An invasive species is an organism that is not native to an ecosystem and whose presence causes harm to the surrounding environment. Issues arise because invasive species have no natural predators to cull their numbers, nor do the species on which they prey possess any natural defenses against them. In the Great Lakes region, the Environmental Protection Agency has identified at least 25 invasive fish species.
Invasive species are notoriously difficult to eradicate and often continue to wreak havoc upon the ecosystem long after their arrival. Michigan State University (MSU) scientists in the Department of Fisheries and Wildlife are working to develop and implement plans to reduce the number of invasive species to manageable levels and safeguard a natural system critical to the ecology and the economy of the entire region.
Building a better dam
There are thousands of dams in the Great Lakes basin, serving a multitude of purposes. Some provide drinking water or generate electricity; others are used to control the spread of invasive species. Particularly one of the most notorious of the invasive species is the sea lamprey.
Native to the coastal waters of the Atlantic Ocean and found throughout much of southwestern Europe, the sea lamprey is relatively unique among fish. Lacking jaws, paired fins and bone structure, this eel-like creature has remained relatively unchanged for over 340 million years, including at least four major extinction events.
Perhaps the most notable characteristic is its large, disk-shaped mouth lined with rows of sharp teeth in concentric circles. The sea lamprey uses its mouth like a suction cup to attach to prey fish, feeding on their blood and other bodily fluids.
Over the course of their adult lives (between 12 and 18 months), one sea lamprey can kill up to 40 pounds of fish. The sea lamprey was first sighted in the Great Lakes in 1835, in Lake Ontario, where it likely traveled upon the opening of the Erie Canal. In the early 20th century, it spread to Lake Erie through newly improved canals, and soon after, into the remaining three Great Lakes.
There it decimated native fish populations, and opened opportunities for other invasive fish such as the alewife to do the same thing – threatening to collapse the entire commercial fishery. Like salmon, the sea lamprey must migrate up rivers and streams to spawn.
Unlike salmon, it is not driven to return to the exact stream of its birth. Once it reaches suitable spawning grounds, a single female can lay up to 100,000 eggs. In Michigan, many dams are maintained to deny sea lampreys access to spawning grounds.
Coupling the dams with applying a pesticide specifically tailored for sea lamprey to the rivers, management agencies developed an effective practice that reduced their population by over 90 percent from historic peaks. This practice came at a cost. The rivers were artificially blocked from the Great Lakes, disrupting the free and open connection within the ecosystem.
In addition, maintaining the dams and treating the rivers carries a financial cost of approximately $20 million each year. Michael Wagner, MSU AgBioResearch fish ecologist, has been studying sea lamprey in the Great Lakes for over 13 years.
Through a grant from the Great Lakes Fishery Commission (GLFC), he has turned his attention toward developing a new style of dam that prevents sea lamprey from traveling to their spawning grounds while preserving the connection between the rivers and lakes.
“One of the great challenges facing ecosystem management in the Great Lakes is there are competing interests in restoration,” Wagner, associate professor in the MSU Department of Fisheries and Wildlife, said. “One is reconnecting rivers with the lakes, and the other is the necessity of blocking lamprey access to a number of rivers, in order to keep their population manageable.”
Providing fish with ways to circumvent dams has been an ongoing challenge in North American fisheries for 100 years, and in Europe for four times as long. The most common passage is a structure called a fish ladder, a series of stepped pools that fish such as salmon and trout can jump up to get past the dam.
Unfortunately, these are an imperfect barrier for sea lamprey. In addition, other fish cannot jump or swim hard enough to pass over the barrier.
Wagner said he realized his team would have to pioneer an entirely new, selective fish passage that could act as a biological filter, keeping out sea lamprey while allowing other species free access. It presented a significant challenge, but one the team was prepared to address.
“Lamprey have two things going for us that allow us to separate them from other fish,” Wagner said, “First, they swim radically differently, by full-body undulation. That means they can do something no other fish can, which is climb a studded ramp. That gives us a physical way to sort them from the rest. Second, they have a very strong antipredator response that’s driven by only one sense – smell.”
Many fish produce an alarm cue, an odor released when their skin is ruptured, warning others of their species downstream of the attack. In most fish, sensing that odor causes them to slow their movement, reduce the amount of time they spend foraging and look for threats.
Sea lamprey, which migrate primarily at night in dark conditions, use smell, which limits their anti-predator options. Instead of slowing down upon detecting the alarm odor, sea lamprey bolt away from it. Wagner and his team constructed a trial fish passage on the Ocqueoc River in the northeast Lower Peninsula.
They divided the fish passage into two channels – one side that allowed fish free movement upstream and the other ending at a studded ramp only sea lamprey could climb. The team released a plume of sea lamprey alarm odor in front of the open side of the passage, hypothesizing that it would drive the lamprey toward the ramp. It did and the rest of the fish continued through the passage unabated.
“We’re trying to do two things no one has ever done before,” Wagner said. “One is creating a fishway that allows fish to travel through at high numbers and diversity, and the other is to create one that excludes a particular undesirable species. It’s the kind of high-risk, high-reward project I love, and we’re seeing good results so far.”
To determine if the device has wider applications for sea lamprey management, it has to be tested at a larger scale. Wagner has joined a team led by the GLFC to design a large selective fish passage facility at the Boardman River’s Union Street Dam site in Traverse City.
Through a nearly $12 million grant from the Great Lakes Restoration Initiative, the facility will be used to test Wagner’s unique approach to blocking invaders while allowing desirable species to pass.
“Controlling invasive species like sea lamprey is a really hard game to win,” Wagner said. “It’s all or nothing. We’re trying to find a means by which we can help reconnect our lakes and rivers without harming our ability to protect them from sea lamprey.”
Bringing the best ideas to the table
Sea lamprey are far from the only invasive species threatening the Great Lakes. Asian carp, a group of four invasive carp species causing ecological problems in the United States, has been another high-profile invader for decades.
While most came to North America as stowaways in ship ballasts, the grass carp was intentionally brought from eastern Asia to control weeds in aquaculture facilities. The grass carp is now found in 45 states.
They were first discovered to be reproducing in Lake Ontario in 2013, and have since been caught in lakes Erie and Michigan. Seth Herbst, an aquatic invasive species coordinator with the Michigan Department of Natural Resources (MDNR), has been monitoring grass carp in the lakes since they were discovered.
“With grass carp, we’re not seeing the same population explosion we’ve seen in other Asian carp species, but it’s still higher than it’s ever been.” Herbst said. “By feeding on plants, they directly modify the habitats of commercially and ecologically critical native fish species.”
Grass carp can consume up to 90 pounds of plant matter daily, but they only digest about half of what they eat. The remainder is expelled back into the water, where it fuels toxic algal blooms. Lake Erie is the epicenter for grass carp in the Great Lakes, a complex environment in which to study and manage any fish population.
“It’s one of the largest bodies of water in the world, not exactly a confined space where you can easily find and remove the fish you’re looking for,” Herbst said. “It involves multiple states and provinces, who all need to make sure their efforts are coordinated.”
To address these challenges, Herbst reached out to Kelly Robinson and Michael Jones, MSU AgBioResearch scientists with the Quantitative Fisheries Center, to come up with a plan. Starting in December 2016, Robinson led a series of structured decision-making workshops over the course of nine months. She guided participants as they broke down the issue and brainstormed ways to tackle it.
“Structured decision-making is a five-step process that helps you divide a decision into discrete parts, work on each of them separately and then put it back together into a cohesive whole,” Robinson, assistant professor in the MSU Department of Fisheries and Wildlife, explained. “It’s a good framework for working through complex issues in a formal manner.”
Structured decision-making begins with identifying the problem, a step that may seem obvious, but when a diverse group of stakeholders comes together, they often have different ideas regarding the specific nature of the problem.
The group then lays out the values, such as economic or social concerns, that are most relevant to the issue. In the third step, they determine objectives, in this case reducing the grass carp population, and in the fourth, they consider how different management techniques might impact those objectives. Finally, the group reevaluates and reprioritizes their objectives in light of the impacts management techniques may have on them.
What has begun to emerge is an adaptive management plan that would provide fisheries managers with a multitude of tools to control grass carp. Examples include modifying the flow of rivers to make them less suitable for spawning and conducting the targeted removal of fish using methods such as bioelectrode fishing.
Concurrent with the workshops, Robinson’s post-doctoral researcher Mark DuFour has worked to create a grass carp population model in Lake Erie capable of simulating both the size and characteristics of the population, as well as the impacts of the various management practices.
“The Great Lakes are such an important resource for so many people. Anything that could damage them is something we all need to take seriously,” Robinson said. “The plans emerging from these workshops could determine the course of grass carp management in the lakes into the future, and protect the industries and natural resources that depend on them.”
Birds on the brain
Not every Great Lakes invasive species is a fish. In the late 19th century, mute swans were introduced to the United States from their native ranges in Europe. They were brought to adorn city parks and the large estates of the wealthy with their great size and striking white plumage.
Over time, many of these birds left their original confines, whether by escape or intentional release, and began to spread across the nation. In 1919, the first pair of feral mute swans arrived in Charlevoix County in Michigan’s northern Lower Peninsula, marking the beginning of a population that grew by 15 to 22 percent annually until it comprised 2,000 birds in 1990.
That same year, a new population established itself in the southwest corner of the state. Taken together, the MDNR estimates the mute swan population peaked at around 17,500 individuals in 2013, having grown at a rate of 9 to 10 percent every year.
Today, due to control efforts, the population stands at around 8,100. Despite their beauty, mute swans have had serious repercussions on the Great Lakes ecosystem. The MDNR considers them to be among the world’s most aggressive bird species.
Males average about 25 pounds, making them extremely dangerous to humans and native wildlife. They have a history of attacking people, who stray too close to their nests, as well as pushing native waterfowl such as ducks and Canada geese out of their customary nesting and feeding sites.
They pose a particular challenge to common loons and trumpeter swans, both of which are threatened species. Scott Winterstein, MSU AgBioResearch wildlife ecologist, is in the midst of a multi-year project, funded by a $300,000 grant from the MDNR Wildlife Division and additional funding and logistical support from the U.S. Department of Agriculture Animal and Plant Health Inspection Service.
He is studying mute swan population dynamics in Michigan and has determined an efficient, socially acceptable strategy for controlling their population.
“Mute swans present an issue that impacts the ecology of the state, as well as a number of human activities like boating, bird-watching, hunting and fishing that depend on that ecology,” Winterstein, professor and chairperson of the MSU Department of Fisheries and Wildlife, said. “In order to properly address it, we need to get a better idea of what the population looks like and how different management tactics might impact it.”
To return the birds to a manageable level and reduce their potential to negatively impact the ecosystem, the MDNR estimated the population had to be reduced to at least 2,000 animals – about where it was in the 1990s.
Together, Winterstein and MDNR avian research specialist David Luukkonen developed a plan to update the mute swan population model. The old model, largely based on the birds in their native range, did not reflect the realities of their existence in the Great Lakes region.
“Getting a better understanding of mute swan population dynamics here, where they don’t have the same constraints as in their native habitat, will help us develop a more accurate model and better control strategies,” Luukkonen said. “It will also help us avoid unforeseen consequences of those strategies, like if we reduce the number of birds, but the remainder actually reproduce at a higher rate.”
To study the birds in the wild, Winterstein’s team fitted approximately 71 mute swans with solar-powered GPS tracking collars. Every day, the collars automatically transmit their locations through the cellular phone network, giving data on movement without requiring the use of conventional, manually operated radio telemetry technology.
It can also give life expectancy data at various stages of the bird’s life. The team is also monitoring mute swan nests at six sites around the state. Using small programmable temperature sensors planted in the nests, the team remotely records when swans are incubating eggs. This allows them to estimate hatch dates and understand the birds’ reproductive rates.
Randy Knapik, a Ph.D. candidate in the MSU Department of Fisheries and Wildlife, has been collecting data from the nests and collars for the last two years with one more year to go.
“We’re looking at every stage of the mute swan life cycle, from egg to juvenile to adult,” Knapik said. “We’re gathering all the information we can so that we can build an accurate model and make the best management recommendations we can.”
With an accurate population model, the team will be able to determine when and how to apply management strategies – from culling adult birds before they reproduce to oiling nests, rendering the eggs unviable – are effective. Management of mute swans will allow more space for species like the trumpeter swan to gain a bigger foothold in their native range.
“Invasive species aren’t supposed to be here, and usually end up here because of human activity,” Knapik said. “I think we have an obligation to use science to fix that problem.”
This article was published in Futures, a magazine produced twice per year by Michigan State University AgBioResearch. To view past issues of Futures, visit www.futuresmagazine.msu.edu. For more information, email Holly Whetstone, editor, at firstname.lastname@example.org or call 517-355-0123.