Travel east, travel west: same fish put to test

As settlers in the United States went west, they took their favorite game fish with them, like Largemouth bass, a favorite of anglers

By Environmental News Network staff

May 5, 2000
Web posted at: 11:49 a.m. EDT (1549 GMT)

As European settlers went west across North America, they refused to part with their favorite game fish. As a result, fish fauna across the continental United States are remarkably similar.

"On average, pairs of states have 15.4 more species in common now than before European settlement of North America," writes Frank Rahel, a fisheries ecologist at the University of Wyoming, Laramie, in today's issue of Science.

Rahel's study is one of a handful of quantitative assessments of the rapid homogenization of Earth's biota, what he calls an underappreciated aspect of global environmental change.

Homogenization leads to the loss of unique, endemic species. This loss of diversity makes flora and fauna more susceptible to disease, which can lead to a faster decline of species.

The homogenization of freshwater fish is a result of introductions for aquaculture and angling, ballast water transfers, aquarium releases, illegal stockings and the extirpation of local populations.

To assess the homogenization of freshwater fish fauna in the continental United States, Rahel examined regional textbooks, journal articles and state databases. Then he compared 1,128 pairs of states to quantify faunal homogenization.

"There was a pronounced increase in the number of species in common between pairs of states," writes Rahel. "In fact, 89 pairs of states that formerly had no species in common now share an average of 25.2 species."

For example, California and Florida historically had no fish species in common. Now they share 26 species. Historically, Arizona and Montana had no fish species in common. Now they share 33 species.

The main factor in the homogenization is fish introductions for angling, Rahel concludes. However, the extirpation of species may soon play a more dominant role.

"For fish, there are about 40 taxa that have gone extinct in last 100 years. There are over 200 additional species that are in need of conservation attention," said Rahel. "My sense is that extirpation could become bigger factor in the future."

The exchange of fish species between states falls into a predominantly east-to-west pattern.

Hatchery production of freshwater rainbow trout created self-sustaining rainbow trout populations worldwide

Game fish such as walleye, bass, sunfish and catfish, all native to the East, are now widely distributed throughout the West. In contrast, only rainbow trout, a western species, are widely distributed in the East.

"The strong east-to-west bias in introductions reflects the colonization history of North America by European settlers and the fact that western waters lacked what were considered desirable game fish," writes Rahel.

The introduction of fish species outside of their native habitat will continue to be a problem in the foreseeable future, he notes.

The source of the introductions has shifted from government agencies to illegal introductions of sport fish, inadvertent introductions through the release of ballast water, and the release of aquarium fish in warm climates.

"Public education is important," Rahel said. "A lot of people think they are doing a favor to individual fish by releasing them when in reality they are doing great harm to the aquatic ecosystem."

Copyright 1999, Environmental News Network, All Rights Reserved

Earth Matters: Fish farming spawns praise, controversy
March 31, 2000
A reward for sustainable fishing
March 27, 2000
New label gives fisheries a fighting chance
March 13, 2000

U.S. biodiversity in jeopardy, study shows
Troubled waters for cutthroat trout
Freshwater species in peril, study finds
Plant diversity slipping away, report warns
Non-native frogs hitch to Galapagos Islands

Science
Frank Rahel
Nonindigenous Aquatic Species
Trout Unlimited

Note: Pages will open in a new browser window

External sites are not endorsed by CNN Interactive.