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Delayed Bristol Bay salmon run? Fisheries biologists say historic record shows no impact of unusually cool summers

 Vessels near the mouth of the Wood River at low tide
Jack Darrell
Vessels near the mouth of the Wood River at low tide

Does the rain and cold this year mean a later salmon run and a delayed season?

That was one of the most common questions posed to Tim Sands, area management biologist with Fish and Game for the Nushagak and Togiak, at the beginning of the 2023 season. Put simply, looking at past run time data, he said the answer is no.

"I've looked at it. And it looks like a shotgun blast to me, I can see no trend that says in colder years, the sockeye run earlier or later than in any other year. Now somebody else might have a different way of looking at it and may have some other perspective, but that's what I got," Sands said.

According to Sands, there are many common misconceptions about run timing, starting with how the run timing is measured. "We look at the run’s halfway point," Sands said, "and I would say that the midpoint of the run hasn't changed much in the Nushagak district over the last several years. I don't expect it to change much."

He believes one misleading factor is with a larger volume of fish, the run may seem earlier. For example, 5 percent of the total Bristol Bay run historically has come in before the last week of June. If that’s a big push of fish, fishers may feel like it’s an early run. As Sands pointed out, the difference between 5 percent of 8 million and 5 percent of 30 million is a lot of fish. It may look like an early run, but the midpoint is the same.

"And that makes people think, ‘wow, this salmon runs really early.’ Well, no. The salmon runs have the same timing. There are a lot more fish earlier, but the midpoint is still the same time," he added.

In fact, run-timing has been surprisingly precise in Bristol Bay over the last century, observable by the climate and run data recorded by the National Oceanic and Atmospheric Administration beginning in the 1950s. That midpoint of the salmon migration back to Bristol Bay has stayed relatively consistent - despite different years of warmer and cooler summers. According to that data, the coldest spring in Bristol Bay was in 1965. But there was no noticeable change in run timing reported that year.

In astatus report written in 1982, Kenneth Middleton, a Bristol Bay Fish and Game biologist, noted that the sockeye fishery had almost invariably peaked, since the late 1800s, in a 2 week period in the first half of July. That was written over 40 years ago and apparently from the 1880s to the 1980s to today, that hasn’t changed much.

Daniel Schindler, fisheries ecologist and researcher with the University of Washington’s Alaska Salmon Program, agrees. He said the data isn’t there to support that the chill in the air in southwestern Alaska is affecting the wall of fish.

"There are those who believe that colder springs delay fish a little bit. But the evidence isn't really strong to support that. Climate conditions just don't translate in a really clean way to run timing," said Schindler.

Schindler posited that the biggest factor that affects run time in Bristol Bay is which district river fish are returning to. The Nushagak and Wood rivers typically see the earliest runs in the bay. But how do salmon decide it’s time to make their journey home?

"Temperature does play a big part there," Schindler said. Not in a seasonal sense, but in the context of millennia. The factors that put different salmon in different districts at different times are complex and still somewhat a mystery, but Schindler said one possible explanation is evolution - salmon adapted differently in response to temperatures of natal streams.

In order to understand these variations, let’s talk about the common life cycle of a salmon for a moment:

We know why salmon return to the same tributaries and lake systems they hatched from, but there is still some mystery in what happens in between.

Starting at birth: salmon hatch from eggs and feed for one or two years in freshwater. Then they depart for the open Pacific Ocean, where they feed on oily, nutrient-dense plankton. They dodge predators and fishing nets, and attempt to gain the muscle necessary to make the long swim back to Bristol Bay. When it’s time, they propel themselves head on against heavy river currents, back to natal streams to spawn and die. Researchers say rather than risk their one shot at unknown or inhospitable waters, they return to the place they know, their ancestral spawning grounds. How do they know where to go? Researchers believe the fish navigate using the earth’s magnetic field like a compass, and their sense of smell - and the bank of smell memory they amassed as a young fish - to find their way back to their home streams.

This means that in Bristol Bay, when stocks hit the mouth of the bay in their massive columns, each is headed to different home lake systems - making them genetically as different as the districts they are bound for.

"The genes are a reflection of the evolutionary processes that these fish have pushed themselves through over the last centuries to millennia. Sockeye that spawn in the Wood River, are genetically very distinguishable from fish that spawn in other rivers," said Schindler.

At the Port Moller Test Fishery, technicians fish a sample net every day of the season and conduct genetic testing and identify exactly where a fish is headed and the strength of the stock. Generally, fish are known to hit the Egegik district earliest before the others start seeing jumpers. For the Nushagak district, technicians say the general rule of thumb is that Nushagak and Wood River fish hit early and Kvichak fish hit later in the season.

And just as that warming spring temperatures in the ocean dictates run time, Schindler said temperatures also tell salmon how long to stay in the lakes, when to spawn, and when to depart as a hatchling. Those water temperature gauges for salmon can be impacted by anything from genetic heartiness to warm waters to disease to competition. In drainages surrounded by steep mountains like Lake Aleknagik, that receive a cooling influx of snow melt, salmon have evolved to spawn in early July. But when streams are warmer, that can have a delaying effect on the lifecycle.

"One of the patterns we see that's pretty interesting is that fish that spawn in warm streams tend to delay entering those warm streams until the fall. And that's probably a behavioral strategy to avoid warm mid summer temperatures. So they hang out in the lake and stay in cool water. And then as things start cooling off, in late August and early September, that's when those fish enter those otherwise warm streams and spawn," said Schindler.

For reasons that are not entirely clear, there is a persistent pressure for most of these salmon stocks to get up to the lakes around the same time.

While management biologists are carefully tracking the run size and trying to answer the unknowns about timing in Bristol Bay, fishers are too, in search of where to cast their nets to haul in the best return on their investments.

Fisheries managers project the time window of the Bristol Bay run as much as possible but agree there is no silver bullet. They are trying answer questions where possible, like how close do salmon get to their hereditary riverbeds, why they resist biological pressures to spawn anywhere else, why they swim so far through a dangerous ocean in the saltwater years, and how climate change will affect the fishery.

Historically, the midpoint in many of the districts occurs the first week of July.

This year, the run on the westside is slightly ahead of where they expected, according to Fish and Game area biologist Tim Sands. That doesn’t seem to be the case on the eastside though, where the run seems to be coming in a few days later than the historical midpoint.

Even as biologists work to answer run timing questions there are no answers until this season’s run makes its return. For fishers and biologists alike, understanding the small window of run timing can feel like one of those picture riddles where the closer you look, the more complicated it gets. And so, for now, the questions and speculation will continue, for this run, the next, and the next.

Jack Darrell is a reporter for KDLG, the NPR member station in Dillingham. He is working on the Bristol Bay Fisheries Report and is passionate about sustainable fisheries and local stories that connect communities and explore the intersections of class, culture, and the natural world.