar in the Columbia River basin for diseased or stressed fish that also enter a warm freshwater environment.


“More broadly speaking, we are really at the forefront of understanding the role pathogens (i.e., disease causing agents) play in influencing salmonid behavior and survival across all phases of the salmonid life-cycle,” Drenner said. “Sockeye from other systems, such as the Columbia River basin, and other salmonid species contend with similar issues (e.g., disease and stress) during migrations. After all, pathogen presence and stress are an inherent part of life for all animals.


“Disease progression can be exacerbated when fish encounter additional stressors such as high water temperatures and fisheries, both of which are present in the Columbia River basin,” he said.


“Transcriptome patterns and blood physiology associated with homing success of sockeye salmon during their final stage of marine migration” was published online in December in the Canadian Journal of Fisheries and Aquatic Sciences (


Drenner’s co-authors are Scott G. Hinch, professor, Nathan B. Furey, fish ecologist, and Timothy D. Clark, associate professor, all with the Department of Forest and Conservation Sciences, UBC; Shaorong Li and Tobi Ming, Kristina M. Miller, all molecular biologists, and Ken M. Jeffries, assistant professor, all with Fisheries and Oceans Canada, Pacific Biological Station; David A. Patterson, fisheries biologist, Fisheries and Oceans Canada, Science Branch, Pacific Region, Cooperative Resource Management Institute, School of Resource and Environmental Management, Simon Fraser University; Steven J. Cooke, professor, Fish Ecology and Conservation Physiology Laboratory, Institute of Environmental Science and Department of Biology; David Robichaud, fisheries biologist, LGI Limited; David W. Welch, fisheries biologist, Kintama Research Services Ltd; Anthony P. Farrell, professor, Department of Zoology and Faculty of Land and Food Systems, UBC; and Kristina M. Miller, molecular biologist,


The researchers captured 313 adult sockeye in the marine environment by either troll or seine, took blood samples and measured the fish, then released them immediately. Some had a tissue biopsy, others didn’t. Those without the biopsy were returned to the water in less than three minutes, the others in less than five minutes. Individual fish were detected at fixed acoustic telemetry arrays along the migration route.


Some 71 to 80 percent of the fish made it to the first detection point (the other side of the coin is that 20 to 29 percent of the fish died prior to reaching the first detection point) and 53 to 66 percent made it to the lower Fraser River (34 to 47 percent died or disappeared).


“Moreover, gene expression differed substantially between those fish that showed the best survival (96 percent) and those that showed 68 percent survival. Marine survival was specifically related to multiple physiological processes identified from gene expression and blood physiology including stress, immune response, metabolic processes, and osmoregulation,” the study says.


The researchers said their primary objective in the study was to test “whether gene expression could predict marine survival. Both microarray and biomarker data indicated marine survival was related to multiple biological processes, including responses to infection, stress, protein biosynthesis, metabolism, and osmoregulation.”


Although faster migration of these compromised fish seems counterintuitive, the study says, “it is possible that signals associated with enhanced stress and immunity may accelerate their drive to move towards spawning grounds before they die.”


Overall, this study supports the idea that infection and stress are important biological processes influencing behavior and fate of sockeye salmon during homing migrations, the study concludes.


Drenner said management implication are varied: “if diseased fish enter the river earlier and have lower in-river survival than healthy fish (as shown in Miller et al. 2011), these fish could perhaps be targeted by in-river fisheries since they may not contribute to reproduction.”


However, counter to that, “fisheries could attempt to avoid diseased fish in order to reduce encounters with in-river stressors in the hope of increasing survival of these fish.”


A next step is identifying specific pathogens responsible for disease in migrating fish, Drenner said.

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