The potential for Asian carp getting into the Great Lakes from the Illinois River has grabbed most headlines on invasive species and their threat to the fishing industry along Michigan's waterways.
But in the Port Huron area along the lower Lake Huron and the St. Clair River, the dreaded carp are not among the exotic organisms that are raising red flags right now.
Great Lakes worries
Thankfully, Asian carp--a blanket term used to refer to four varieties of carp, with bighead and silver carp being the species to watch for on Michigan waterways--haven't penetrated into the Great Lakes yet.
Although those fish are a big issue on the Illinois River near Chicago, electrical barriers and removal programs aimed at keeping them from moving upstream into Lake Michigan have so far been successful keeping them at bay. These carps are a fast-growing, adaptable species, so the big concern is that they'll outcompete and crowd out other species in our state's waterways, crippling the sports fishing industry.
Seth Herbst is an aquatic invasive species coordinator for the Michigan DNR's Fisheries Division. He tells
The Keel his agency and the U.S. Fish and Wildlife Service have an early detection program that monitors the environment for the carp's DNA.
"Fortunately all those samples, and we're talking thousands of samples over years, have come back negative," he says. "So that's encouraging and provides us with a lot of evidence that bighead and silver carp are not in Michigan waters."
There isn't much in the way of commercial fishing along southern Lake Huron--and what's there is limited to smaller operations using trap nets--but sports fishing is a big industry on both the lake and the St. Clair River. The area is renowned for its amazing walleye fishery, and species like sturgeon and catfish also draw anglers to local waterways in droves.
If you ask Bob Jury, an avid fisherman who works at Bob's Pro Bait in Port Huron, he'll tell you that although the fishing's been good lately, the salmon population has seen better days.
"The salmon crashed here about 10-11 years ago," he says. "Guys are kind of adapting to salmon not being here. [They're] lake trout fishing now...Lake trout have really taken over Lake Huron here."
A recent U-M study
found Lake Huron's Chinook salmon population, in particular, has collapsed in recent years; the report urged those who manage the area's waterways to concentrate their energies on fostering native fish species such as lake trout, walleye, lake whitefish and lake herring.
So what explains this drastic decline in the area's salmon? It's linked to a disruption of the local aquatic food web that's intimately tied to a proliferation of invasive species.
A tangled food web
To start with, alewife, a non-native prey fish that for many years served as a main food source for salmons and other predators, has virtually disappeared.
According to the previously mentioned U-M study, between 2002 and 2003 the biomass (total combined weight) of alewives in Lake Huron plunged by more than 90 percent.
The plight of the alewife stems from the appearance of zebra and quagga mussels, tiny aquatic mollusks that arrived here in the 1980s. The mussels entered the waterway through the ballast water of international shipping vessels and quickly proliferated. Due to their incredible ability to consume zooplankton and phytoplankton, which form the base of the lake's aquatic food web, the mussels have greatly reduced food availability for smaller prey fish like alewives.
"Once alewife took that huge dive, the chinook salmon and a lot of the other species that were very reliant on alewife for food no longer had a food source, so their populations declined rapidly," says Herbst.
He says other predator species like brown trout, lake trout and walleye have also been affected.
Currently quaggas seem to be replacing zebras as the dominant mussel in the area. Mussels, however, aren't the only non-native species causing distress along Lake Huron and the St. Clair River.
New and old invaders
Sea lampreys, a parasitic fish with a ringed mouth and tooth-capped tongue that feeds off the vital fluids of other fish, arrived in the area in the 1950s from the Atlantic Ocean and continue to be a problem.
"U.S. Fish and Wildlife Service sampling has shown the St. Clair River to be a large producer of sea lamprey, which is thought to be responsible for increased wounding rates on native fish in Lake Erie," says DNR fisheries research manager Todd Wills.
Another issue are round gobies, though they are more of a mixed bag than some other species. They eat zebra mussels and serve as a source of prey for larger fish, but also feast on fish eggs and are linked to increased rates of botulism in birds. Anecdotally, Wills says the goby population appears to be down at the moment. But many sport fish species, including smallmouth bass, yellow perch, brown trout and lake trout feed on round gobies.
And although there have been three recent reports of red-bellied pacu
, a piranha-looking fish with human-like teeth, in local waters, the DNR doesn't currently view them as a concern as the tropical fish are unlikely to survive Michigan's harsh winter. The agency is, however, concerned about the dumping of pet fish into local waters, which is how they think the pacu got introduced here.
Another problematic species is the spiny water flea, a tiny organism that's classified as a zooplankton. As its name suggests, water fleas have a prominent spine, but they have little nutritional value to the young fish that consume them, and can cause health issues.
Aquatic invasive plants are also causing problems in places; by reducing habitat for fish and clogging up the motors of passing boats. Eurasian watermilfoil, which outcompetes local water flora and grows in thick patches, is a particular nuisance. Water lettuce, water hyacinth and european frog-bit cause issues by forming dense clusters near the surface of the water. The DNR urges aquarium owners not to dump their water gardens into local waterways, as doing so can exacerbate these kinds of issues.
The good news
Despite the presence of all these invasive species, though, Bob Jury says there's plenty for local fishermen to be happy about, as this season has been one of the best in recent memory.
"This has probably been the best year for walleye in this area in 10 years," he says. "It's been going on for three months straight out in the boats. The sky's the limit for fish!"
This story is a part of a statewide Invasive Species Community Impact Series. Support for this series is provided by the Michigan Department of Natural Resources.