Invasion can be slowed, but not stopped

Invasive species have a tendency to stick around, even after they are first detected as a pest and steps are taken to attempt their eradication. 
Be it cane toads in Australia — introduced in attempt to curb beetle grubs destroying sugar cane crops, which dramatically failed and the toads are now spreading like a biblical plague —  or Asian carp — introduced to eat algae in fish ponds, but escaped into the Mississippi during flood events and have a tendency to jump out of the water and endanger boaters — these invasive species have one thing in common: they can’t be stopped from  spreading. Steps may be taken to slow their progress, but wherever a habitat is favourable, they will thrive, breed and displace many native species, since they have no natural predators to check their numbers, or simply overwhelm potential predators by sheer numbers, in their new homeland. 
In Manitoba, zebra mussels are here to stay, which was fully confirmed by the end of August. Initially, Manitoba Conservation and Water Stewardship reported on August 11 that monitoring in the potash-treated harbours and other areas found a small number of larval zebra mussels (veligers). Recent sampling has determined that zebra mussels are present in more areas. On the east side of Lake Winnipeg, approximately six miles from Balsam Bay, 44 veligers and juvenile zebra mussels were confirmed on a piece of floating debris and on rock structures. Winnipeg Beach sample results found 51 veligers inside the harbour and 193 veligers outside the harbour. Gimli and Arnes samples show suspected juvenile zebra mussels. Samples taken from these harbours are being analyzed. Willow Point samples found approximately 24 juvenile zebra mussels. Hnausa samples found about 12 juvenile zebra mussels.
Last fall, zebra mussels were, for the first time, found in Lake Winnipeg in the harbours at Gimli, Willow Point, Boundary Creek Marina/Winnipeg Beach and Balsam Bay. In the spring, the province spent $500,000 on eradication efforts using liquid potash at the affected sites, which we now know was only partially successful in stemming — but not stoppong — the invasion.
Department staff have concluded zebra mussels are reproducing outside the treated harbours in the South Basin of Lake Winnipeg and then entering the harbours.  
“Although the treatments of the harbours this spring were successful and slowed the spread of zebra mussels in Lake Winnipeg, unfortunately there is evidence that a localized population of this highly invasive species exists outside the treated areas,” said Conservation and Water Stewardship Minister Gord Mackintosh. “Further monitoring is taking place for the rest of the open water season and I’m strongly urging fishers, boaters, cottagers and other lake users to remain vigilant and report any findings.”
While the infestation is in its early stages, the province is taking steps by immediately:
• Training the department’s canine unit to find zebra mussels and other species on watercraft for the next boating season, making Manitoba the first province in Canada to permanently use this approach.
• Expanding decontamination unit hours of operation.
• Enhancing monitoring and expanding to more lakes.
• Engaging the federal government for more national assistance at the U.S. border in partnership with the Canadian Border Service Agency.
Manitobans and visitors are being reminded to use the proper four-step cleaning and containment protocol when leaving the lake. Boats should either be cleaned with high temperature and high-pressure water, or remain out of water for at least five days in the heat or 18 days in cooler temperatures, or left in freezing temperatures for three days before launching again.
In order to contain the spread of mussels, the province is also developing new first-in-Canada laws similar to those in Minnesota. This includes laws about transporting water, introducing requirements to drain water before leaving a water body, requiring watercraft to be transported with the drain plug removed and for all water from boat and bait containers to be drained. Enforcement powers and fines are also under review. 
It was just a couple of years ago that zebra mussels were reported to be just across the international border in North Dakota. Earlier, the mussels were found by a local resident at Pelican Lake, Minnesota, about 800 kilometres south of the border. Then zebra mussel larvae were reported to have progressed from Minnesota to North Dakota into the Red River at Wahpeton, where the river begins its northward journey to Lake Winnipeg. It was a mere 635-kilometre leisurely drift on river currents for the larvae to reach Emerson at the U.S.-Canada border. How the mussels actually made their way into Lake Winnipeg is still a matter of speculation. Since adult zebra mussels can survive out of water for several days or weeks, if the temperature is low and humidity is high, they could have been transported on a boat’s hull after it was used in mussel-infested waters, or the larvae could have drifted into Manitoba. Whatever the scenario, they’re here, they’re alive and they’re an extremely serious threat to the lake.
Zebra mussels, a species native to southern Russia, was first noticed in North America in Lake St. Claire, near Detroit, Michigan, in 1988. It is believed mussel larvae hitched a ride in the ballast water of a transoceanic ship. Since that fateful ballast discharge, zebra mussels have rapidly spread across North America.
The prolific and plankton-devouring mussels  use a special byssal gland to secrete highly-adhesive threads that attach it to rocks, debris, water pipes, fishing nets, boat hulls and native mussel species. The attachment ability of the mussels results in bio-fouling — masses of mussels clogging pipes and choking off oxygen and the food supply of other organisms. Researchers from the Great Lakes Environmental Laboratory in Ann Arbor, Michigan, also documented basic changes in the food-chain in the zebra-mussel-infested waters of Lake Huron’s Saginaw Bay. Zebra mussels also release nutrients that encourage algae growth, especially toxic blue-green algae, according to research by the U.S. National Oceanic and Atmospheric Administration. While the toxins secreted by the algae stress native species of mussels, a study has found that zebra mussels are unaffected; thus, they have a free rein to outcompete their competition.
The disruption of the food-chain by zebra mussels can seriously impact Lake Winnipeg’s commercial and recreational fishing industries. Another potential blow to the local economy is that the mussel shells can foul recreational beaches.
As an invasive species, zebra mussels have no native predators other than small- and large-mouth bass and crayfish, which cannot eat enough mussels to make a significant dent in their numbers. 
The experience with zebra mussels in other jurisdictions has shown that disastrous ecological changes can be expected as they continue to spread in Manitoba.