The numbers of young salmon caught off the Oregon and Washington state coasts during an annual federal survey cruise this June were among the lowest recorded in the past 20 years.
In fact, numbers were low across nearly all the species researchers regularly catch or observe — from birds like the common murre to forage fish like anchovies and smelt.
Months ahead of schedule, as a kind of heads up, West Coast researchers, project managers and program directors decided to send out a memo in mid-August detailing their initial findings — data that would usually be combined with other information and put out on a webpage at the end of the year.
The data is preliminary, but researchers say it is clear many young coho and Chinook salmon didn’t survive the migration from freshwater streams and rivers to the ocean this year, while poor ocean conditions could impact salmon returns to the Columbia River for the next few years.
Brian Burke, of the National Oceanic and Atmospheric Administration’s estuarine and ocean ecology program and one of the authors of the memo, says the numbers need to be taken with a grain of salt. One research boat at one point in time can’t cover all the habitat, nor can researchers know for certain that where they drop a net is where the fish are present. But, he said, “it was clear that there were not many fish out there.”
As they continue to process additional data — salmons’ blood samples, growth hormone levels and stomach contents — Burke said their understanding of why so many juveniles apparently died could shift.
“I think the big picture is sort of settled,” he said. “It’s refining the ‘why’ rather than the ‘what.’”
It’s possible that with a scarcity of usual prey like anchovies, smelt and herring, “predators may have been forced to feed at higher rates on salmon,” the memo states. The memo also notes anomalies throughout the area surveyed: the biomass of northern copepods — salmon growth and survival is related to the abundance of these small crustaceans — has been low since 2014; the lowest levels of chlorophyll (a proxy for phytoplankton); changes in the jellyfish population.
Michael Tehan, assistant regional administrator for NOAA’s Interior Columbia Basin Office and the recipient of the memo, said the heads up provides him and the agency’s policymakers, fishery managers and those involved in habitat restoration work across the basin with “situational awareness.”
“Many studies have focused on the (salmon’s) freshwater phase, and there has been substantially less research on salmon during ocean residence,” said David Huff, estuarine and ocean ecology program manager with NOAA and another author of the memo. But, he added, the success of practices in freshwater that touch on the size, timing and abundance of migrating salmon depends on the ocean environment.
For those involved in restoration work — or the entities that fund this work — the memo is a reminder of the complexity of a salmon’s life cycle.
“People expect there to be noticeable, sometimes dramatic responses when they do conservation activities,” Tehan said. But the salmon are “a product of what happened when they migrated out to the ocean” — and what kind of ocean they entered.
Without the ability to distinguish between the different ways ocean, freshwater or estuary conditions impact salmon, it’s hard to say where conservation or recovery efforts are succeeding or failing, he clarified. “Large salmon returns may be mistakenly presumed to be a result of successful freshwater mitigation practices when they are in fact a function of favorable ocean conditions.”
“Similarly,” he added, “the effects of successful freshwater recovery actions may be masked or overridden by poor ocean conditions, leading to unwarranted changes to recovery actions.”
Between persistent, unusually warm surface temperatures and a strong El Nino event, the ocean hasn’t been normal for the last three years.
“When you look at the whole time series, the last three years really stand out as being something different,” said Jennifer Fisher, a research assistant with Oregon State’s Cooperative Institute for Marine Resources Studies, which works closely with NOAA. Her group goes out on shorter-range, biweekly trips to monitor ocean conditions. The May and June cruises Burke participates in, funded by the Bonneville Power Administration, primarily look at food availability and conditions when juvenile salmon first go out to the ocean.
Still, said Burke, “It’s often not just what’s happening in the ocean, but because the fish live in the river and they are coming out in different conditions each year” — at different sizes, with different fat reserves or parasites — “and all of these aspects of their biology differ from year to year … we can’t just look at the ocean and say survival was really low because of x, y, z. It also matters when they come out and how they are, and those (factors) are driven by freshwater conditions.”