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
“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
“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 (http://www.nrcresearchpress.com/doi/10.1139/cjfas-2017-0438#.W4gc6uhKjIU).
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
“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.