This tiny crustacean is a favorite food item for Great Lakes fish. Scientists are trying to figure out why it's disappearing. (Photo courtesy of the Great Lakes Environmental Research Lab)
One of the basic building blocks of the Great Lakes food chain is disappearing. The bottom of the lakes used to be teeming with tiny crustaceans known as Diporeia. But their numbers are declining, and in wide stretches they’re just simply gone. Commercial fishers are beginning to see the effect on fish. The Great Lakes Radio Consortium’s Lester Graham has an update:
Transcript
One of the basic building blocks of the Great Lakes food chain is disappearing. The bottom of the lakes used to be teeming with tiny crustaceans known as Diporeia. But their numbers are declining, and in wide stretches they’re just simply gone. Commercial fishers are beginning to see the effect on fish. The Great Lakes Radio Consortium’s Lester Graham has an update:
Diporeia is a quarter-inch long shrimp-like creature that
lives in the sediment at the bottom of most of the Great
Lakes. Just about every fish at some time in its life
relies on diporeia for food. Those that don’t, eat the
fish that eat diporeia. Researchers used to find 10,000
of these animals in a square yard of sediment. Today the researchers are disturbed because they’re
taking up samples and finding only hundreds in a square yard and
sometimes finding none, not one.
But this isn’t simply scientific curiosity for
biologists. It has economic impact. Mark Gaden is with the
Great Lakes Fisheries Commission. He says this is
beginning to affect commercially harvested fish.
“There’s a very deep concern about the impact of
the loss of diporeia on the white fish diet.”
Gaden says the commercial fishers starting noticing that
the white fish looked different. Their body weight just
wasn’t what they were used to seeing.
Tom Spaulding is one of the partners in Gauthier &
Spaulding Fisheries in Michigan. They fish on Lake Huron.
He says white fish there aren’t getting enough to eat.
“Well, some of them definitely look skinny alright. And the other ones, they’re a longer fish, but
they just don’t have the body weight they should for a fish
that length. So, it’s got to be food-related, their
natural food, that diporeia shrimp. You see what I mean?”
And it’s not just the commercial fishers on Lake Huron.
It’s happening everywhere except Lake Superior. The Great
Lakes Fisheries Commission’s Mark Gaden says it’s got a lot
of fishers worried.
“Anytime, though, where you have something like
diporeia which is something that’s critical in the food web
and you see drastic, drastic declines in it and we’re not
quite sure why this is taking place, it’s cause for serious
concern.”
The commercial fishing industry is looking to the
researchers. The researchers have been working on this
problem for years. So, what’s causing it?
“Well, that’s what I’m struggling with. There’s
a lot of conflicting evidence.”
Tom Nalepa is a research biologist at the Great Lakes
Environmental Research Lab. He says it’s possible that the
invasive species the zebra mussel might be eating most of
the diporeia’s food.
“It lives on the bottom, but it needs that fresh
material that drops down right at the sediment surface.
And, this is exactly the same materials that zebra mussels
are filtering out. So, logically, it’s a food problem, but
the confusing thing about it is that the animals are not
showing any signs of starvation. They’re relatively
healthy, yet the population is dying off down to zero.”
The researchers continue to try to figure out exactly
what’s going on. But, if the zebra mussel is the culprit
in the die-off of the diporeia, the scientists say there’s
nothing that can be done about it. It’ll mean a huge
change in the natural balance of the Great Lakes. The
commercial fishers such as Tom Spaulding say they’re
hopeful that the white fish will find something else to eat.
They hope it’s just a matter of time. But, in the
Meanwhile, Spaulding says it’s not just white fish that are
being affected. It’s the fish that sport fishers like to
catch too.
“We’re seeing skinny lake trout out there.
We’re seeing other species too that are suffering because
the food chain, the food they’re after is low. But, it’s
not just a white fish problem in the Great Lakes right
now. And the finger seems to be pointing to the zebra
mussel, so, it’s a serious problem as far as changing the
whole ecosystem out there that we see.”
This might be only the latest economic damage caused by the
zebra mussel since it stowed away in a cargo ship in the
early 1980s. The mussel has cost industry because it clogs
intake pipes. It’s damaged the native mussel populations.
And the long-term damage to the environment of the Great
Lakes and the Mississippi River system where it’s also
spread is not yet clear.
One thing is clear – Any savings realized because of those cheap goods on that cargo ship,
can’t possibly offset the cost to the economy because of the zebra mussels that ship carried in its
ballast water.
For the Great Lakes Radio Consortium, this is Lester Graham.