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Study Looks At Issues Regarding Sockeye Reintroduction Using Residualized Kokanee
Posted on Thursday, August 30, 2018 (PST)

When given the chance, landlocked sockeye – kokanee – will bolt for the ocean, but as it turns out in one study where a dam had been in place for 90 years, just 20 percent of kokanee in the reservoir were ready to smolt, according to a recent study out of Canada.


Sockeye populations that have been unable to migrate to salt water for decades due to dams and have residualized in the dam’s reservoir and are now managed as landlocked kokanee, apparently still retain the desire to smolt. However, there are genetic and environmental components to the salmon’s “decision” to smolt and whether a salmon has retained the ability to decide is largely unknown, according to one of the study’s authors.


“Sockeye salmon in Alouette Reservoir (British Columbia), where an impassable dam had blocked anadromy for nearly 90 years, started smolting when the opportunity arose, but the annual proportion of fish smolting is only about 20 percent of the population,” said author Brett van Poorten, senior aquatic scientist, with the British Columbia Ministry of Environmental and Climate Change Strategy. “This may be due to a loss of the smolting genotype from the population, high in-lake productivity (the reservoir is subject to a successful nutrient enhancement program) or other factors.”


The researchers, according to van Poorten, used a stock assessment model for Alouette sockeye to project population abundance of resident and anadromous sockeye in the future assuming uncertainty in heritability of smolting.


What they found was that the anadromous physical abilities declined over time due to low ocean survival and that supplementing anadromous sockeye through hatchery enhancement will increase anadromous runs, but still with very low return rates.


As the study says, “hatchery supplementation is unlikely to impact anadromous or resident sockeye significantly, although there is substantial prediction uncertainty suggested in projections. Our study suggests that providing passage for previous land-locked anadromous populations will lead to the return of anadromous fish in the short term, but long-term prospects are far from certain.”


“Overall, we suggest that providing passage for sockeye is unlikely to provide great returns in the future, though there is substantial uncertainty in our predictions,” van Poorten said. “However, a decision of this scale and importance involves evaluating multiple objectives; it may be that the poor ecological outcomes for sockeye are offset by ecological outcomes of all other Pacific salmon, as well as the substantial cultural value in providing ocean-run sockeye to the local Katzie First Nation.”


“Evaluating benefits of stocking on sockeye recovery projections in a nutrient-enhanced mixed life history population,” was published online in the Canadian Journal of Fisheries and Aquatic Sciences (


Van Poorten’s co-authors are Shannon Harris, limnology specialist, and Allison Hebert, research technician and currently a Master of Science student at the University of British Columbia.


Generally, anadromous sockeye salmon rear in fresh water for 1–3 years prior to smolting, migrate to the ocean, and remain there for 1–3 years before returning to fresh water to spawn and die, typically between age-3 and age-5, the study says.


Van Poorten said that he presumes that any place where salmon have residualized upstream of an impassible dam would have the same issues.


“Factors affecting year-to-year variability and long-term trends in smolting are generally poorly understood,” he said. “Investment in fish passage is a complicated decision involving many factors (expected biological outcomes, cost, cultural values); each of these factors rides on predictions of smolts once passage is re-established. Improving our ability to predict these outcomes (i.e. understand what leads to smolting) will help us make well-informed decisions.”


Among the study’s management implications, its predictions of anadromous and resident sockeye, if passage persists, helps inform expected recreational fishing outcomes (in terms of catch of resident sockeye) as well as possible conservation concerns of the anadromous fish, van Poorten said.


“More importantly, this work feeds into the long decision process addressing whether to install a permanent fish passage facility (e.g. a fish ladder),” he said.


Restoration of fish passage is often technically feasible but can often be expensive, and decisions on whether and where to invest in passage must appropriately weigh environmental, economic, social, and cultural values, the study says.


This study was possible because of the data collected over the past 20 years, including all the in-lake data on limnology and resident sockeye (by BC Ministry of Environment and Climate Change Strategy; funded by BC Hydro), smolt estimates (by Katzie First Nation and LGL Environment; funded by Fish and Wildlife Compensation Program) and return numbers (by the Alouette River Management Society and BC Corrections; also funded by Fish and Wildlife Compensation Program and BC Corrections).


“All these groups, together with Fisheries and Oceans Canada, meet regularly as part of the Alouette River Sockeye Reanadromization Project to provide information to inform the fish passage decision,” van Poorten said.


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