“It’s really hard to kill fish with water,”
says Joe Shannon, a professor of aquatic ecology with Northern
Arizona University. But a recent experiment intended to help native
fish in the Colorado River might have done just that.
In
November, officials from the Grand Canyon Monitoring and Research
Center released a 90-hour flood from Glen Canyon Dam to stir up
sediment from downstream tributaries. The researchers wanted to
redistribute thousands of tons of sand to enhance recreational
beaches and create backwater habitats in which native fish thrive.
But a recent report on post-flood fish counts showed a 63 percent
decline in the juvenile population of the endangered humpback chub,
compared to pre-flood counts. The chub is one of four species of
native fish still found in the Grand Canyon.
During the
experiment, the Little Colorado River — a tributary
that’s the primary habitat of the humpback chub —
surprised researchers by flooding naturally. “Mother Nature can
throw you curveballs,” says Lew Coggins, a fisheries biologist with
the Research Center. The unanticipated weather may have washed fish
downstream — dead or alive — and also created murky
conditions that might have interfered with the post-flood count.
The rare chub might already be beyond salvation: Only
1,000 to 3,000 of the fish still swim in the Grand Canyon. Shannon
notes that there is no scientific evidence to show that sand
displacement would even help the species. Instead, he and other
conservationists say that invasive fish that prey on chub, such as
brown trout, should be eradicated.
He also suggests
managing the river to mimic pre-dam flows. “It’s completely
unnatural,” says Shannon. “The whole thing is completely out of
whack.”
This article appeared in the print edition of the magazine with the headline On the Colorado, a grand experiment meets Mother Nature.
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