Posted by Chris Larsen on 2nd May 2023
Sea Lampreys In The Great Lakes
Ross Shaw from the Great Lakes Fishery Commission joined the Great Lakes Fishing Podcast for Episode #103. We discussed sea lampreys in the Great Lakes including how they were introduced, how they’ve affected the fishery, and what’s being done to stop the spread of sea lampreys.Sea lampreys have been around for more than 340 million years and have survived more than four major extinction events. That's astounding. What makes sea lampreys so adaptable?
Ross Shaw: Their lineage dates back 340 million years. So, even though sea lampreys are fish, they aren't exactly what you would think of when you think of a stereotypical fish. It looks almost kind of like a water snake combined with an eel. But unlike most fish, these guys don't have any paired fins. They don't have bony jaws. They're all cartilage. Those evolutionarily early adaptations in their body are what makes them such an adaptable species. They were native to the Atlantic Ocean and then invaded through the manmade shipping canals in the early 1800s, and then they were only in Lake Ontario for a while because they couldn't get past Niagara Falls. But once the Welland Canal was widened and deepened in the early 1900s that gave them an easy path right around the falls. Essentially, it was open season on many of the Great Lakes' commercial recreational and tribal fisheries. So, lake trout, whitefish, and pretty much anything that the sea lampreys could get their mouths on.
Once they were able to clear those falls, how fast did the sea lamprey population grow? How did that happen?
Ross Shaw: They were first in Lake Erie, but the problem wasn't noticed because the fishery wasn't as prominent. I believe that was primarily due to the industry that was along the waters there. So, there were not a whole lot of great habitats for the sea lamprey to establish there. And it wasn't until they reached Lake Huron and Lake Michigan that they started to do some damage and people started sounding the alarm on the sea lamprey invasion. By 1938, sea lampreys had reached Lake Superior, and the problem had come to almost nearly peak. At that point, the commercial and recreational, and tribal fisheries as well as coastal communities that depended on these fishing operations started sounding the alarm and talking to elected representatives to get both the United States and Canada to come together to deal with the sea lamprey problem.
What was that collaboration like?
Ross Shaw: Sea lampreys do not obey boundaries. There are six or seven Great Lakes US states, as well as two Canadian provinces that surround the Great Lakes Basin and many different tribal nations. So, there are many different jurisdictions around the Great Lakes. Because the sea lamprey problem was so pervasive and caused such a disruption to day-to-day life both the governments of the United States and Canada realized that they would have to come together. They weren't going to be able to handle this piecemeal like they previously did, having each jurisdiction handle things on its own and not communicating with other jurisdictions. They realized that they needed to come together and form an entity to work across the borders, and that's when the Great Lakes Fishery Commission was established… in 1955 when both the US and Canada finally came together to tackle the sea lamprey problem.
It's been almost 70 years since that happened. People today know that they're there and they know that they affect things. But can you paint the picture of what it was like in the 40s and 50s? How much of an effect was it? Can you put some numbers to that?
Ross Shaw: One of the sea lamprey’s favorite prey species is the lake trout. The annual commercial lake trout catches in Lake Huron and Michigan were around 5 million kilograms in the 1940s, and that dropped to nearly zero in the late 1950s. Lake trout were almost extirpated or eliminated from four out of the five Great Lakes, every lake except Lake Superior. The only reason they were still in Lake Superior is because that's the last lake that they(sea lamprey) invaded. It’s also the first lake where sea lamprey control was started. Lake trout, lake whitefish, and all these enormously important commercial and recreational fisheries were decimated. Of course, the associated coastal communities that depended on tourism that got money from marinas and other things like that, were also decimated.
What is the life cycle of a sea lamprey? How long do they live, and what are the different stages?
Ross Shaw: It's hard to put an exact number on how long sea lamprey will live. They hatch from their eggs, and then they go into what we call larvae or seeds. So, that's when these guys are small, about the size of your pinky, maybe even smaller. At that point, what they're going to do is swim downstream and into the stream bed. They're going to filter feed. So, at this point, they're essentially harmless. They're just buried in the stream bed filter feeding on phytoplankton, zooplankton, and other organic material in the environment. They're going to be in that stage from anywhere from three to five, and sometimes even up to as much as 10 years.
So, that stage really kind of throws a wrench into the calculation of how long sea lampreys live. That is the stage that primarily affects its lifespan the most. But after they spend that time in that larval stage, what they'll do is metamorphose. That's when they're going to develop eyes and that sucker mouth that everyone is so familiar with. That's when they'll swim downstream and begin their parasitic feeding phase. That's when they're going to go and do their damage. They're going to go out into the lakes and start feeding on fish. Each sea lamprey in that 12 to 18 months of their feeding phase is going to kill about 40 pounds of Great Lakes fish. After they're done feeding on fish, they turn into what we call the spawning adult.
Their digestive tract will shut down and they'll be focused on spawning and spawning only. What they're going to do is find a stream that has a good spawning habitat, and actually how they find that is super interesting. After they hatch and are buried in the stream bed, they actually excrete what's called a pheromone. It's this natural scent that they excrete and then this flows down the river out into the lakes. That's how sea lampreys in part, determine which streams they want to go to spawn. By smelling those freshly hatched larvae, they can determine that, oh, there's some good spawning habitat up there. Once they find a good stream to go up, they'll swim upstream. Then they make rocky, horseshoe-shaped nests.
Once they have made that nest, they'll intertwine. One will latch on top of the other and then the bottom one will latch onto a rock. They'll intertwine, wiggle, and then they will release their sperm and eggs downstream onto that rocky horseshoe-shaped nest. That's when the eggs will hatch and then the sea lamprey will die after they spawn. So, they kind of are similar to salmon in that way. That's part of the reason that once they're done feeding, they're focused on spawning and spawning only. That's because that's their essential goal in life. Once they're done feeding, they have one thing and one thing only, it's going to be spawning and dying. So, all said and done, we estimate it's about two years on top. However, that larval phase can be as little as five years to as many as 12 years.
Sea lampreys are native to the Atlantic Ocean. Fish in the Atlantic Ocean have built a defense against sea lamprey attacks that Great Lakes fish don't have. How do sea lampreys affect ocean fish when they attack them?
Ross Shaw: What the single lamprey will do is, if you see its mouth, it has over 150 razor-sharp teeth and a sucker mouth. They use that sucker mouth to latch onto the side of the fish, and it has a suction cup around the outside of his mouth. So, it latches on. It uses those over 150 razor-sharp teeth to dig into the side of the fish's flesh, and then in the center of the mouth here, you can see what's called the rasping tongue. And so that's what does the damage. Once they're attached to the fish, they use that rasping tongue to gnaw and bore a hole through the fish's scales and into its flesh. Once it's created that hole and the blood starts slowing, it's going to excrete an anticoagulant to prevent the blood from stopping.
The sea lamprey will sit on that fish and feed on it for as long as it wants. So, most of the time a sea lamprey will kill the fish that it's on. But if the fish does survive the seal lamprey attack, the sea lamprey will leave a nasty wound. That wound oftentimes becomes infected and will cause the fish to die or it'll make the fish more susceptible to predation. So, most of the time, if a fish is attacked by sea lamprey it's more often than not going to succumb to its wounds and die. So, we estimate about six out of every seven fish that are attacked by sea lamprey eventually die.
They are very lethal. Part of the reason they're so so problematic here in the Great Lakes is that out in the Atlantic Ocean, they have co-evolved with the much larger fish. So, they're feeding on fish the size of a tuna, or a shark. These are significantly larger fish and those smaller wounds that they're leaving on the fish, they aren't going to be killing that fish. It's more like a leech where it'll drink your blood and it'll come unlatched. It gets what it needs. It drinks your blood. But then you're left essentially harmless. You have the wound, but the wound heals over.
But when it's in the Great Lakes, think about the fish that it's feeding on. Think about a lake trout or a white fish. Those fish are magnitudes of times smaller than tuna and have not co-evolved with sea lampreys that are from the Atlantic Ocean. The wound that normally wouldn't be a problem on an oceangoing fish like a tuna is going to be much more problematic because of much higher mortality on the native fish here in the Great Lakes compared to those in the Atlantic Ocean.
We’ve been talking about lake trout, salmon, and whitefish. What other Great Lakes fish species are susceptible to sea lamprey attacks?
Ross Shaw: Part of the reason sea lampreys are so destructive is they are willing to eat just about anything that they can get their sucker mouths on. Scientists have proven that sea lampreys will have a preference for lake trout. But in the absence of those preferred species, they will attach to anything. They have attacked and killed fish as large as sturgeon to things as small as perch, bass, and walleye. They don't have a preference they just want something that has blood. If they can get their mouths on them they're happy with it.
How big do sea lampreys get?
Ross Shaw: On average, sea lamprey will grow 12 to 18 inches long. But in the Atlantic Ocean, where they're feeding on much larger fish, they'll get about two feet long. So, they do get significantly bigger in the Atlantic Ocean.
Do sea lampreys attack humans?
Ross Shaw: That is probably our most asked question and I'm happy to report that you can swim without fear. Sea Lampreys will only attack cold-blooded creatures. Fish, as we know, are cold-blooded creatures. Sea lampreys can detect what type of blood a particular organism has, and they will only attach to cold-blooded creatures. There have been stories from back during the peak invasions of the early 1900s. Supposedly, somewhere there was a swimmer, a woman who swam across Lake Ontario. The news headline was “Woman Emerges from Lake Ontario Covered In Lampreys.” While that probably did happen, I'd say the more likely cause of them attaching to that particular person was that they were more hitching along for the ride than actually drinking that person's blood. They are not interested in warm blood.
How are sea lampreys being dealt with on other bodies of water, such as New York’s Finger Lakes?
Ross Shaw: We have an entire division devoted to treating steel lampreys over in the Finger Lakes, our folks at the US Fish and Wildlife Service out in Vermont. We have a dedicated source of funding specifically for fighting sea lampreys in the Finger Lakes.
What Is being done to control sea lampreys on the Great Lakes?
Ross Shaw: We primarily use two control methods. The first one is what we call lampricides. So, what this is, it's a selective toxicant that we apply to streams where we know that there are high concentrations of those larval lampreys. We have our partner agencies at the US Fish and Wildlife Service here in the States, as well as the Department of Fisheries and Oceans over in Canada. Those are going to be our partner agencies who are going out and conducting the fieldwork. They send out agents with electrofishing backpacks. They kind of look like Ghostbusters. They have these little electric paddles that go out into streams. They'll tickle the sea lamprey out of the stream bed, and then depending on how many larval lampreys they find, they can use that data to extrapolate and determine the relative abundance of all the lampreys in that stream.
Once we determine which specific stream has the highest concentrations of lampreys what we'll do is we'll decide if this will be a good candidate for treatment. Once we're ready to apply the lampricide, we'll go up as far up the stream as the sea lampreys can get. Most oftentimes this is the first barrier up the stream. Whether it's a purpose-built dam to block sea lampreys or something like a hydroelectric dam. We'll go up to where we know they will not be able to get above, and then we'll just treat the stream down from there. We have these lampricides and what we'll do is we'll apply it at a very small concentration.
You're looking at the order of three to five to seven parts per million. Very, very small amounts. It's applied as a liquid via a perforated tube across the stream. We'll also go into little streams and creeks and tributaries and also apply different forms of this lampricide, sometimes in the form of just blocks, and just put those in these slow-running streams to let them slowly dissipate. We want to make sure we get every possible way into that river and out of that river to make sure all the lampreys that are going to be escaping this amid treatment. This is by far our most effective and efficient control method. But the downside to this is that it is extremely expensive.
We have to be very specific and very strategic about where we're going to apply the lampricides. The other control method that we use in concert with lampricides is barriers. These can be barriers that are purposely built to block lampreys or they could be any barriers that have a different function but also happen to block sea lampreys. Barriers help us limit the amount of stream miles that we have to apply the lampricide in.
Traps are another method we use to remove sea lampreys from streams. However, traps are not as efficient. They aren't so efficient that we classify them as a control method. So, primarily what we use traps for is for assessment purposes. What we'll do is we'll put these traps oftentimes at the base of dams and other barriers and then based on how many lampreys we get when they come upstream to spawn we can use that to help us determine the size of the sea lamprey population. Lampricides and barriers are the two primary control methods. But the Fishery Commission is investing a substantial amount of money into research into other control methods. For example, one interesting possible control method that is being explored is what we call pheromones.
So, I mentioned a pheromone that the larvae excrete to tell spawning sea lamprey there is a suitable spawning habitat. Some of our scientists have determined that sea lampreys have what we call an alarm cue, what we call a repellent pheromone. That pheromone that I talked about, that the larvae excrete, that's what we call an attractant pheromone. The larvae will excrete it, and then the lampreys come towards it. This alarm queue is what we call the repellent pheromone. As the name implies, it repels the sea lampreys. So, that's excreted by dead or dying sea lampreys to tell them to get out of here, you don't want to be here. There's a predator or something else that could put you in danger nearby.
And some of this research is looking into seeing if there are ways where we can use those attractant and repellent pheromones to improve that trapping efficiency. As I mentioned currently trapping isn't efficient enough to the point where it's making a substantial indent on the populations. Let’s say we have a fork in a river, and this is a really good spawning habitat and this side is a trap. We don't want them to go to the good spawning habitat. So, we might apply that repellent pheromone on that side of the creek and then put the attractant pheromone on the other side of the creek to help encourage them to get into the trap and increase that trapping efficiency. So, it's super interesting stuff and our researchers are doing great work. It'll be very interesting to see how lamprey control evolves in the coming decades.
Do people eat sea lampreys?
Ross Shaw: It's funny you mention that. When they first invaded, that is probably one of the first control methods they tried. There's a very famous picture of someone with some sort of spear or fork above a pot and they have kind of a disgusted look on their face. As the story goes, for people that have tried to cook them it's just quite frankly, disgusting. So, by all accounts, the meat is gray, mushy just otherwise, visually and taste-wise, unappetizing. We've had people that have tried to smoke them, people that have tried to fry them, and they still don't taste good.
In my opinion, if you're frying it and it still doesn't taste good, then you know something's wrong. So yes, they have tried to eat them, but unfortunately, they are not seen as a good species to eat. On top of that, even if they were edible you wouldn't want to eat the ones in the Great Lakes specifically, because they have high concentrations of heavy metals. So, some of these apex predators that they're feeding on like lake trout are accumulating heavy metals by eating the smaller fish. When the sea lampreys are drinking from those apex predators’ blood and bodily fluids, they're getting almost all the heavy metals straight into their system.
Since they have high concentrations of heavy metals, you wouldn't be able to eat them, even if you wanted to. I will say that over in the Atlantic Ocean, specifically in Europe, on the eastern coast of the Atlantic Ocean, lampreys are considered quite a delicacy. If you went to a restaurant and they had for fish that are market price, sea lampreys are that kind of fish. I know the Queen of England also makes a ceremonial lamprey pie every so often. So, it's not eaten here in the Great Lakes, and we don't want it to be eaten here in the Great Lakes. But if you wanted to, you could go over to Europe to see if you can find yourself some lampreys.
Do Great Lakes fish eat sea lampreys?
Ross Shaw: If fish did prey on sea lampreys, it would be in that larval stage where they're small and easily susceptible. As far as we understand, there isn't an established predator-prey relationship where fish are feeding on lamprey larvae so much that they're affecting the population. That's not to say that it couldn't happen. I would expect it to happen if a fish is right by some lampreys swimming out of their burrow. But as far as we understand, and as far as we've seen, there is no established predator-prey relationship. After we do these lamprey site treatments, and on some of these larger treatments we're killing lampreys on the magnitudes of millions or hundreds of thousands, they'll be floating all around the river and then you'll see fish come and eat those dead lamprey or seagulls will come down and eat them. So, they will feed on them opportunistically. But as far as an established predator-prey relationship it's not something that we've seen.
What would happen if we stopped lamprey prevention strategies? How long would it take before they took over again?
Ross Shaw: That's a great question. If we did stop, for example when we did in 2020, if you're not able to go out and treat, you're not going to see the effects immediately. So, the next year, because of that larval stage, they're going to be in that larval stage for anywhere from three to five years. It'll probably be about three or four years before you see a significant uptick in the population. We have done that previously. I believe it was the nineties when for whatever reason we were experimenting with stopping sea lamprey control. Within less than 10 years, we had seen a substantial uptick in lake trout wounding. You saw a decrease in the lake trout population.
So, you wouldn't see it immediately. But four or five years down the line, you would see the effects. You'd see more scars on the fish that you're catching. You would see decreased fish population numbers. Even though it's not something, you'd see an immediate effect of, it's something that needs to be ongoing. Even though we've reduced the sea lamprey populations by over 90% compared to the historic highs in the 1940s and 1950s, the sea lamprey is still out there. They are so widespread throughout the Great Lakes that we are sending control teams out there every single year to treat the most infected streams. if we stop that, the effects on the Great Lakes fishery would be enormous.
When they first invaded, they almost wiped out lake trout from the entire Great Lakes. The Great Lakes fishery in general has nearly been destroyed thanks to lampreys as well as other factors such as overfishing habitat destruction and pollution. But now, thanks to, in part, sea lamprey’s control the Great Lakes fishery is valued at over $7 billion. Even though you wouldn't see that immediate effect on the Great Lakes fishery, you would see it in four or five years. I think you'd quickly find out that you need to continue lamprey control.
How deep can sea lampreys swim in the Great Lakes?
Ross Shaw: Most of the time, they're going to be hanging out in the deeper parts of the water. They prefer the colder, dark parts of the Great Lakes. What's interesting about that is they will change the color of their bodies depending on what type or stage of their lifecycle they're in. When they're out in the lakes, down in the deeper parts of the water, they're going to be almost black or dark gray. Once it's time to spawn, they're hanging out in the shallow parts of the water, the silty streams. They're going to turn brownish-yellow. So, that's another reason sea lampreys are not attacking humans. If you're diving down into 100 or 200 feet of water you're going to see lampreys. But lampreys are not going to be swimming near the beach. They're not going to be like sharks coming up to you. Sea lampreys are only hanging out in the deeper parts of the water column.
What should you do if you catch a fish with a sea lamprey on it?
Ross Shaw: The first thing is to ensure that it is a sea lamprey. What a lot of people fail to realize is that in addition to the sea lampreys, there are actually four native species of lampreys in the Great Lakes. They're pretty easy to tell apart because the sea lampreys are going to be significantly larger than most of your native species. Only two of the four native species are going to be parasitic or attach to fish and drink their blood. Once you confirm that it's a sea lamprey, just cut its head off. Cut its head off and throw it back in the water. Chop it up. It doesn't matter how you do it. Just make sure it doesn't go back into the water alive.
Is it safe to eat a fish that has a sea lamprey bite?
Ross Shaw: It is safe to eat. People prefer to cut around the scar, so you don't necessarily see that on a filet that you're eating. But it is safe to eat.
If you want to know more about sea lampreys, you can go to the Great Lakes Fishery Commission website at glfc.org or watch the video below.