GLADWIN – Why should residents of Gladwin County be concerned about Asian Carp, specifically Bighead, Silver and Black Carp? Most of us are well aware of several invasive species that have made their way into our area. The zebra mussel infests many local lakes and the Asian ash borer has decimated many local woodlots. Both species were introduced elsewhere, but eventually made it to mid Michigan. Can invasive carp do the same?

The recent eDNA survey of multiple inland lakes indicated the presence of carp DNA in three Michigan locations including Houghton Lake in Roscommon County. All three lakes have a high transient boater population, which may help explain the presences of the eDNA. All three lakes are miles away from any known established population of invasive carp. Lucas Nathan, Ph.D. Aquatic Invasive Species Coordinator for the Michigan Department of Natural Resources (MDNR) Fisheries Division participated in the follow-up survey and in a conversation last week offered the most likely explanation for the positive initial result.

He explained that the initial survey led by Michigan State University used a technique that allows for the “quantification of any eDNA “present in a body of water. It is a “broadcast approach” all of the eDna present (fish, invertebrates, plants) can be detected in a single subset of water samples. This technique is very sensitive and is used in the initial sampling to indicate bodies of water that may need further study. 

The follow up testing used a different technique that looks for “specific markers” found only in the species sought. Nathan said that the test indicated a “very low likelihood” that live individual carp were present. Good news of course, but it brings into question the source of the original eDNA. He mentioned that the most likely source was contaminated boats and fishing equipment. 

Silver and Bighead carp could “survive and thrive” in inland lakes according to Tammy Newcomb, Ph.D. Senior Water Policy Advisor for the MDNR. To colonize the lake they would have to have rivers of suitable size to spawn. At this time there are no known colonies in Michigan inland lakes. The biggest current threat is to Lake Michigan and Lake Erie.

Lake Erie is an ideal setting for invasive carp. It is warm and shallow with a lot of phytoplankton. Both Bighead and silver carp are filter feeders. They swim with their mouths open taking in whatever they come in contact with including juvenile fish. “Saginaw Bay would also be a great location,” according to Newcomb. “As would any of the drowned river mouths on Lake Michigan.”

It was originally hoped that Lake Michigan would prove to be too cold and deep to support Asian carp. “They have been found in very cold places elsewhere in the world,” said Newcomb. “The perception that our waters are too cold is false.” She also mentioned that the only limiting factor is “food.” Water depth is not a deterrent. They will go anywhere there is food. In explaining their adaptability Newcomb said, “they eat like alewives, spawn like walleye, and grow and swim like salmon.” There are no limiting factors in the Great Lakes. “They have been able to colonize everywhere they go.”

The key to protecting the Great Lakes and by extension our local inland lakes is to prevent these invasive fish from entering. Once they enter a body of water they are able to outcompete the native organisms. Bighead and silver carp are planktivores. They suck up the food found necessary for juvenile fish and native invertebrates such as mussels. They also eat larval fish. They effectively disrupt the entire food web. Newcomb mentioned, “predators are not effective because you can’t get them to a high enough density to have an effect. The carp also grow so fast that within a year they outgrow the mouth size of most fish that would feed on them.”

The most likely avenue for an invasion are the waterways in the Chicago area that connect the Mississippi River to Lake Michigan. Right now we are relying on an electric barrier to stop the fish. Newcomb says that these types of barriers are “not infallible.” As barges move through the barrier they create a shadow effect that sucks up the electricity needed to stop the fish. The carp can also get into the spaces between barges and move through with them. 

A more sophisticated barrier is planned for the Brandon Road Locks area. This barrier will include electricity along with a flushing lock and a structured channel. The structured channel will be a confined space that will also include an acoustic deterrent. Hopefully it’s not too late. Invasive fish have been found below Brandon Road.

Another area of concern is in Indiana and Ohio. Newcomb said that 18 different places were identified where their potential hydrologic headwater connection could be made between the Mississippi River watershed, Ohio River watershed and the Great Lakes. Most of those possible connections have been closed off. Three remain in Ohio, but the risk is very low. It would take extreme effort by the carp during times of massive flooding for them to move into the Lake Erie watershed.

Since control is virtually impossible once the carp get into a lake it is extremely important that fishermen do not inadvertently aid in their spread. The MDNR suggests that the best way for fishermen to help is to learn how to identify the fish especially the juveniles. It is illegal in Michigan to transport or possess live Bighead, Silver, Black and Grass carp. If found or caught, they should not be released. Baitfish should always be disposed of in the trash. The MDNR also asks that you report any suspected Asian carp. If you catch one do not release it.

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