A newly published study finds that hatchery
supplementation after 22 years in two Idaho drainages, increased chinook salmon
abundance at some life stages, but the effects did not persist after
supplementation of hatchery stock ceased and had no apparent influence on
The study, according to its authors,
represents one of the largest manipulative experiments ever undertaken in the
fisheries field. It found that, while supplementation can be a useful tool, the
underlying causes of population declines need to be addressed.
It is a distillation of a previous report that
was reviewed in 2016 by the Independent Scientific Review Panel (see CBB,
August 12, 2016, “Science Review Of Idaho Salmon Supplementation Study
Discusses ‘Pivotal’ Questions,” http://www.cbbulletin.com/437298.aspx\).
In that review, the ISRP said that “The
questions addressed by the study are pivotal for salmonid restoration and
recovery. The study’s extensive geographic scope, use of treatment and
reference populations, long duration, comprehensive field data, and analytical
approaches have provided managers and policy makers with insights and
recommendations on how supplementation should occur and be evaluated throughout
The study of supplemented chinook salmon in
the Salmon and Clearwater sub-basins involved 27 streams. Some13 of the streams
were supplemented and 14 were reference streams.
The ISRP review, “Review of the Idaho
Supplementation Studies Project Completion Report 1991-2014,” can be found on
the Northwest Power and Conservation Council website at http://www.nwcouncil.org/media/7150431/isrp2016-9.pdf.
The study defines supplementation as “the use
of artificial propagation to maintain or increase natural abundance while
maintaining the long-term productivity of the target population.”
“Here we focus on the relevant results and
their implications, while sparing the reader most of the program’s background
information and history” of the previous report, said David Venditti, senior
fisheries research biologist with the Idaho Department of Fish and Game.
He said the evaluation is of the “demographic
effects of supplementation broadly at the basin level and more intensively
using just the subset of supplemented populations with weirs. Our intention is
that managers can use these results to estimate the benefits they could expect
from supplementation and to provide guidance on implementing future programs.”
Apart from the wide scope of the study, two
things set it apart from other supplementation studies, he said: it includes
multiple reference streams to help measure the treatment effects and
supplementation was actually stopped in order to assess the techniques’
“A few studies have done one or the other but
none, to the best of our knowledge, have done both,” he said. “And as such,
despite being over two decades old, the study design remains cutting edge.”
“Effects of hatchery supplementation on
abundance and productivity of natural-origin Chinook salmon: two decades of
evaluation and implications for conservation programs,” was published online
Dec. 4, 2017, in the Canadian Journal of Fisheries and Aquatic Sciences (http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2016-0344#.WlecN6inHIU).
Venditti’s co-authors are Ryan Kinzer,
research scientist with the Nez Perce Department of Fisheries Resource
Management; Kim Apperson, regional fisheries biologist, Matt Belnap, regional
fisheries manager, Matt Corsi, principal fisheries biologist, Bruce Barnett, data
coordinator, and Timothy Copeland, program coordinator, all with IDFG; and Kurt
Tardy, fisheries biologist with the Shoshone-Bannock Tribes Fisheries
Among the conclusions, according to Venditti,
-- Supplementation increased the abundance of
natural-origin parr and smolts to Lower Granite Dam, but had a smaller effect
on adult returns.
-- The overall effect was greater in the
Salmon basin, where supplementation stocks were integrated with the natural
population than in the Clearwater basin where they were not.
-- However, the supplementation effect did not
persist into the post-supplementation phase. After supplementation ceased,
abundance and productivity in supplemented and reference populations returned
to approximately their pre-supplementation relationships, suggesting that the
long-term effects of supplementation were neutral.
-- Abundance increases were most effectively
generated by increasing the number of natural origin females in the spawning
population, while integrated supplementation females were slightly better or
about the same as females from the segregated hatchery stock.
The study concluded that supplementation can
be useful for fisheries managers as a way to maintain natural populations, but
it is not a stand-alone recovery tool because it does not address the
underlying mechanisms responsible for population decline.
“Based on these findings, we provide guidance
for conservation programs,” the study says. “Supplementation alone is not a
panacea because it does not correct limiting factors, which must be addressed
to achieve population levels capable of sustaining ecological function and
Venditti said the authors’ intentions were for
fisheries managers to use the study results to estimate benefits they can
expect from a supplementation program.
For managing wild populations, the first
priority should be to increase natural-origin abundance through other means,
such as habitat restoration, he said. If supplementation is necessary, a brood
stock integrated with the natural population would be preferred, but if
sufficient wild fish are not available, localized or nearby hatchery stocks
could provide benefit if used judiciously.
Similarly, for supplementation stocks, he
continued, maintaining the link between the hatchery and natural populations
should be a priority.
Also, when natural origin escapement is
moderate to high, consider using supplementation fish to seed under-utilized or
newly restored habitat to bring new production areas online and reduce spawning
density in core habitats.
“The decision to supplement is at least
partially a policy decision based on perceived risks versus potential
benefits,” he said. “We identify several areas where supplementation programs
can be beneficial, so it should continue to be one part of the region’s
integrated management strategy.
The study shows that supplementation can lead
to a short-term stabilization or even a slight increase in abundance with
little or no reduction to productivity, he added.
“But managers need to realize that salmon
supplementation should be intended to get populations over the hump, while the
underlying mechanisms affecting the population are addressed. Our clearest,
positive effects were observed in the freshwater life stages, indicating that
the hatchery/supplementation fish reproduced successfully,” he said.
Species not affected by the out-of-basin
factors salmon encounter, such as sturgeon and burbot, could also benefit from
this type of intervention, Venditti added.