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Fish School, Part 5: Experts Debate Impact of
Ocean Conditions on Salmon, Steelhead Survival

Analysis by Eric Barker
Lewiston Tribune, February 21, 2020

Some have postulated that the depressed state of Snake River salmon and steelhead
can be traced almost entirely to ocean conditions.

Survey of Science Literature: Delayed Mortality Estimates. Many variables influence the survival of Snake River salmon and steelhead, but perhaps none more than the hospitality of the Pacific Ocean in any given year.

Juvenile salmon and steelhead that survive their downstream migration through the Snake and Columbia river hydrosystem must next survive from one to three years in the ocean, and the first few weeks to months is critical. When ocean conditions are good, the young fish find abundant food and grow more quickly, making them stronger and boosting their chances of survival. When conditions are poor, food is scarce and predators associated with warmer water can be abundant. This diminishes their chances of survival.

Some have postulated that the depressed state of Snake River salmon and steelhead can be traced almost entirely to ocean conditions. Under this view, the effect of the ocean is so powerful that it swamps all other factors. To support this theory, its proponents point to other river systems with fewer or no dams that have also seen salmon declines in recent years.

Others say it is impossible to separate ocean and freshwater conditions when measuring overall survival. This group doesn't dispute that ocean conditions play a large role in salmon survival, but they say freshwater factors are also important. Many of them say that mortality related to dam and reservoir passage is present and significant in years with both good and poor ocean conditions.

They also point out the humans have no control over the ocean, but they can influence freshwater conditions through a series of actions up to and including breaching of the four lower Snake River dams. Because of this, they say, actions that reduce freshwater mortality in general and hydrosystem related direct and delayed mortality in particular are the best way to improve salmon and steelhead runs. They also note that climate change is projected to produce poor ocean conditions more frequently than in the past, making it even more important to take measures that reduce mortality in fresh water.

Ocean and salmon and steelhead

"When we get really big runs and really small returns, it's usually the ocean," said Laurie Weitkamp, a research fisheries biologist for National Oceanic and Atmospheric Administration fisheries at Newport, Ore. "We estimate on average about 95 percent of salmon that go to the ocean don't come back, so there is a lot of wiggle room. If it's a little bit higher or a little bit lower, it makes a huge difference."

The past five years or so have seen poor ocean conditions. It started with the formation of the so called "blob," a mass of warm water in the North Pacific. Just as it looked as though ocean conditions were returning to a more normal phase, with cooler water and nutrient-rich springtime upwelling, another heat wave developed. Scientists feared another blob, but those conditions have since deteriorated.

Nonetheless, Weitkamp said warmer oceans are likely to persist as a result of climate change.

"The amount of heat the oceans have absorbed, the energy contained within that is gigantic. We will probably have local areas that are cooler, but I think the heat is pretty much here to stay."

Nate Mantua, a NOAA scientist at Santa Cruz, and Lisa Crozier at the agency's Northwest Fisheries Science Center in Seattle agree oceans are likely to be warmer in the future. They both noted there are likely to be some small areas where warming is not has pronounced because of local wind and weather patterns.

"We expect temperatures to increase globally, and we know oceans are absorbing most of the excess heat from this increased greenhouse warming -- most of it being 90 percent," Mantua said.

He said the northern Pacific is also prone to increased acidification as seawater absorbs more carbon. Crozier noted that the northern Pacific hasn't warmed as quickly as global averages, and that could continue, but she still expects salmon and steelhead from the Columbia and other Northwest rivers will face increased temperatures in the future.

"I would say there is uncertainty in those kind of processes, the decadal timing, but given global ocean (temperatures are) warming at all depths, even the upwelled water will be warmer in the future."

Those dire predictions mean freshwater habitat is even more important, Weitkamp said.

"We can't control the ocean, but we can control human behavior and we can control freshwater. Now is when we need to double down to make sure we do everything we can to control freshwater habitat so fish that do go out in the ocean are in good condition."

She said increasing life history diversity of the fish will be important. Mantua said the same thing. Over the years, human development and actions such as producing massive numbers of hatchery salmon and steelhead and negatively altering habitat have decreased diversity. Essentially many of the fish bound for the ocean are cookie-cutter specimens in terms of their behavior, which diminishes diverse traits that may help fish survive in changing ocean conditions.

For example, he said hatchery fish are increasingly produced from fewer and fewer parents. They tend to be released at the same size and the same time. In the Snake and Columbia rivers, many of those fish are placed on barges and taken downriver to avoid harm via dam passage.

"I think one of the ways you might make life better for salmon in the future is just give them a lot more options on the freshwater side and make those habitats more productive and diverse so that they are hedging their bets in ways that should help reduce the control the ocean has on their total population."

Although Weitkamp said humans should do more to improve freshwater survival, she hedged when asked if that means taking steps to reduce what other researchers have identified as delayed mortality related to dams on the Snake and Columbia rivers. She noted the Fraser River in British Columbia has seen significant declines in salmon and steelhead life cycle survival in recent years.

"They are having the exact same problem, and they don't have any mainstem dams," she said.

But others disagree and say if reducing freshwater sources of mortality is key, then the hydrosystem on the Snake and Columbia rivers is one of the biggest opportunities to do so.

Howard Schaller, a retired fisheries research biologist who worked for the U.S. Fish and Wildlife Service, said many people have speculated delayed mortality related to dam passage would vanish or be significantly reduced in periods of good ocean conditions but the evidence says otherwise.

He and now retired Idaho Fish and Game fisheries biologist Charlie Petrosky have produced several papers on delayed mortality and shown it to be present and significant in years with both good and poor ocean conditions.

"What we saw was the overall life cycle survival rates remained depressed when Snake River salmon experienced cooler conditions in the late 1990s and early 2000s. So that notion they would disappear wasn't consistent with the data, and delayed hydrosystem mortality was still present."

He said in most years with good oceans, smolt-to-adult survival rates remained below the target of 2 percent to 6 percent, with a 4 percent average, and that those rates for runs that return to Columbia River tributaries such as the John Day River in Oregon, which is above three instead of eight dams, mostly hit those targets.

In fact, he noted that the decline of Snake River salmon and steelhead began in the 1970s after Snake River dams were constructed. That decline happened at a time when ocean conditions were good.

"Not only did we see delayed mortality persist through cool ocean conditions in the late 1990s and early 2000s, the decline began in the 1970s when there was still cool ocean conditions," he said. "The empirical evidence isn't really convincing that once we return to cool ocean conditions that delayed mortality is going to disappear."

In addition, he said fisheries managers and others should look to take actions that will benefit the fish in both good and poor ocean conditions, especially in light of the predictions that ocean conditions will be warmer -- poorer -- more frequently as a result of climate change.

"What in-river management actions can you implement under variable ocean conditions, because we don't really have any dials to change what ocean conditions are going to look like," he said.

Those in-river dials are increasing spill at the dams to speed water and fish travel time so they reach the ocean and estuary on the schedule the fish have developed through evolution and to reduce the number of times fish go through turbines or fish bypass systems, which are linked to higher rates of delayed mortality.

"The other option is breaching the four lower Snake River dams, which would provide that benefit for Snake River stocks and would yield conditions that would probably best approximate returning to smolt-to-adult return levels of an average of about 4 percent."

Related Links:
Fish School, Part 4: Death Delayed by Eric Barker, Lewiston Tribune, 2/7/20
Fish School, Part 3 by Eric Barker, Lewiston Tribune, 1/31/20
Fish School, Part 2: by Eric Barker, Lewiston Tribune, 1/24/20
Fish School, Part 1 by Eric Barker, Lewiston Tribune, 1/17/20

Analysis by Eric Barker
Fish School, Part 5: Experts Debate Impact of Ocean Conditions on Salmon, Steelhead Survival
Lewiston Tribune, February 21, 2020

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