As glaciers melt, scientists try to figure out how fish will respond

Glaciers in Southeast and around the world are melting. This much scientists know.

About half of the water in the Gulf of Alaska comes from glacial melt, current estimates hold. In Southeast, about 30 percent of all the water flowing from land to sea is glacier melt water.

That percentage is expected to increase due to climate change. But scientists don’t yet know how all that melt water might affect the animals swimming through it.

With the help of a net and a small crew, that’s a problem ecologists Anne Beaudreau and Carolyn Bergstrom have been trying to solve by continuing five years of research this summer. The professors — Bergstrom from the University of Alaska Southeast and Beaudreau from the University of Alaska Fairbanks — have been studying marine biodiversity at the mouths of the Mendenhall, Cowee and Eagle rivers.

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From April through September, the pair have been cataloging which animals prefer the silty water of glacier-fed rivers and which are found more often in terrestrial-fed streams. Their research will provide a baseline from which scientist can tell how marine ecosystems could respond to the melt.

Beaudreau said there’s a hole in scientists understanding of food webs on these river systems.

“This is right outside our backdoor, and yet there’s no research looking into how fish are using these areas, what fish are there,” Beaudreau said. “We know these glaciers are melting, so more fresh water is coming out. If we start to see different types or sizes of fish in different locations, then we can make qualitative predictions on how things could change.”

At low tide on a Tuesday, the pair dragged a net — called a “beach seine” — through the water of the beach on North Douglas. Here, the Mendenhall River empties into tidal waters.

Starry flounder, sculpin and a spawning pink salmon wriggled in the net. Sculpin make up 40 percent of their catch, Beaudreau said. They’ll measure each fish, some of which fit in the palm of a hand, and keep any Dolly Varden for a concurrent study University of Alaska Fairbanks master’s student Doug Duncan is conducting.

As glaciers go away and forests creep in, Beaudreau said, the Mendenhall River estuary could begin to look more like the Cowee Creek estuary: less silt, more sticks and logs. Cowee has about 13 percent glacier cover. The Mendenhall River is around 63 percent. Eagle River falls in the middle at around 48 percent.

Glacier runoff can change a river in two major ways, University of Alaska Southeast glaciologist Eran Hood said. Glacier water has different physical and chemical properties than non-glacier water.

“It’s colder, has a lot more silt, ground-up rock flour,” Hood said. “It tends to have higher concentration of rock-derived nutrients like iron and phospherous. If you change either portion of those you will change the physical characteristics, the light coming in and the chemicals, so over time you’re just changing the physical and chemical template in the food webs.”

• Contact reporter Kevin Gullufsen at 523-2228 or kevin.gullufsen@juneauempire.com.