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Study Looks At Ecological, Behavioral Factors Prompting Wild Salmon To Stray From Natal Areas
Posted on Friday, May 11, 2012 (PST)

The straying of wild salmon from their specific natal water can be a good thing in many cases, according to a research paper produced by University of Idaho scientists and published recently in the April edition of the Ecological Society of America’s journal, Ecology.


“Juvenile dispersal affects straying behaviors of adults in a migratory population” is authored by Ellen J. Hamann and Brian Kennedy of the departments of Fish and Wildlife Sciences and Biological Sciences at the University of Idaho in Moscow.


The fish can fill biological gaps that help their species maintain genetic diversity and survive, the study says. Genetic, life cycle diversity buffers a species across ages and against ecological changes that occur.


Straying generally has a negative connotation, hatchery fish wandering into places not of their origin and polluting the native, wild stock and reducing their natural ability to survive and thrive. Most straying studies have concentrated on hatchery stocks because of the ability to identify them and their origins. The UI study uses analysis of otoliths – tree ring-like calcium accumulations in fish that collect a running history of the fishes’ comings and goings.


The article can be found at:


The researchers studied a salmon population in Big Creek, a tributary of the Middle Fork Salmon River in central Idaho. Spawning habitat is characteristically patchy and adult salmon returning to Big Creek tend to aggregate in six distinct spawning clusters. The areas are located almost entirely in designated wilderness area. The basin encompasses some of the most pristine aquatic habitat in the contiguous United States, and each spring and summer, threatened chinook salmon return after navigating more than 1,000 river kilometers to access natal rearing sites.


“Considering that major alterations have occurred along the mainstem migratory corridor, the life history diversity related to juvenile and adult migration behaviors expressed in these remnant populations has likely contributed to species perseverance despite, at times, drastic declines from historical abundance,” the article says


According to the researchers the study is the first spatially explicit treatment of straying in a wild salmon population that links the propensity of straying from natal areas to individually based factors. The researchers used genetic analysis of isotopes in those otoliths to find higher straying in male fish, particularly if they were prone to disperse as juveniles.


“It has important implications for our understanding of colonization or range expansion dynamics, such as in the case of the major dam removal projects occurring in North America for which scientists would like to have a better idea of salmon straying rates to estimate colonization timing,” the paper says.


Following is the abstract for the article:


“The resilience of organisms to large-scale environmental and climatic change depends, in part, upon the ability to colonize and occupy new habitats. While previous efforts to describe homing, or natal site fidelity, of migratory organisms have been hindered by the confounding effects of fragmented landscapes and management practices, realistic conservation efforts must include considerations of the behavioral diversity represented by animal movements and dispersal.


The study uses “natural isotopic signatures (87Sr/86Sr) to reconstruct the migratory behaviors of unhandled individuals over their entire life cycle. We identify ecological and behavioral factors influencing the propensity to stray.”


The paper says that such things as food availability during adolescence, sex and other factors may affect where, within that basin, a fish decides to spawn.


“While knowledge of the spatial scale at which migratory fish populations home accurately is limited and unresolved (Quinn 2005, Quinn et al. 2006), our findings offer definitive support for the ability of wild chinook salmon to distinguish natal sites with high spatial precision while providing clearer definition to the scale at which straying occurs,” the paper says.


“Fine-scale straying was common in Big Creek, occurring with relatively high frequency between the adjacent spawning clusters in the upper basin. Further, the existence of straying varied between the two sites in the upper basin where carcasses were collected, with more fine-scale straying occurring from upstream origins to downstream spawning than the reverse pattern.


“At river reaches of increasingly fine scale, it is likely that final spawning decisions may be determined by local-scale site factors rather than precise homing ability, and it remains possible that salmon in this study accurately recognized natal scents but chose alternative sites in the nearby cluster based on physical habitat attributes conducive to reproductive success,” the study says.


“These findings lend support for the conservation of behavioral diversity for population persistence, and we propose straying as a mechanism for maintaining genetic diversity at low population densities,” according to the article’s abstract.

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