Idaho Fish and Game reported on Monday that the treatment to eradicate the Quagga mussels in the Snake River caused a high mortality in some fish species, while others fared pretty well.
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The chelated copper treatment to the six-mile stretch in October was expected to kill many of the species in the impacted area, and the results are in.
Over 4,000 fish were documented during the electrofishing and tagging efforts before the treatment, hoping to provide officials with information about fish numbers by comparing marked vs. unmarked fish during the clean-up.
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Most of the fish that didn't survive the treatment were largescale suckers, northern pikeminnow, common carp and yellow perch. Fish and Game workers examined about 3,500 dead fish in the first few days of the treatment, finding that very few had the pretreatment tags. This led officials to believe there were large populations of the different species in the area.
Throughout the two-week treatment, officials handled almost seven tons of dead fish. Five tons were largescale suckers, and one ton was comprised of common carp and northern pikeminnow. All other fish species make up the rest. Officials acknowledge it is likely that many more dead fish were unobserved.
As far as sturgeon in the area, it is believed they suffered a 100% mortality rate. IDFG reports that a total of 48 white sturgeon were found during the treatment. All are said to have been from hatcheries, and the natural production area was not impacted.
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Largemouth bass, bluegill, and green sunfish appeared to have fared well in surviving the treatment, with low numbers of these species found among the dead fish.
The Niagara Springs area was also found to have larger fish populations than had been detected before the treatment, suggesting that many fish found their way downstream to avoid the copper treatment.
Natural recolonization is expected in the impacted species, though officials will continue to monitor the area to determine if additional stocking efforts will be necessary.
The area will continue to be monitored for several years to collect data on the overall impact of the copper treatment on the area.
