The Invasion of the Quaggas

  • A close-up of the quagga mussel. Quaggas have spread in all of the Great Lakes except Lake Superior. (Photo courtesy of the Michigan Sea Grant Archives)

Whitefish is a main dish for everything from fish boils to fancy dinners all around the Great Lakes region. But in some areas of the Great Lakes, whitefish aren’t doing so well. Rebecca Williams reports on what’s happening to the fish many people love to eat:

Transcript

Whitefish is a main dish for everything from fish boils to fancy dinners all around the Great Lakes region. But in some areas of the Great Lakes, whitefish aren’t doing so well. Rebecca Williams reports on what’s happening to the fish many people love to eat:

(sound of knives getting sharpened and fish being filleted)

Mike Monahan sells fish from all over the world at his seafood market. But he says whitefish is a very popular seller.


“It’s been there forever, and everybody just expects it to be there, and it’s inexpensive. But really it’s a great fish, as far as a nice light delicate fish, I’d put it up against the soles and flounders.”


Monahan says he’s still getting good supplies of whitefish. So, for now, he’s happy.


But some of the people who catch whitefish are worried. Commercial fishers have been hauling in skinnier whitefish in some parts of the lakes. It’s taking whitefish longer to grow to a size worth selling. And in some cases, the fish aren’t fat enough to make a good fillet.


(sound of shorebirds)


Paul Jensen fishes for whitefish in Lake Michigan. He says lately, he’s had to move his boat to deeper waters. That’s because whitefish are hungry and they’re swimming out deeper. They aren’t finding their favorite food. It’s a little shrimp-like creature called Diporeia.


“Diporeia are probably like a Snickers bar to whitefish; they were high in fats, high in lipids and it was their main food – it was very nutritious for them and it affected their growth rate. Eating Diporeia a fish could reach maturity maybe in 18 months or 2 years. Now we’re looking at fish that may take 5 years to get there.”


Whitefish are not eating Diporeia because it’s vanishing. In some places, researchers used to find 10-thousand of the little critters in a square meter of sediment. Now there are very few, or none at all.


Tom Nalepa has been trying to figure out why. Nalepa is a biologist with the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Lab.


“It’s a real scientific puzzle as to why Diporeia is declining. It’s definitely related to the spread of quagga mussels and zebra mussels but that exact negative relationship is kind of elusive at this point in time.”


But Nalepa says he’s sure the invasive mussels are to blame. The mussels got into the Lakes in the ballast tanks of foreign ships. And they’ve spread in all the lakes except Superior.


Tom Nalepa says he’s seen populations of Diporeia crash right around the time the mussels were booming. Nalepa says now, Diporeia’s gone from large areas in most of the Lakes.


That’s bad because Diporeia is an important food source for most of the fish in the Great Lakes.


But for whitefish it’s really crucial. Back in the good old days, Diporeia made up about 80% of their diet.


Tom Nalepa says whitefish are trying to find something else to eat. He’s seeing them switch to a snack food that could make them even skinnier.


They’re starting to eat quagga mussels.


“When whitefish feed on quagga mussels they have to deal with the shell which has no energy content at all and it has to pass the shells through its digestive system so basically the fish feels full when it’s not getting any energy source.”


Nalepa says to the fish, quagga mussels must seem like good food, because there are lots of them.


He says quagga mussels are booming, because they can live in harsher conditions than zebra mussels can. So biologists are predicting quaggas will be even worse for the lakes than zebra mussels.


“Where are things ultimately going to end up? People may just have to get used to fewer fish. Because basically now we’re trading the fish community for the mussel community. The lakes are loaded with mussels instead of fish now. It may be just the way it’s gonna be.”


Some fishermen are already seeing things change. One day last season, Paul Jensen pulled in some of his nets. He was expecting fish.


“It was kind of startling because the amount of quagga mussels that came up with those nets far exceeded the catch of fish. And we hadn’t really equipped the boat with a snow shovel to shovel quagga mussels out of the boat. The impacts are startling because you begin to wonder, if our little net caught these, how many are there and what are the impacts going to be down the road?”


Jensen says he wishes the invaders had never gotten into the lakes in the first place, because there’s no way to predict what effect they’ll have next.


But some scientists worry these changes at the bottom of the food chain will lead to a major collapse of the fish stocks that many people depend on.


For the Environment Report, I’m Rebecca Williams.

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