Bighead and silver carp are making most of the news these days, as they threaten invasion of both the Great Lakes and inland fisheries in the Upper Midwest.
But before these two Asian carp species escaped from fish farms and began to devastate our rivers, a few states were trying grass carp --- yet another Asian carp species --- to manage invasive aquatic vegetation, notably hydrilla. And biologists developed a sterile (triploid) variety to lessen the likelihood that this exotic would reproduce in waters where it was introduced --- or to which it escaped.
For resource managers, the problem is that using these grass grazers for vegetation control is mostly an all-or-nothing proposition: Too much vegetation without them, none with them.
And the problem for the rest of us is that --- as with bighead and silver carp --- our elected officials bowed to special interests and failed to protect our aquatic resources. Grass carp always have been and continue to be much too easy to obtain.
As a consequence, illegal stockings are common, as has happened at the little lake behind my house. Grass carp now make up most of the biomass in the lake, meaning they basically have destroyed the sport fishery.
Fortunately, most grass carp sold today are sterile. But not all.
A grass carp recently shot by a bow angler in Michigan’s St. Joseph River was reproductively viable, according to the Michigan Department of Natural Resources (DNR).
What makes this especially disturbing is that the fish was in the Berrien County portion of the river ---- very near Lake Michigan.
DNR says this:
Grass carp are rarely found in Michigan waters. Previous cases were usually the result of illegal stocking in ponds or movement from other states where stocking genetically altered triploid fish for aquatic vegetation control is allowed.
Other states allow the stocking of triploid fish because they believe the fish have a low probability of reproduction, but the sterilization process is not 100 percent effective.
Given their potential negative effects on fish habitat, the DNR strongly opposes the use of triploid fish and reminds the public that live grass carp are illegal to possess, transport or stock in both public and private waters.
In response to this finding, the DNR’s Fisheries Division will continue to assess the distribution of grass carp in the lower St. Joseph River through electrofishing surveys this fall, monitoring movement through fish ladders and angler harvest reports. Potential points of entry will also be assessed to prevent further releases in Michigan waters.