Coast steelhead runs are declining and a new study pegs much of the problem to poor
survival of smolts early after entry into the ocean.
After entering the
ocean, steelhead smolts head out over the continental shelf from wherever they
enter the ocean – British Columbia, Puget Sound, the coastal areas of Oregon
and Washington and from the Columbia River – and then turn north to the Gulf of
Alaska where the fish all mix before returning to their natal spawning grounds.
While in the Gulf of Alaska steelhead remain more dispersed and school less
than salmon while in the ocean.
steelhead are known for this long-distance migration in the ocean, it appears
that conditions close to where young steelhead enter the ocean from freshwater
contributes more to their survival than conditions in the open ocean.
abundance in the Pacific Northwest has declined since the 1980s and marine
survival rates have likely contributed to that decline, especially for lower
Columbia River and Puget Sound steelhead.
“Our paper suggests that conditions early in
the marine life phase of steelhead trout, shortly after they enter salt water,
are strong contributors to their total marine survival patterns,” said Dr.
Neala Kendall, research scientist with the Washington Department of Fish and
Wildlife, and lead researcher of the study.
suggests that the steelhead are either compromised when they enter marine
waters, such as from contaminants or parasites, and/or that they are more
likely to be eaten by a predator in recent years than in the 1980s,” she
for predators – harbor seals, harbor porpoises, birds and fish-eating fish – it
could also be that there is less other food, such as the forage fish herring
and anchovies, in Puget Sound for these predators to eat, so they target
steelhead smolts more, Kendall said.
management actions that reduce contaminants and parasites and promote and
protect forage fishes, such as reducing shoreline armoring, could be helpful,”
she said. “We are currently in the process of conducting additional work that
will shed more light on what factors are related to this increased mortality.”
species of salmonid, including juveniles, are also being targeted by predators
in Puget Sound, British Columbia and in the Columbia River.
study’s researchers analyzed steelhead adult abundance from 35 coastal British
Columbia and Washington populations, along with smolt to adult return
information from 48 populations from Washington, Oregon and the Keogh River in
B.C. It found that more than 80 percent of the populations studied had declined
since the 1980s.
also found that smolt survival declines were seen in three of four populations
since the 1990s, including the Columbia River, Puget Sound and the Keogh River.
were able to compile data from multiple reports and databases to document
survival in the ocean of Oregon, Washington, and B.C. steelhead trout and show
that these trends paralleled declines in adult abundance and also differ among
populations originating from different areas," Kendall said. "We
believe this is the first time these data have been brought together in a
information shows differences in populations originating from different areas,
particular, Lower Columbia River and Puget Sound steelhead marine survival
rates have declined since the early 1980s. These declines likely contributed to
these fishes’ low abundance and listing on the Endangered Species Act. Coastal
Oregon and Washington steelhead marine survival rates have varied over time but
have not declined in the same way that Lower Columbia River and Puget Sound
steelhead have. Coastal steelhead are not listed on the Endangered Species
study, “Declining patterns of Pacific Northwest steelhead trout (Oncorhynchus
mykiss) adult abundance and smolt survival in the ocean,” was published online
June 26, 2017, in the Canadian Journal of Fisheries and Aquatic Sciences ” (http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2016-0486#.WWTmQIjyvIU). Kendall’s
co-authors are Gary Marston, natural resource scientist, and Matt Klungle,
research scientist, both with WDFW.
with particularly concerning declines were those in the Lower Columbia River
and in Puget Sound. Ocean survival of juvenile steelhead populations in Puget
Sound in the 2000s declined by 77 percent on average compared to the 1980s, the
study says. Survival averaged 3.1 percent in the 1980s but dropped to 0.7
percent in the 2000s.
trends were found for adult abundance. Adults in Puget Sound in the 2000s
declined by 53 percent on average compared to the 1980s.
declines in juvenile survival "likely contributed to these fishes' low
abundance," Kendall said. Abundances are so low that Puget Sound steelhead
were listed for protection under the ESA in 2007. Steelhead populations in B.C.
included in the study also have declined in abundance and ocean survival since
the 1980s. Declines in survival of juvenile steelhead in ocean environments
were not as drastic for populations along the coasts of Washington and Oregon
which are not listed under the ESA.
and abundance trends, like those generated in this study, can enhance current
tools being used to predict changes in steelhead populations, according to a
news release published in Phys.Org (https://phys.org/news/2017-06-steelhead-trout-population-declines-linked.html)
best conserve steelhead in the Northwest, Kendall said "stakeholders and
concerned citizens want to better understand why these populations have been
struggling and how marine survival has contributed. With this information,
policymakers and managers can have different expectations about Puget Sound and
Lower Columbia steelhead [compared to] fish on the coast due to their different
marine survival patterns.”
sees this study as providing further support for ongoing efforts by natural
resource agencies and NGOs to improve steelhead survival and protect the
habitats these juvenile trout use upon arriving in the ocean.
research is part of the Salish Sea Marine Survival Project, a US-Canada
collaboration of more than 60 organizations conducting research to understand
why salmon and steelhead are dying in the Salish Sea.
CBB, July 7, 2017, “Study: Harbor Seals Target Salmon Juveniles Of Conservation
Concern In Salish Sea,” http://www.cbbulletin.com/439218.aspx
CBB, June 23, 2017, “Puget Sound Study: Pinniped Predation On Juvenile Salmon
Making Salmon Recovery More Difficult,” http://www.cbbulletin.com/439144.aspx
CBB, June 23, 2017, “Pinniped Report: Sea Lions Leave Bonneville Dam With
Likely High Salmon Predation Rate In Their Wake,” http://www.cbbulletin.com/439149.aspx