Fishing Out Fish Effects

From September, 1996 (Update #28)

The zebra mussel invasion of Oneida Lake seems to be changing the lake's ecosystem, increasing the abundance of blue-green algae, macrophytes and benthic invertebrates, according to Cornell University researcher Edward Mills. However, the winners and losers in the fish community remain unclear, he said. In a Sea Grant-funded study measuring the response of the Oneida Lake ecosystem to the zebra mussel invasion, Mills, Cornell's Lars Rudstam and graduate student Chris Mayer observed that yellow perch are now growing rapidly in their first year of life. "Yellow perch weigh the most they've weighed in 40 years," Mills said. Although this rapid growth appeared at the same time as zebra mussels, Mills doubts that these two events are related. He thinks that smaller populations of yellow perch, which occurred due to factors other than zebra mussels, resulted in faster perch growth. "It's hard to sort out these correlations, but people will have to be patient while we figure out this puzzle," Mills said. Oneida Lake is a particularly good place to evaluate zebra mussel effects on fish because of an unparalleled 40-year data set on fish populations and other ecosystem components, Mills noted. Faster perch growth may be having a negative impact on young walleye, which are not growing as fast. Walleye like to eat young-of-the-year yellow perch. But with yellow perch growing so fast, Mills said, "they're getting out of the window of opportunity for walleye to feed on." It also appears that adult walleye are eating their own young, he said. Mills and colleagues have also observed that macrophyte beds formerly found only along the shoreline now extend into deeper water. That's due to mussel-induced increases in light penetration, they theorize. The macrophyte beds create new habitat for macroinvertebrates and are a refuge for yellow perch, as well as smallmouth bass and sunfish - two species that had not previously been abundant in Oneida Lake. Blue-green algae usually had been present for only two months during the summer in Oneida Lake, according to Mills. In three out of the four years since zebra mussels invaded the lake, these algae have remained from mid-August until November. "Last year Oneida Lake went from the clearest to the most turbid water we've ever seen," Mills said. That turbidity could create the false impression that the lake has been over-fertilized from sewage byproducts like phosphorus, Mills said. However, he believes just the opposite is true. Phosphorus levels have significantly decreased due to improvements at sewage treatment plants. "If you come to Oneida to fish for walleye and end up with another species, you may not be too happy and blame the problem on zebra mussels," he said. "What we're going through is a juggling act. Some species are doing well, others are not. It'll take time to figure out exactly which changes in fish populations we can blame on zebra mussels." Julie Zeidner, New York Sea Grant.

ID: 199609-2.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.