Managers of salmon in Lake Michigan must soon decide how many fish to put into the lake each year. The salmon fishery is a man-made industry in the Great Lakes, produced by planting millions and millions of fish in the lakes. Keeping the salmon population in balance with the food supply is a challenge these days. Some scientists are raising new questions about the salmon's demise in Lake Huron and whether it can be stopped in Lake Michigan.
Lake Huron fishery collapses
Salmon were brought to the Great Lakes from the Pacific Ocean. Some fish have learned to breed in the wild here but historically if you caught a salmon in the Great Lakes, it was born in a tank. By 2002, that was no longer true in Lake Huron. That year researchers observed something they didn't believe: four out of every five salmon were wild.
Jim Johnson is a state fisheries biologist based in Alpena. He says, at first, they assumed there was some problem with the data. But in subsequent years they found the same results.
"It wasn't just a flash in the pan, it was a permanent change."
The change might sound like good news, more fish. But there were far too many. Pretty soon they ran out of food and died off. Today the once-famous salmon fishery in Lake Huron is pretty much gone.
Simply put, what happened in Huron was the fish adapted well to some rivers in Georgian Bay, at the far eastern end of the lake. Jim Johnson estimates that while the state was putting three million fish in the lake each year, as many as 14 million wild fish would be born in Georgian Bay. That overwhelmed the food supply of the whole lake.
Historically researchers have debated how much of a role zebra and quagga mussels played in the collapse of the fishery, but Johnson says he has come around to the view that it was mainly the over-abundance of salmon that caused it. You could say that the salmon, an exotic fish, became an invasive species in Lake Huron and wrecked the food web.
History catches up to Lake Michigan
Recently scientists have begun to talk about the fact that Lake Huron and Lake Michigan are connected by the Straits of Mackinac. They know fish pass through the Straits but have generally believed it's a minor factor. One scientist, however, has recently begun questioning that assumption.
Rick Clark retired from a career with the state and now does research through Michigan State University. Clark noticed something unusual about fishing in Lake Michigan during the past decade. He says the fishing was nearly as good as it was back in the 80s. That was the best fishing ever on Lake Michigan. But anglers spent about half as much time fishing in the 2000s and achieved the same results as they did back in the 80s.
"Which is hard to explain except that there must have been more fish out in the lake," he says.
Clark's hypothesis is that lots of fish have been coming over from Lake Huron. It's a just a hypothesis, but it's a troubling one. That's because if fish from Lake Huron are coming over to Lake Michigan, then what's to stop Lake Michigan from being overwhelmed by a legion of wild salmon from Georgian Bay? Clark says it is unlikely that Lake Michigan could withstand that kind of feeding pressure any better than Lake Huron did.
Assessing the threat
Rick Clark says he has been challenged less often than he would expect when he has presented his hypothesis to his colleagues. For him, and others, the question is how many fish are making this trip. But Mark Ebener says not many. He's a fisheries biologist for the Chippewa Ottawa Resource Authority who sees no reason to worry. Ebener says the salmon fishing is horrible in Lake Huron right now and that means there can't be too many fish breeding over in Georgian Bay.
"We would see substantially better fisheries in Lake Huron than what we see," says Ebener. "They're not going to make a beeline from Georgian Bay into Lake Michigan."
Ebener says it would take centuries for the salmon to develop such a specific migration pattern.
But the managers of Lake Michigan are anxious about this very possibility. And it is something of a wildcard as they decide how to maintain the state's prized salmon fishery. Another year and the issue should be much better understood, though. Every chinook salmon planted in the lake last year was tagged. And researchers will soon have a clearer picture of how the fish move around and where the wild ones are coming from.