The FBI has a 10 Most Wanted Fugitives list, covering the worst villains on the loose and at large.
Brian Ginn, a “lake doctor” with the Lake Simcoe Region Conservation Authority (LSRCA), was asked about a “Most Wanted” list of invasive species that have made Lake Simcoe their home.
Without hesitation, Ginn put zebra mussels and quagga mussels at the top of the list.
Native to the Caspian-Black Sea region of Eurasia, zebra mussels are believed to have been carried to the Great Lakes in the ballast water of trans-Atlantic ships.
In 1995, the mussels made their way into Lake Simcoe – likely brought to the lake by a recreational boater who failed to clean his vessel or equipment.
Shortly after it was introduced, the population of zebra mussels exploded; that's a typical pattern for an invasive that arrives in a new habitat without any of its natural predators.
Rocks, buoys and piers were soon densely covered with the filter-feeders, that feed on algae – to a depth of about 20 metres. At that point, the substrate changes to mud and silt, materials that clog the feeding tubes of the mussels.
Then, in 2004, monitoring of Lake Simcoe turned up the first quagga mussels. Also from the Caspian-Black Sea area, quagga mussels are believed to have followed a similar pathway to Lake Simcoe.
The LSRCA monitors mussel populations at 51 sites across the lake and discovered a surprising trend. Since 2008, Ginn said, “Zebra mussels are almost gone. They’ve almost been totally replaced by quagga.”
Quagga mussels need less food than zebra mussels, are active at lower temperatures and have “no problem” feeding in the fine sediments below 20 metres depth. As a result, they are found throughout the lake.
Quagga mussels may have actually increased biodiversity, Ginn explained, noting they provide additional food for benthic (lake bottom) organisms, and a food source for some fish, notably whitefish.
The LSRCA is still monitoring the effects on native fish species.
Here's the rest of the Most Wanted Invasive Species:
Rusty Crayfish. The Rusty Crayfish is native to the Ohio River basin and was likely introduced to Ontario by anglers as bait.
An aggressive species, the Rusty Crayfish has been able to outcompete native crayfish; it can even fight off predators, including fish.
Preferring shorelines and shallow water, it feeds on vegetation voraciously, according to Ontario’s Invading Species Awareness Program, reducing the spawning and nursery habitat of native fish and contributing to the spread of aquatic weeds like Eurasian milfoil.
Details of its spread and impact aren’t well understood.
“There haven’t been too many studies in Lake Simcoe,” said Ginn. The crayfish are elusive and hard to trap – but they are known to be established in the Beaverton area.
Spiny water flea. The spiny water flea is a tiny free-floating crustacean, less than 15 mm long. Native to fresh water in Northern Europe and Asia, it is another accidental introduction to North America, first spotted in the 1980s.
It turned up in Lake Simcoe in 2004. Then suddenly, said Ginn, “there were a lot of them.”
Spiny waterflea has a long barb that can protect it from predation by small fish; it is itself a major predator of other zooplankton that are food for native fish species. And it reproduces rapidly.
Again, monitoring showed an initial spike in Lake Simcoe followed by a sudden decline in numbers and then a levelling off. Why?
“Nobody’s really sure,” said Ginn. It may be that growing numbers of mature cisco (lake herring) have been feeding on spiny water flea.
It all points to the fact that “lakes are complex,” Ginn said and that invaders, after an initial explosion in numbers, may end up finding a place in the food chain.
The Round Goby. First found in the Pefferlaw area, the Round Goby is a bait fish from the Black Sea/Caspian Sea area that escaped into the wild.
Efforts to prevent their spread to Lake Simcoe were unsuccessful. Round Goby has been found in the lake since 2006 in large numbers. A benthic species, they have apparently replaced some native fish species like the Sculpin.
But again, there has been re-balancing of the food chain. Although Round Goby compete with native fish species by eating insects and other benthic organisms, and adults are known to eat the eggs and fry of other fish, Round Goby also feed on zebra and quagga mussels, said Ginn, “and they’ve been incorporated into the food web. Bigger fish are eating them.”
Others on the list of top invaders include plants like Eurasian Milfoil, Curly-leaf pond weed, and Starry Stonewort.
Starry Stonewort is actually an alga native to Eurasia. It forms dense floating matts, destroying fish habitat and food sources and interfering with boaters, swimmers and other recreational uses.
Even the smallest fragments – stuck on boats, ropes, canoes, and footwear - can reproduce, spreading the invader.
Fighting invasive species involves public education: boaters, not recognizing Starry Stonewort, spread the problem plant unwittingly when they removed the matts of algae fouling their motors and simply threw them back in the lake. It also requires monitoring to determine the spread and the impact.
“We’re doing an annual plant monitoring program,” said Ginn and working with the Starry Stonework Collaborative for the Great Lakes Basin on management strategies.
The list of invaders includes fish species, like Common carp and goldfish, and introduced diseases like Koi Herpesvirus, blamed for huge die-offs of carp in Lake Simcoe in 2008 and viral hemorrhagic septicemia (VHS) virus.
What is the role of climate change in all of this?
“A lot of these species are more adapted to warmer water than the native species,” explained Ginn.
As water warms, there will be more adjustments to the food chain and the balance of species and, likely, more introductions.
The Lake Simcoe Watershed has recognized 51 invasives – 32 on land, 19 in the water, said Ginn.
But the number is expected to rise. A total of 182 invasive species have been identified in the Great Lakes basin “so there’s a lot more that could get here.”
Among the new threats to watch for: Water Soldier (successfully eliminated when it was found in the Trent River), Water Chestnut, Hydrilla (an aquarium plant now banned) and red shrimp.
It’s “probably just a matter of time” before these and other invasive species make their way into Lake Simcoe, said Ginn.
“This is one reason why monitoring is so important” and why prevention is critical, Ginn explained.
Keeping the invaders from reaching the lake in the first place is more effective than trying to control them.
“Once they’re in the lake, they’re almost impossible to get rid of,” Ginn noted.
That’s where residents and visitors to the lake can play a role, by taking certain simple precautions.
Never dump aquarium species – from hydrilla plants to goldfish – into natural water bodies.
If you are a boater, clean boat motors and bilges using a power washer and make sure that all boat parts are drained and dry before moving to a new water system.
Zebra mussels and quagga mussels can survive up to seven days in the open air; their larvae can survive up to one month in a damp bilge, Ginn said. That makes proper cleaning and drying vital, when planning a move from waterway to waterway.
Anglers are reminded to never transfer bait between lakes and never dump unused bait.
The general public also has a role to play in the tracking of invasives. See something odd? Take a photo, and send it to the LSRCA or to www.invadingspecies.com/report , Ontario’s invasive species site. You can also call the Invading Species Hotline, 1-800-563-7711 or use EDDMaps Ontario, an app available from Google.
Ginn noted that when starry stonewort first appeared in 2009, wrapped around boat motors, boaters unwittingly transported the invader from water body to water body: they simply didn’t recognize it for what it was.
Getting familiar with the “most wanted” list of invasive species can be a step toward preventing them from spreading, Ginn said.