Records of sightings and identifications compiled by government organizations indicate that over 600 non-indigenous species have been introduced to North American fresh waters. Since data has only been collected in the last 30 years, the actual number is probably significantly higher, and the general trend appears to be on the rise according to presentations at The Seventh International Zebra Mussel and Aquatic Nuisance Species Conference in New Orleans, Louisiana earlier this year.

This annual gathering provides a venue for consultants and research scientists to present the results of ongoing research and the impacts of the zebra and quagga mussels on the ecology of North American waters as well as mussel control options for industry. In addition, the conference highlights research on the increasing number of non-indigenous species introductions to North American fresh waters.

The only way to limit these damaging occurences is through improved government regulations and increased public awareness of what can be potentially harmful introductions to the aquatic environment. Unfortunately, only a few states and provinces have implemented comprehensive regulations with regard to non-indigenous aquatic species.

The River Ruffe (Gymnocephalus cernuus), which is an example of a ballast water introduction, continues to spread through the Great Lakes, concentrating within Lake Superior and Lake Michigan. Preliminary study results suggest a significant decline in native fish populations, including yellow perch, following the successful establishment of the Ruffe in an area. An emphasis on better education is essential if we are to turn this situation around.

The introduction of non-indigenous species (including pathogens) through illegal ballast water discharges has received widespread attention. Currently, all commercial vessels entering the Great Lakes are required to complete an open ocean ballast exchange to ensure that exotic freshwater organisms, which may travel from foreign ports, are either flushed out of the ballast tanks or exposed to salinities in excess of their critical upper limit. Obviously, this requirement must be followed to reduce the risk of introduction.

Zebra and quagga mussels have increased their range in North America and are presently found as far as Louisiana, Minnesota, Vermont and Quebec City. Colonization into the western United States appears to have been held in check to date, but may be inevitable. The highest concentrations of zebra and quagga mussels are found within Lake Erie and Lake Ontario at levels which continue to cause problems for industry. Overall, mussel colonization has upset the natural balance of aquatic ecosystems, resulting in fouling of native plants, reduction of phytoplankton abundance, changes in the abundance of certain species of fish and algae, impacts on benthic communities, and changes in water clarity.

Control methods continue to take the form of chemical and non-chemical applications. Most research has been devoted to optimizing existing control options or developing new non-chemical approaches. The use of chlorine is still reported to be the most cost-effective, widely used, and thoroughly understood method of control. The ease of application, low concentrations (drinking water levels of 0.3 ppm to 0.5 ppm) required to induce mortality, and zero discharge requirements, make it one of the safest alternatives.

Formation of dangerous by-products such as trihalomethane (THM) was originally thought to be a concern; however, this is dependent on site specific water chemistry composition. For the most part, this has not been a serious issue in the Great Lakes area. Due to extremely low levels of THM found during the first five years, testing is no longer a mandatory requirement for those industries using chlorine for mussel control in Ontario.

Other effective chemical control methods have included the use of oxidants such as chlorine dioxide and bromine based treatments. The advantages of these infrequently used treatment protocols are as yet unclear; however, testing is in progress.

One area that has gained attention over the past year has been the effective use of non-oxidizing molluscicides (biocides). To date only a few treatments have been undertaken on a trial basis. During the early months of 1997, the Ontario Ministry of Environment and Energy (MOEE) granted approval for the use of one such molluscicide to control zebra mussels. The short duration of these treatments can result in mussel infestation between treatments; however, this treatment can be effective for those water users that can tolerate adult mussels for short time periods. Questions concerning the long-term environmental repercussions of this product, including sediment toxicity and suspended solids loading, continue to be raised by prospective users.

The newest and most surprising discovery has been that one of Canada's most abundant natural resources, potash, is acutely toxic to zebra mussels, and at relatively low concentrations, appears to be selective as a control agent. Ideally, this product is well suited for semi-static flow applications such as fire water protection distribution systems or closed-loop cooling networks. In 1996, the first industrial treatments were completed using this product.

One study, completed at water temperatures of less than 5°C, showed 100% mortality in only eight days, a significantly shorter duration than would be required using most alternatives at these temperatures. Less than two days of treatment is required at water temperatures of 15°C to 20°C.

Apart from the environmentally benign nature of this product, pricing is also an important factor. A trip to your local fertilizer supplier will confirm that on a cost basis there is no comparison between potash and man-made chemicals. The cost for potash required to complete an eight day treatment is less than $1,000.

Non-chemical, control strategies (including physical) continue to gain momentum. The use of in-line fine mesh filters appears to be an easy way to remove veligers from some cooling water systems. Earlier problems concerning frequent backwashing procedures appear to have been resolved; however, high flow situations are still a limiting factor. Testing on these products is continuing.

The use of ultraviolet light continues to attract attention as a viable non-chemical alternative. Earlier research proved its efficacy at low flows. A full scale installation has been completed by Ontario Hydro and testing begins on its effectiveness in 1997. Final results will likely be available early in 1998.

Large scale studies using cathodic or 'electrolytic' protection were undertaken in 1996. This technology is particularly useful on concrete structures that cannot be dewatered for extended periods of time and are not, therefore, candidates for coatings. Results from industrial scale tests showed significant reductions and elimination of older age mussel classes as compared to control samples. Research to fine tune this protocol will continue into 1997.

Another alternative method researched was the use of pulsed acoustics to prevent primary mussel settlement. Earlier reports indicated some promise, and it is felt that this application shows some merit. With further fine tuning, acoustics may provide a cost-effective non-chemical control option.

While very few new protocols were presented at this year's conference, it appears that some technologies that have been undergoing development for a number of years will soon be available for commercial application. 1998 may be a good year for those wishing to look at alternative control strategies.