Salmon life cycle remains enchanting mystery

It’s sink or swim, eat or be eaten when smolts hit the ocean.

The conditions there can play an outsized role in how many of them survive to adulthood and return to fresh water rivers to spawn.

But the ocean is a big, mysterious place.

Parts of it can be great for young fish with plenty to eat, and other parts are like food deserts teaming with threats.

On top of that, species use the ocean differently. Steelhead, for instance, quickly head for the open ocean far off the West Coast.

“They blast across the continental shelf and they keep going out,” said Laurie Weitkamp, a fisheries biologist with the National Oceanic and Atmospheric Administration at Newport, Oregon.

Coho and fall chinook don’t do that. Instead, they make a right turn when they transition from the Columbia River to the ocean and meander north.

“(They) tend to hang out just off the coast; they don’t really go anywhere their first summer,” she said.

Spring chinook make that same right turn but then keep going.

“They boogie up to southeast Alaska and all the way across, even to Kodiak, pretty much during their first summer.”

Putting it all together is a complicated puzzle for fisheries managers. The pieces don’t always fit like they think they should.

For instance, many of the adult chinook, steelhead and coho returning to the Snake and Columbia rivers this year arrived at the ocean in 2021.

The times were fat. The water was cool and seeded with nutrients from frequent upwelling – the churning of water from the depths to the surface.

Copepods, tiny creatures at the base of the food chain, were dominated by fat-laden northern species.

Warm water predators were few. It all added up to the second-best ocean conditions in a 25-year span.

On its face, that should mean those 2021 juvenile fish experienced good survival.

While we don’t know if that’s true, fisheries managers expect different results based on species.

Steelhead, the fish that make a furious sprint for the high seas, likely swam right on through those good conditions.

“Conditions in 2021 were really good in our coastal areas. But if you go farther offshore, there was actually a marine heat wave out there,” Weitkamp said.

Fisheries managers are expecting an exceptionally bad steelhead run this year, foreshadowed by a poor showing last year of steelhead that spent just one year in salt water.

Conversely, fall chinook and coho, the species that tend to hang out the most where the ocean conditions were prime, should fare much better.

Spring chinook, which are returning now, may be a different story.

They are the ones that spend some time off the coasts of Washington and Oregon, where conditions were good in 2021, before swimming farther north.

Forecasts call for a modestly good return, at least compared to runs of recent years. Thus far, the fish seem determined to challenge that prediction.

“We haven’t yet seen how it’s gonna pan out entirely,” Weitkamp said. “Certainly, the spring chinook (run) doesn’t look great.”

The run has shown signs of life over the past few days but remains far behind schedule.

“They’re experiencing different conditions, so that’s why some years spring chinook do really well and other years fall chinook do really well. And then some years, both of them do well, but they’re using the ocean differently.”

Where are we going?

However good ocean conditions were in 2021, they began to shift last year and not for the better.

The La Nina conditions of the past few years that produced cold water off the West Coast appear to be sliding toward an El Nino pattern, according to ocean researchers.

In general terms, La Nina tends to be good for Pacific salmon and El Nino, which brings warm water north along with skinny copepods and hungry predators, tends to be bad.

Because copepods from the north are packed with lipids, they can cause an explosion of growth for dozens of species. Those from the south are much more lean.

Since young salmon need to put on fat quickly, Weitkamp said El Nino years can be catastrophic for the northern Pacific food web.

Think of El Nino years producing a salad bar diet compared to the fatty, meat-based menu in La Nina years.

“The whole base of the food chain is based on celery instead of cheeseburgers, and it’s not great.”

Add another layer of complication into the mix: Even in good years, local conditions can conspire to doom a run.

Weitkamp pointed to two examples.

In 1994, researchers were sampling in Vancouver Island’s Barkley Sound. It was the trailing end of an El Nino year, and hatcheries in that part of British Columbia had just released millions of fall chinook smolts.

Weitkamp said a bunch of mackerel moved in and feasted on the young chinook.

“It basically wiped out the entire release of however-many millions of salmon, and if they (researchers) hadn’t been out there, they would have never seen what was going on,” he said.

Example 2 is more recent. In 2017, Weitkamp was sampling chinook in the mouth of the Columbia River.

“There’s plenty of them there. They look fine. They look average, you know, nothing exceptional,” she said. “When we were out in the ocean three weeks later, it was like, ‘Where are they?’ ”

They don’t know what went wrong but suspect a predation event, perhaps by seabirds, hammered the young fish.

What to do?

Fisheries managers like to say humans have little control over the ocean.

True, we’ve spent the past century spewing greenhouse gases into the atmosphere and the ocean has absorbed most of that heat. But reversing that, if possible, will take another century or more.

There are no quick fixes for the ocean. Freshwater is another story.

“I tell people that this is when we really need to double down on freshwater habitat, the parts of the salmon life cycle that we control, making sure that the salmon that go to the oceans are as healthy and as strong as they can possibly be,” she said. “Those are all levers that we have control over and that we don’t know what the winning combination is in any given year.

“So trying to have as much diversity and the healthiest fish possible is our best bet to sustainable salmon fisheries in the future.”

Eric Barker may be contacted at ebarker@lmtribune.com or at (208) 848-2273.