Endangered Colorado River fish population surges

Phoenix (AP) – At one time, the Colorado River humpback chub was
losing the battle. Its numbers were falling so significantly that
the federal government declared it endangered. But changes in the
way the river is managed, the removal of predator fish and
drought-related spikes in water temperature have led to a comeback
for the chub.

The population of the endangered fish grew by 50 percent over
the past eight years, the U.S. Geological Survey reported
Monday.

“It may be that the synergy, the combined impacts of all of
those, is the thing that helps humpback chub survive best,” said
Matthew Andersen, a USGS biologist. “We have great confidence in
the population trend. We’re still investigating the reasons behind
it.”

By the end of last year, there were an estimated 7,650 adult
chub at least 4 years old near the confluence of the Colorado and
Little Colorado rivers. That’s up from about 4,000 fish as recently
as 2000.

The chub, named for a protruding hump on its back, can grow as
long as 20 inches and can live for 30 years or more.

Scientists have used the chub as a measurement of the Grand
Canyon’s overall condition in recent years and a symbol for groups
trying to protect the Canyon’s resources.

After Glen Canyon Dam was completed in 1963, the chub’s numbers
in the lower Colorado dwindled because the dam cut off the natural
flow of the Colorado River and thus altered the habitat.

Finding more fish in the river is encouraging, but work remains
to ensure the species’ long-term survival, environmental advocates
said.

“This is not a result that should have us sitting back
comfortably in our chairs,” said Nikolai Lash, Colorado River
program director for the Flagstaff-based Grand Canyon Trust. “It
should have us leaning forward, trying to figure out how to take
advantage of whatever it was that led to a small improvement.”

A decision is expected in the next few weeks in a case the trust
and others filed in U.S. District Court in Phoenix.

It challenges the government’s management of the river and the
chub habitat.

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