U.S. Water News Online
DUBUQUE, Iowa -- The zebra mussel has improved fishing in the Mississippi River by clearing the water, but it is hurting other aquatic life, a biologist said.
``They are not, however, a good thing,'' fisheries biologist Scott Gritters said. ``They are a catastrophe. They have made the river clearer but at the expense of 44 species of freshwater mussels.''
That includes the impending extinction for the Higgins' eye mussel, said Gritters, who spoke at a meeting to alert the public to the small, brown mollusks' imperiled status.
Gritters, an Iowa Department of Natural Resources biologist stationed at Guttenberg, said the filtering action of billions of zebra mussels has helped to clarify the water of the Mississippi, which has improved angling for some game fish species on the river.
Always rare, the Higgins' eye was on the federal endangered species list before the recent invasion of zebra mussels.
The U.S. Fish and Wildlife Service last year took the unusual step of placing the Higgins' eye in jeopardy status.
Zebra mussels, exotic invaders brought from Asia to the United States in the ballast of ships, are literally paving over the Higgins' eye mussels, said Gritters, a member of the multi-agency Higgins' eye recovery team.
Another member of the team, U.S. Fish and Wildlife Service biologist Gary Wege, said divers searching for Higgins' eyes last summer had to push their entire arms through a layer of zebra mussels to reach the actual river bed.
The East Channel of the Mississippi at Prairie du Chien, Wis., was once known as the mother lode of mussels, Wege said.
``Between 1995 and 1999, the number of species found there went from 30 to seven, and the overall abundance declined 98 percent.
Wege said he fears the Higgins' eye may soon be extinct.
``We are right on the edge of losing them,'' he said. ``We are not working toward recovery at this point. We are just trying to keep them from going extinct.''
The Higgins' eye recovery team is trying to save the species. Last year, Wisconsin DNR biologists dove to the bottom of the Cassville slough and found 200 living Higgins' eyes, which they cleaned and relocated.
The Wisconsin DNR also is experimenting with raising Higgins' Eye clams in the federal hatchery at Genoa, Wis.
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