Invading Species

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What lurks in eastern Oregon waterways?

It’s not just coastal areas where aquatic invasive species wreak havoc. Waterways
in southern and eastern Oregon also have to deal with aquatic critters that
have made themselves at home—invited or not. Sam Chan, an OSU Extension educator
and chair of the Oregon Invasive Species Council, works to understand and combat
these invaders. Below are some of the species threatening eastern Oregon on
Chan’s radar.

Rusty crayfish (Orconectes rusticus)
This creature has made its way to lakes and streams far beyond its native
Ohio River basin. Recently, it was found in the John Day River. How did it
get all that way? Anglers using crayfish for bait may have introduced the species.
Ironically, it’s also possible that students and their teachers, who buy the
crayfish in popular science education kits, have released the animals at the
end of the lesson.

Rusty crayfish are extremely disruptive. They chase native crayfish out of
their burrows, making them more susceptible to predators. They voraciously
eat aquatic plants, fish eggs, and invertebrates, damaging habitats and food
sources for other fish. Humans aren’t immune to their rough-housing: rusty
crayfish have long, strong claws that can injure bare toes.

tui chub poisoning
Tui chub so devastated the native food web in Diamond
Lake that managers used rotenone to kill the invasive fish. Photo by Jim
Craven, Mail Tribune.

Tui chub (Gila bicolor)
Tui chub were introduced to eastern Oregon waterways as live bait. They
feed on the zooplankton that keep blue-green algae in check. Over time, the
tui chub in Diamond Lake diminished the zooplankton enough so that blue-green
algae proliferated in massive toxic blooms. In 2006, the problem was so bad
that officials drained most of the lake and poisoned the remaining water to
get rid of the chub. So far, tui chub haven’t returned to Diamond Lake, but
they have been found in nearby connecting waterways.

Brown trout (Salmo trutta)
Brown trout were brought to the U.S. from Europe more than 100 years ago
for recreational fishing, according to Jason Dunham, an aquatic ecologist for
the U.S. Geological Survey in Corvallis. Since then, the species has flourished
in the Pacific Northwest. Anglers are big fans of the fish, which are stocked
in many lakes and streams. The trout can grow to more than 20 pounds in eastern
Oregon lakes and reservoirs.

But while brown trout thrive in Oregon waterways, they do so at the expense
of native species. Brown trout eat native fish, including threatened bull trout,
and compete with them for food and space. It appears they may also be healthy
carriers of disease that can spread to native fish species. Ironically, brown
trout are listed as “threatened” in their native Europe.

American shad (Alosa sapidissima)
Like brown trout, American shad didn’t get here by accident. When people from
the East Coast began migrating west in the 1800s, Chan says, they found abundant
salmon runs to provide them with food. However, many newcomers preferred
the taste of a fish native to their eastern birthplaces: American shad. There
was so much demand for shad, the government imported the fish and stocked
the Columbia and Willamette rivers with shad in the late 1880s. Now, runs
of American shad on the Columbia River are higher than those of native salmon
species. They have become carriers of seal worms, a parasite that infects
fish and can be passed to humans, and they compete with native species for
food and habitat.

Think you’ve spotted an invasive species? Visit to
identify and report invasives.

Published in: Ecosystems