Helicopters, Electrofishers and Bear Data: Mapping Fish in Alaska’s Brooks Range

The tip came from grizzly bears. In late 2017 a National Park Service wildlife biologist who had tracked GPS-collared bears along the southern edge of Gates of the Arctic National Park & Preserve told the Alaska Department of Fish & Game (ADF&G) that the bears were feeding on chum salmon in streams where the state's fish map did not show salmon. That led to a 2018 field survey, described here by its leaders, ADF&G's Nate Cathcart and Joe Giefer, in Alaska Park Science.

The catalog and the program

Alaska law gives special protection to lakes and rivers that support anadromous fish: fish born in fresh water that migrate to the ocean and return to spawn. Qualifying waters are listed in ADF&G's Anadromous Waters Catalog (AWC), which exists as maps and an online application. The five Pacific salmon are the best known, but at least 21 anadromous species are documented in Alaska, including Dolly Varden, Arctic lamprey and sheefish. Dolly Varden, rainbow trout and sheefish can live as either resident or anadromous populations.

The Alaska Freshwater Fish Inventory (AFFI), established in 2002, documents fish in the state's fresh waters and is a major source of AWC listings. Each year it picks an area with many water bodies and little or no fish information, usually flies in by helicopter and makes a rapid, systematic inventory with electrofishers, minnow traps, seine nets and hook and line, recording habitat data at each site.

The 2018 survey

The study area was roughly 400 square miles (1,036 km²) of the upper Koyukuk and Kobuk river basins just north of the Arctic Circle, between the villages of Bettles and Kobuk. Both rivers support subsistence and commercial fisheries: the most recent state report counted 101,772 salmon and 187,465 non-salmon fish taken in subsistence fisheries there in 2014, and about 462,000 chum salmon were taken commercially in Kotzebue Sound in 2017. The Koyukuk's Chinook run has been a Stock of Concern since 2000.

The area also faces development. The proposed Ambler Road would run 211 miles (339 km) from the Dalton Highway to near Kobuk to reach the Ambler Mining District, using a right-of-way across Gates of the Arctic that the Alaska National Interest Lands Conservation Act set up. Good fish data, the authors write, will help agencies, villagers and companies decide about fish communities sensitive to development, land use and climate shifts.

Sites were ranked in GIS by how many miles they could add to the AWC if anadromous fish were found, and the bear data pointed to likely spawning places. Two helicopters carried two two-person crews, which mainly used electrofishing: a current in the water briefly immobilizes fish or draws them toward it, and they are netted, identified, measured, photographed and released. The authors list three advantages: most fish are not harmed, it is less selective than many methods, and it is fast. A raft crew sampled one stream for several miles a day, while the headwater crew sampled four to eight sites of 500 to 1,000 feet each. Aerial surveys looked for spawning salmon, and tissue samples went for genetic testing.

What they found

From July 24 to August 13, 2018, the crews spent 20 days in the field and documented 14 fish species, 13 of them near the proposed road corridor, from 3-inch Alaska blackfish to sheefish up to 3.5 feet.

The work added or extended 41 streams in the AWC, with 481.4 miles (774.7 km) of newly documented anadromous habitat; 12 of the streams are ones the proposed road would cross. Chinook were seen only in the upper Koyukuk basin. A single humpback whitefish, caught at the outlet of Walker Lake, was the first documented in the Kobuk drainage, raising questions about the species' range.

The count is probably low. The crews did not find species known from earlier records, including broad whitefish, least cisco, coho and lake chub, which the authors attribute to timing, effort and location. They focused on streams, not lakes, so seven named lakes need further study. Afterward the team contacted villagers and biologists, which turned up photos of least cisco in Iniakuk Lake and evidence of chum spawning in its tributaries.

Takeaways

Weather was unusually kind: about 20 minutes in rain gear over three weeks, which made flying safe and let crews see clearly into water. Aerial surveys of spawning chum added most of the miles in the headwaters, so future work would fly later in the season, when chum and perhaps coho have reached their spawning grounds. All AFFI data are public through ADF&G's online map.

Sources

• Nate Cathcart and Joe Giefer, Alaska Department of Fish & Game, Fish Inventories of the Upper Kobuk and Koyukuk River Basins, Alaska Park Science 19(1), National Park Service website; rewritten in hubnx's own words. The authors' photographs and maps are left out.