As the Iowa Great Lakes area continues to see growth in the Zebra Mussel population, a report surfaced recently of failed eradication efforts at Christmas Lake, Minnesota. The failed effort at Christmas Lake was not a result of a failure to act quickly or a failure of the eradication techniques used in the containment area. They failed because mussels were likely already established in small, undetectable numbers in other parts of the lake far outside of the containment area prior to the first discovery near the boat ramp.
Research is currently proposed and under way to further develop control and eradication strategies. The newest approved pesticides are only available for spot treatment of small areas around intakes and sensitive areas. Lake wide treatments, especially at the scale of the Iowa Great Lakes, remain unfeasible.
Zebra Mussel Update – Fall 2015
By Mike Hawkins
The zebra mussel population in the Iowa Great Lakes is undergoing rapid expansion. Invading species like zebra mussels have great advantages over native animals as they invade new areas. Because North America has no native mussels or any other animals with similar habitat preferences, reproductive characteristics, or colonization strategies, they can expand very quickly. For example, young native mussels need to attach to specific fish hosts to develop, whereas young zebra mussels develop in the water without needing to attach to fish. In addition, the predators, diseases, and parasites that keep zebra mussel populations in check in their native habitat are missing here.
Zebra mussel population expansion can’t go on forever though. We will eventually see them reach or even exceed their carrying capacity in these lakes. Their population will likely crash and then rebound to a more modest level with less intense fluctuations through time. It is difficult to predict the timeline of these events, but we will be monitoring the population as time goes on.
There have been several zebra mussel news stories coming from Minnesota and Canada in recent months. In particular, the news stories from Christmas Lake have been a bit conflicting. The attempt to eradicate zebra mussels in Christmas Lake last summer was initially reported as a success, but surveys this year in that lake indicate the project was ultimately unsuccessful. To discuss the Christmas Lake treatment and its relevance to our situation requires a description of what probably occurs in lakes during the first years of a zebra mussel infestation.
As we have seen in the Iowa Great Lakes, the transition between the initial discovery of the first mussel to seeing 10’s of thousands of mussels per boat hoist takes about 3 years. In all likelihood, the first discovery of a zebra mussel, in our case a single live mussel in Lower Gar and two shells from a hoist on East Okoboji in 2012, resulted from successful reproduction of adult mussels in the lake. This means the actual introduction of zebra mussels into these lakes may have occurred 1 to 3 years before the initial discovery.
During the first few years, the numbers of zebra mussels slowly grow. This slow population growth is limited simply by the proximity of male and female mussels to each other. A female zebra mussel expels eggs into the water and a male mussel must be very close to fertilize those eggs. Eventually the number of breeding mussels in close proximity to each other increases, population growth is no longer limited, and the lake experiences a population explosion like the one we are seeing on East Okoboji this year.
At Christmas Lake, sampling in 2014 indicated they may have found the first and only early colonizing zebra mussels in the lake near a single boat ramp. The community and Minnesota DNR quickly mobilized a plan and encircled the area with a curtain to keep any larval mussels from leaving that area of the lake. The treatment of the public access area in Christmas Lake consisted of three parts. Zequanox was first applied to the treatment area in September, 2014. That application was followed by a copper treatment of EarthTec QZ in October and November, 2014. In December, a contractor working with the DNR injected 1,000 pounds of potassium chloride (potash) under the ice near the public boat access. The applications of potash and EarthTec QZ were experimental and required special emergency permission.
Initial sampling indicated they had succeeded at killing all zebra mussels within the containment area. However, additional surveys in the summer of 2015 indicated zebra mussels are in other parts of the lake. The failed effort at Christmas Lake was not a result of a failure to act quickly or a failure of the eradication techniques used in the containment area. They failed because mussels were likely already established in small, undetectable numbers in other parts of the lake far outside of the containment area prior to the first discovery near the boat ramp.
Many agencies and communities were monitoring the Christmas Lake effort. It was one of the first times rapid eradication techniques had been utilized after early detection. Many biologists were hopeful for a successful project but also skeptical since undetected colonization beyond the containment area was likely.
Development of an early detection and eradication strategy is still being considered by agencies in the event an introduction, like an infected boat hoist, is reported in the first days after it is in the lake. If caught early, many believe this strategy could be successful and worth pursuing.
The management of zebra mussels continues to be a frustrating endeavor in North America. At least 756 lakes in the United States have become infested since zebra mussels were first discovered in 1988. To date, there have only been a couple of successful eradications.
Research is currently proposed and underway to further develop control and eradication strategies. The newest approved pesticides that are only available for spot treatment of small areas around intakes and sensitive areas include Zequanox and EarthTec QZ. Other research is focusing on parasites and disease identification from areas around the zebra mussel’s native habitat in the Caspian Sea.
Lake wide treatments, especially at the scale of the Iowa Great Lakes, remain unfeasible. For a sense of scale, the volume of water treated at Christmas Lake in the attempt to eliminate zebra mussels was 4 acre-ft (1 acre in size and approximately 4 ft in average depth). The volume of the West Okoboji Lake alone is over 146,000 acre-ft.
Dr. Daniel Molloy visited the Iowa Great Lakes last fall. Dr. Molloy discovered and engineered the bacteria used in Zequanox and travels the country advising communities and agencies on zebra mussel infestations while continuing his own research on zebra mussel pathogens. His message to the resource professionals and the community members he visited with was to continue to slow the spread of mussels to other water bodies, support ongoing and future research efforts to find control and eradication technologies, and to not panic about the infestation.
Obviously, we would be far better off without this invading species in our lakes. With limited options however, we must face this challenge and adjust our habits and the management of the lakes. This will be a learning process for everyone with many unknowns ahead. Our best defense will be to prevent additional invasions and improve the health of our native lake plants and animals. Continuing efforts to improve water quality provides benefits for the native ecosystem which in turn creates better resilience against current and future invaders.