The Lake Trout, the species which was almost driven to extinction by overfishing and Sea Lamprey invasion, has now been restored in the Great Lakes (Image Credit: Cory Goldsworthy, MDNR, CC BY 2.0, Image Cropped)

Back in June this year, I was fortunate enough to attend the 9th International Charr Symposium, a conference which takes place every three to four years focusing on fish in the genus Salvelinus. The conference took place on Lake Superior, a site where the local Lake Trout population had previously been greatly reduced by overfishing and the invasion of the Sea Lamprey in the first half of the 20th century.

Yet the concerted efforts of the State, Provincial and Federal governments’ Fisheries Departments from the U.S. and Canada worked to successfully control the invasive Sea Lamprey species, and the native Lake Trout population was restored. I spoke with Don Pereira, Don Schreiner and Cory Goldsworthy of the Minnesota Department of Natural Resources (MNDNR) and Minnesota Sea Grant (MNSG) about one of the rare success stories of invasion ecology.

Sam Perrin (SP): Overfishing, combined with the introduction of the Sea Lamprey drove the Lake Trout populations right down here in Lake Superior. What was the tipping point, at which people realised stocks were on the brink of collapse?

Don Pereira, former Fisheries Chief, MNDNR and U.S. Commissioer, Great Lakes Fishery Commission (GLFC) (DP): That point was probably even before it started in Lake Superior. The progression of collapsed fisheries went from the lower Great Lakes moving north and west, with Lake Superior being the last holdout, so you could see it coming. But Lake Trout hit rock bottom in the late 1950s.

Cory Goldsworthy, Fisheries Supervisor, MDNR (CG): The first attempt to get coordinated regulation was in the 1890s. There are reports of Canada and the United States coming together and talking about whether we should have restricted fishing seasons for Lake Trout and some other species. But coordination was difficult, whether it was across the lakes or even on individual lakes. It wasn’t until Sea Lamprey invaded and Lake Trout populations were almost obliterated in Lake Superior, that collectively we said we need something bigger.

Don Schreiner, Fisheries Specialist, MSG (DS): Initially the Lake Trout fishery was a commercial fishery. There was hardly any sport fishing at all. The populations started declining quite a bit before Sea Lamprey even hit the lake in the 1940s or so. In the early 60s TFM, a lamprey killing piscicide, became available to treat Sea Lamprey. The initial attitude was, well if the Sea Lamprey are going to kill these fish anyway, let the fishers get them first. But once there was a potential solution, the fishery got closed. So once those streams started to get treated with TFM, there was hope that we could treat the population. Luckily in Lake Superior there were some remnant stocks around, mostly in offshore areas, where Sea Lamprey weren’t well concentrated yet.

So three things happened. Sea Lamprey control came along, very restrictive regulations came in and then stocking programs came on the scene. I think by far, the Sea Lamprey control program was the shining star, but it probably wouldn’t have succeeded if they were harvesting fish as fast as we could put them in.

SP: How low are the Sea Lamprey populations at the moment?

DP: Well they’re ticking up right now in Lake Superior. We’re not sure why, but the last population was about 100-130,000, we think that’s about 5-10% of its peak.

SP: Are there concerns that Sea Lamprey could develop a resistance to the lamprocide?

DP: Oh always. We (GLFC) held a specific workshop to look at any evidence of resistance to the toxin, and there isn’t really any chemical resistance that’s developing right now, and there’s no evidence of that, but these things provide strong selective pressure. So we saw lamprey that were settling out in drowned river mouths, in lentic areas, and evading treatment until we developed another form of the toxin that you could use in river mouths. So there was selective pressure by the lamprey to start to settle out in these drowned river mouths instead of up in the stream, but we figured that one out.

SP: How important was it to get the public onside?

DS: Originally I think it wasn’t that important. The toughest sell was to use the piscicide in the streams. We had to demonstrate that that wasn’t going to kill other fish in the stream or invertebrates. And that’s still a concern.

But I think once people saw the effects of the Sea Lamprey Control program, and that there was hope to get the fishery back, they were very supportive of it. But that changes. People have seen that Lake Trout are back and think “well why do we need to treat the stream”, and they forget about what could happen if Sea Lamprey populations rebound.

DP: There’s a bit of generational naïveté with the young biologists and anglers not being there to witness the collapse and the recovery. So it’s a bit of an educational challenge of the program to make sure that young professionals and anglers are well informed on why control is really important.

DS: Originally one of the control techniques implemented before TFM came along was building barriers in streams to block Sea Lamprey migration and prevented instream spawning. But building a barrier to stop Sea Lamprey also stopped fish migration into these streams.

DP: And that’s become the 600-pound gorilla in the room, because now there are hundreds and hundreds of barriers in streams, and for every larval lamprey we kill with TFM, there are thousands that are never spawned because of dams. Most river ecologists don’t like dams, they want them out, but in some cases, in the lower reach of some of these big rivers, if that dam came out, the lamprey get in. There’s a large dam near Duluth, just east of Thunder Bay Ontario, and some local researchers want it out, because they think the Black Bay Walleye population will do better if that comes out. But that drainage is so dendritic and there’s so much larval lamprey habitat up there, it’ll cost us about a quarter of a million dollars to treat that system and we’d have to go in there every three years to treat it. And it would be hard to treat it effectively. Even if you kill about 80% of the larvae, you would likely see wounding rates of Lake Trout go up.

SP: We’re in a world that is a little devoid of optimism when it comes to removing invasive species. How would you advise people to go about these projects?

DS: In Lake Superior, I think we’re really lucky, because we started with a really pristine system. But the first thing you have to do is identify what the problem is with the fish stock. Whether it’s overexploitation, whether it’s habitat, whether it’s an invader. Then you have to address it somehow. I think it’s important to get the public on your side, because things usually don’t happen cheaply. And the other thing is the expectations of success usually takes about five times as long as what the public would think. Lake Trout restoration took 60 plus years. They’re a long-life species, so they don’t mature until age 10 or so in Lake Superior, so it’s going to take a long time to restore those to the point where people are really excited about it. So I think people need to be patient, you can’t just give up after five years.

SP: Did you have any problems politically?

DP: I don’t think we have politics affect us at that level. I think the need was so critical that it crossed political boundaries. There was a treaty signed in 1955 by Canada and the US that created the Great Lakes Fishery Commission. And the only thing that was clear in that convention was that the two countries will kill Sea Lamprey. It gives that commission a lot of power. They have diplomatic immunity. They come to the local jurisdictions as a courtesy to get a permit. But if we didn’t give them the permit they could still say “get out of our way, we’re going to come in and treat”. But the GLFC works with the States and Ontario in an attempt to make everybody happy.

So the lamprey control program accounts for about 72% of the commission’s budget. But they also help forge partnerships between states. Minnesota and Wisconsin are working on conserving cisco (Coregonus artidae) herring in the west of Wisconsin now, they can come in and help dispute resolution between the two departments.

DS: The GLFC facilitates communication between the agencies, which is really good, because I’m not sure that would always happen otherwise, unless there’s a crisis, and the whole idea is making sure there’s not a crisis. They also fund some research, they have a research and science program, and as an example they’re funding a good portion of this symposium with some of those research dollars. We appreciate that the GLFC is a big sponsor of this meeting.

You can read more about the success of the Lake Trout restoration program here.