A naturally reproduced wild lake trout fingerling. (Photo courtesy of MI DNR.)
The fisheries in the Great Lakes are seeing dramatic changes. In one lake, an invasive species that has become part of the food chain has collapsed. But some native fish are doing better because of that collapse. Lester Graham reports some fishery managers are debating what to do next:
Transcript
The fisheries in the Great Lakes are seeing dramatic changes. In one lake, an invasive species that has become part of the food chain has collapsed. But, some native fish are doing better because of that collapse. Lester Graham reports some fishery managers are debating what to do next:
When we started digging canals, connecting the lakes to the Atlantic Ocean, things changed a lot for the fish in the Great Lakes.
First, the sea lamprey got into the lakes through the Welland canal that bypasses Niagara Falls.
The lamprey is an eel-like parasite that nearly wiped out the big fish in the Great Lakes by attaching to them and sucking the life out of them.
Also slipping through the canals was a smaller fish, the alewife. Since the lamprey wiped out most of the predator fish in the lakes, the alewife population exploded. They out-competed native fish for food. It got so bad, that by the mid 1960s, if you weighed all the fish in Lake Michigan, more than 80% of the weight would have been alewives.
So, once wildlife managers got the sea lamprey under control, they had to figure out what they could do to get alewives under control. The fish biologists decided to introduce new predators, trout and salmon, to prey on the alewives. These fish were not native to the Great Lakes. Expensive nurseries were built by federal and state game agencies to keep supplying new trout and salmon every year to prey on alewives.
Forty years later, in Lake Huron, the alewife population collapsed, and in Lake Michigan alewives are declining rapidly. Mission accomplished, right?
Well, in that 40 years, a whole recreational fishing industry has grown up around fishing for those introduced trout and salmon. Some fishery managers now say we have to find a balance of the right amount of alewives to sustain the introduced trout and salmon fishery. So, recently states have cut their trout and salmon stocking programs to give alewives a chance to recover.
Tom Trudeau [who] operates a fish nursery for the state of Illinois says it would cause trouble to try to take the Great Lakes back to native fish only.
“We do have this industry that we have pressure to keep. You know, you’re putting a lot of people out of business if you get rid of it.”
And Trudeau says because of ecological damage, many of the smaller native fish on which big predators used to feed have been wiped out.
“So, I mean, of the six or seven species in that category, we only have one. And a couple of them are extinct. So, I mean, we could talk about going back to the ideal situation of pure native species, but we’ve disrupted the habitat so much.”
So, the argument goes, the invasive alewives are now needed. But something unexpected happened when the alewives disappeared from Lake Huron. The native fish, walleye, yellow perch, and lake trout started doing better.
Dave Fielder is a fisheries research biologist with the Michigan Department of Natural Resources.
“We’ve long known that adult alewives were a predator and a competitor on newly hatched perch and walleye fry. We just didn’t realize how substantial that effect was until finally the adult alewives were removed from the system and now we’re enjoying some greatly increased reproductive success. Walleye, particularly in Saginaw bay, are at some of the highest levels that we’ve seen in a long time.”
But, after 40 years, people are used to fishing for those introduced trout and salmon. And some fisheries managers are wondering what will happen to all those expensive nurseries that provide their jobs.
What happens to all of those charter boat fishing operations, fishing tourism, if the government were to stop stocking those trout and salmon? Would they switch to fishing for native fish? And, can the native fish even survive in the long-run since so many of the smaller native prey-fish are no longer around?
Dave Fielder says it’s hard to say.
“So, we’re kind of in the middle of a change – it’s really a paradigm shift in many ways – and that’s always scary because nobody really knows how we’re going to end up, but I prefer to be optimistic. I think there are a lot of reasons to be hopeful in regards to the benefits that we’re seeing for our native species.”
But some fisheries managers say the debate of whether to go all native or to try to find the right mix of native and non-native fish is not over. Since invasive species, pollution, and habitat destruction have changed the Great Lakes so much, wildlife managers think they’ll still have to keep stocking one kind of fish or another to keep the recreational fishing industry going. If that’s the case, does it matter whether it’s native fish, or the introduced fish that anglers have grown to like so much?
For the Environment Report, this is Lester Graham.