Species introduction leads to drop in fish diversity, study says
by Randolph E. Schmid
The Associated Press
WASHINGTON - Across America, from lake to lake and stream to stream, more of
the fish are alike.
Diversity is disappearing as species popular with fishermen and cooks are
introduced where they do not occur naturally, fish ecologist Frank Rahel
reports in today's issue of the journal Science.
Rahel calls the process "biotic homogenization," the reduction in regional
differences in plants and animals. Native species become extinct while
popular food and game fish are spread by humans.
"On average, pairs of states have 15.4 more species in common now than
before European settlement of North America," according to his study.
And, like European settlement, the main movement has been East to West,
Rahel found, with one species - rainbow trout - swimming upstream.
Government-sanctioned introductions of game fish have declined in recent
years, but illegal and inadvertent introductions continue.
Rahel, a fish ecologist in the zoology department at the University of
Wyoming in Laramie, studied freshwater fish in the 48 contiguous states,
comparing the number of species each state had in common with each other
state now and in the past. He used historical records to determine past
populations and data from state agencies for current species.
He discovered that 89 pairs of states that formerly had no species in common
now share an average of more than 25 species.
"For example," he said, "Arizona and Montana historically had no fish
species in common, but they now share 33 species."
While much has been written about the loss of native species, Rahel found
that the bigger culprit in this growing similarity is actually the arrival
and establishment of species from elsewhere.
Introductions for food and sportfishing were the major factors, he said, but
he noted that release of aquarium fish and arrival of foreign fish in
ballast water also play a part.
Anglers have had the biggest impact on the movement of game fish from the
East to the West. "Of the 17 most widely introduced species, 12 fit this
pattern," he said.
These include black crappie, yellow perch, walleye, largemouth bass, striped
bass, bluegill and brook trout.
Of 85 fish species found in Nevada, 44 have been introduced and 24 of those
are game fish. More than half of freshwater fish species found in Nevada,
Utah and Arizona were introduced, he found.
And 25 percent to 50 percent of species were introduced in Washington,
Oregon, California, Idaho, Montana, Wyoming, Colorado, New Mexico, Maine,
New Hampshire, Massachusetts, Connecticut and Rhode Island.
Introduced species represented less than 25 percent of the species in the
remainder of the contiguous 48 states.
-- Jay DeLong Olympia, WA
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