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Tuesday, May 30, 2023
May 30, 2023

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‘Floating habitat’ could be key for Spirit Lake fish

Researchers seek answers to lake’s post-blast recovery


Longview — For decades, researchers have wondered why Spirit Lake has such enormous fish, even though it apparently contains little for them to eat.

The answer may be tied to the mass of logs floating there as a result of the Mount St. Helens eruption, and it may have implications for lake management across the country. But the reasons might be more complicated — and scientifically controversial.

On an overcast summer morning, professor Jim Gawel hoisted a backpack over his shoulders and headed into the fog across the Pumice Plain, the rock-strewn expanse between the north flank of the volcano and the south shore of Spirit Lake.

Three undergraduate students bounded down the trail ahead of Gawel, eager to see what bugs their floating entrapment tents had caught on the lake overnight.

The bug traps are part of a broader effort to understand how life in Spirit Lake bounced back following the eruption. Spirit Lake today is very clear, Gawel said, which indicates there are relatively little nutrients in the water. And yet the fish are “giant,” and there’s only one species: rainbow trout.

“Here, (the fish) are definitely big, especially for a lake so clear. So what are they eating? We know they are eating a lot of bugs. So what are the bugs eating?” he asked.

The answers possibly could overturn the way humans manage woody debris in lakes, just as other research decades ago discovered the importance of logs in streams and rivers to young salmon.

A ‘floating habitat’

For more than a decade, Gawel has conducted research at Spirit Lake. But it wasn’t until four years ago that the University of Washington-Tacoma lake scientist turned to the floating log mat as a possible answer.

During the Mount St. Helens eruption four decades ago, a landslide barreled into Spirit Lake with so much force that the water surged about 800 feet up the mountain slope north of the lake. When the water rushed back in, it brought with it thousands of trees and debris, forming a large log mat that still floats on the lake.

In the aftermath of the blast, Congress decided to set aside a 110,000-acres area for scientists to study. Everything was left where it fell, including the logs in the lake.

As a result, Spirit Lake is one of the few places in the world where researchers can see the impact of leaving logs in the water for a long period of time. And, over time, the decision could be the reason why life is returning to the lake more rapidly than expected.

Perhaps, as the logs float against each other, they rub off nutrients into the water, Gawel said. Those nutrients could feed plankton, which feeds the bugs, which in turn feed the fish, allowing them to grow unusually large.

“The overall question (of this research) is to understand the ecological role of the logs,” he said. “People see them as objects in the lake that don’t do much. Originally I did, too. But they are a floating habitat.”

Gawel is leading the research along with three colleagues from different schools: Avery Shinneman, lecturer at UW-Bothell, provides the expertise on plankton and lake history; Kena Fox-Dobbs, associate professor at the University of Puget Sound, specializes in isotopes; and Jeremy Davis, senior lecturer at UW-Tacoma, is the “insect guy.”

On this August Thursday, only Gawel was out on the lake with his three undergraduate students. Together, they lifted a small motorboat into the water and stocked it with sampling bottles.

Gawel stood near the rumbling motor and steered the boat towards six white tents bobbing gently in the waves at the other side of the lake.

Earlier that week, the quartet had placed two tents on a log raft, two in open deep water and two in open shallow water.

Each tent had four corners with a tunnel coming out of the top that dropped into a plastic bottle. Insects that emerge as juveniles underneath the tent then climb up the logs and fly towards the light where they reach the funnel through the top and then drop into a plastic bottle containing a 70 percent alcohol mixture.

“They die happy,” Gawel said mildly, teetering precariously on the log raft. “I might be anthropomorphizing a bit.”

Some of his colleagues also had installed sediment traps under the log raft to see what is shedding off the logs and how much.

The bugs sampled from the log raft include mayflies, midges, caddisflies, damselflies and dragonflies. In contrast, researchers primarily capture only midges — small flies — out on open water, according to Jeremy Davis.

Back in the lab, Gawel said they will count the number of bugs and species. In the past, they would dry out the bugs, grind them up and extract the nutrients to measure the ratio.

During the past decade he’s been coming to Spirit Lake, Gawel said the vegetation has returned in the pumice plain and the lake’s chemical signature has decreased since the eruption. But researchers are still trying to figure out the impact of those changes, and sometimes patterns don’t emerge for a long time.

In addition, the log raft has shrunk over the years as the tree sink. Logs once covered 50 percent of the lake, but now they only cover about 20 percent.

Looking at where the nutrients come from and where they end up was a new research question, he said, and it could have a practical application.

“We had to lay the groundwork for everything after that. We are comparing where it is now so we can see where it goes,” he said.

In most lakes, the general practice is to remove downed trees because they are easy to harvest and they can be a hazard for boaters. But then, hatcheries may turn and add nutrients to the same body of water, Gawel said. What if they left the logs in the water as a source of nutrients?

An untouched research location

However, U.S. Forest Service ecologist Charlie Crisafulli challenges Gawel’s hypothesis.

“I respect Jim Gawel, and he’s a good friend, but the logs aren’t the answer,” Crisafulli said.

Before the eruption, the pumice plain was old growth forest and “tremendously productive,” whereas Spirit Lake was nutrient deficient and “incredibly unproductive,” Crisafulli said. After Mount St. Helens erupted, the two ecological systems switched roles. All of the forest material washed into the lake, which became “grossly enriched” with nutrients.

“The fish grow out of that legacy of enrichment,” Crisafulli said.

Despite differing scientific opinions, Spirit Lake — and Mount St. Helens as a whole — provides the ideal research location because it is relatively untouched by outside actors.

“It’s difficult to find a system with little human influence. It draws people in. They care about it,” Gawel said. “We are adding to what people want to know.”

Gawel said he likes to bring students along on his work so they can feel empowered to do their own research. “But I’m not really into grooming students to do what I do. I want to encourage general interest so they can know that they can do it, too.”

Michelle Nguyen, a 32-year-old pre-med student at UW-Bothell, said field work is good experience for any scientific practice.

“You can read a textbook, but it’s not the same as doing it,” she said.

Alexander Barnes, 21, said he plans to pursue a geology master’s degree in England.

“The cool thing about being out here is it’s very interdisciplinary, so I’ve learned a lot of biology,” he said. “It’s a lot of exposure to things that you don’t expect. When you camp out, tons of biologists and geologists come through.”