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Great Lakes Article:

Zebra mussels still thrive in cool waters of Great Lakes

Article courtesy of the Associated Press
October 25, 2001

MILWAUKEE (AP) -- Spring floods and high summer water temperatures likely killed trillions of zebra mussels in the upper Mississippi River, but the plankton-eating pests still thrive in the cool waters of the Great Lakes, experts say.

The die-off of zebra mussels is good news, but water temperatures are rising and the population may not be quelled for good, the scientists say.

" Although this is a setback (for the species) this year, we think the levels will become problematic again, " said John Sullivan, a water quality specialist with the state Department of Natural Resources.

The mussels likely overtaxed themselves by trying to filter nonorganic material from last spring' s sediment-filled Mississippi River floodwaters, Sullivan said.

The river' s summer temperatures, which reached 86 degrees and above in late August, were too warm for zebra mussels to prosper, Sullivan said. The Mississippi hasn' t been that warm since 1995, when there weren' t as many zebra mussels, he said.

But the zebra mussel population still grows in the Great Lakes, where the cooler conditions are optimal for the species, said Phil Moy, a Wisconsin Sea Grant Institute fisheries and nonindigenous species specialist.

By hitching rides in the bilge of seagoing vessels, the European-native species has infested U.S. waters, first appearing in the Mississippi River watershed in 1991 in La Crosse.

Zebra mussels latch on to native species, hog most of the food and nutrients in the quart of water they can filter each day and leave little for fish and other species that depend on the plankton, said Pam Thiel, a La Crosse fishery resource office project leader for the U.S. Fish and Wildlife Service.

The mussels have a life span of just three to four years, but this year' s death rate was abnormally high, Thiel said.

Authorities looked at native Mississippi River mussel beds in fall and found that beds that had zebra mussels in June were free from the pests.

" They certainly haven' t eliminated zebra mussels, but it will put a dent in the population, " Thiel said.

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