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Declining Steelhead:Study Says Conditions Early In Marine Life Phase Strong Contributors To Survival
Posted on Friday, July 14, 2017 (PST)

West 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.

 

Although 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.

 

Steelhead 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.

 

“This 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 continued.

 

As 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.

 

“Therefore, 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.”

 

Other species of salmonid, including juveniles, are also being targeted by predators in Puget Sound, British Columbia and in the Columbia River.

 

The 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.

 

They 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.

 

"We 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 single study."

 

The information shows differences in populations originating from different areas, she added.

 

“In 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 Act.”

 

The 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.

 

Populations 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.

 

Similar trends were found for adult abundance. Adults in Puget Sound in the 2000s declined by 53 percent on average compared to the 1980s.

 

The 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.

 

Survival 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)

 

To 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.”

 

She 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.

 

The 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.

 

Also See:

 

-- 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

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