Survey reveals more Asian carp in Marrs

Harsens Island, Mich. — Fisheries biologists’ fears turned to reality recently when more Asian grass carp were found in Lenawee County’s Marrs Lake.

On May 16, the DNR received anonymous photos alleging the presence of Asian grass carp in the 39-acre lake.

After interviewing lake residents and gathering more anecdotal evidence, fisheries biologists surveyed the lake in June and caught a 25-pound, 37-inch diploid (capable of reproducing) Asian grass carp.

“The crews were … successful in the capture of one grass carp. While electro-shocking, three additional grass carp were seen, but were not able to be netted,” DNR Fisheries Division Chief Jim Dexter wrote in a memo presented to the Natural Resources Commission last week at its monthly meeting, held on Harsens Island.

Grass carp, like bighead and silver carp, are illegal to possess, sell, or stock live in Michigan.  They do not pose the same risk as bighead or silver carp, but  possession of live grass carp is outlawed because they eat beneficial types of aquatic plants and alter fish habitat. 

Grass carp have been found in Michigan waters in light numbers for more than 30 years, but there has been no indication they are reproducing. Officials believe they entered the state through illegal stocking in ponds and lakes, or movement from other states where the genetically altered triploid (sterile) fish are used to control weeds. Some states, including Ohio, allow the stocking of triploid fish because they believe there’s a low probability of reproduction; however, the sterilization process is not 100-percent effective.

Samples of the captured carp were sent to two labs to determine if the fist was a triploid. Both results revealed that the fish was a diploid, capable of reproducing, and it had developing egg sacs.

“Now that the fish is confirmed to be a diploid and capable of reproduction, we need to do additional work to remove the remaining grass carp and assess if there are any others present and if they may have been reproducing,” Dexter wrote. “But young carp are notoriously difficult to collect.”

To date, three Asian grass carp have been removed from Marrs Lake – the one the DNR collected; one that was caught by an angler, a picture of which was sent to the DNR in May; and a 58-pounder that was shot by a bowfisher.

Since Marrs Lake is connected to other lakes in the area, biologists will take e-DNA samples from those lakes to determine if they are infested with grass carp. Fisheries Division personnel will continue with manual removal efforts and continue evaluation  of the lakes to determine how big the problem is.

“As we continue to work on this issue, we will be developing a strategy to effectively deal with any population of carp thay may be present in Marrs Lake or any of the other potentially connected lakes,” Dexter wrote. “We are hopeful that we are only dealing with a few fish.”

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