Scientists have confirmed for the first time that a species of the dreaded Asian carp has reproduced naturally in a Great Lakes tributary.
While not the variety of Asian carp experts fear will do the most harm in the Great Lakes region, the results have important implications for those concerned about the spread of this invasive species.
Four grass carp, a species of Asian carp, were caught by a commercial fisherman last year in the Sandusky River and analyzed by U.S. Geological Survey (USGS) scientists. They determined that the invasive fish were at least one year in age and had the capacity to become spawning adults.
Researchers used a method of studying bones, known as otoliths, in the heads of the fish to determine that all four fish had lived in the Sandusky River watershed for their entire lives, according to the results of a USGS study released Monday and published in the Journal of Great Lakes Research.
“The Sandusky River has unique chemistry due mainly to the geology of the area. It allows us to determine if a fish has spent all or part of its life there,” said Duane Chapman, Asian carp research leader at the USGS Columbia Environmental Research Center.
Naturally occurring levels of strontium, a chemical element with similar properties as calcium, is taken up by the fish and becomes incorporated into its bones. Strontium is found nowhere else in the Great Lakes region or eastern U.S., so it creates a unique signature in the otolith bone, in particular.
“Successful reproduction of grass carp in the Great Lakes is an indication that other species of Asian carp—silver, bighead, and black carp—might be able to reproduce there,” according to a USGS statement. Researchers had previously believed that Asian carp required bigger rivers than the 14-mile long Sandusky to find suitable habitat for spawning.
“These findings are significant because they confirm recent USGS research indicating that shorter rivers, like the Sandusky, are potential spawning sites for grass carp and other Asian carps as well,” said Chapman.
Silver and bighead carp are the varieties of Asian carp that experts worry most about. They have a voracious appetite for algae and other microscopic organisms, which puts them in direct competition with native fish. Silver and bighead carp escaped from aquaculture ponds in the 1970s and spread northward, overwhelming the Mississippi and Illinois River systems.
Unlike the other two species, which are filter feeders, grass carp are a concern because they eat rooted aquatic vegetation, or macrophytes. Large North American rivers don’t have a lot of this kind of vegetation, so this is why they are not more widespread in the Mississippi River system Chapman says.
Unfortunately, where this kind of vegetation does grow – near the shorelines of lakes and in wetlands – grass carp could nearly eliminate the plants that provide important food and habitat for fish, ducks, and other aquatic species in the Great Lakes ecosystem. These same plants also help prevent shoreline erosion and take up nutrients that might otherwise trigger algae blooms, including problematic cyanobacteria blooms.
New Tools and Techniques Help with Early Detection
As the map shows, grass carp have been found in the Great Lakes watershed before, and in fact, another half dozen have been caught this year in Ohio waters alone, Chapman says. They are still considered uncommon, and until now, all previous catches were confirmed or assumed to be sterile, mainly because researchers lacked a reliable method for determining otherwise.
In the past two years, scientists developed a break-through technique for determining whether grass carp are fertile or not. This test usually requires a blood sample from the fish, but by the time researchers receive a fish to sample, it’s dead or frozen. USGS researcher Jill Jenkins found a way to test fertility by using the eyeballs, which usually arrive to the lab intact.
Until this year, about 20 rivers were thought to have potential spawning habitat for Asian carp, but newer models predicted that rivers like the Sandusky could provide suitable spawning habitat. The results of the current study verify this model.
“The model provides us with a valuable tool because we can take another look at the rivers in the Great Lakes basin and determine if there are any others that we should be concerned about,” Chapman said. “We haven’t done this yet but need to because these are the places we should be monitoring for silver and bighead carp as part of an early warning system.”
The techniques used in this study, along with studies of Asian carp DNA in the Great Lakes region, contribute greatly to the early detection of the species.
The Fight to Prevent or Slow Invasive Asian Carp Continues
These latest findings come at a time when the U.S. government has invested nearly $200 million on Asian carp prevention and control as part of the Great Lakes Restoration Initiative, including the installation of a new electric barrier and implementation of other measures to block the passage of Asian carp from infested waters of the Mississippi River to Lake Michigan through the Chicago Sanitary and Ship Canal.
The good news is that no Asian carp have been captured or observed above the existing barriers in the last two years, according to a statement earlier this year by the U.S. Army Corps of Engineers.
All options to prevent or slow an invasion are being explored. And at the very least, buying time is considered a good thing.
“Just look at the millions of dollars spent on sea lamprey control every year. Once the invasive species is established, the costs are never-ending,” International Joint Commission scientist and board secretary Mark Burrows said in a conversation earlier this year. He was making the point that if an aquatic species invasion can’t be prevented, the next best option is to delay the inevitable as long as possible.
Burrows explained that a targeted biocide has now been developed to control zebra mussels. “Imagine if we had something like that available thirty years ago.”
“People are smarter than fish,” said Chapman. “We know so much more about Asian carp than we did even ten years ago.” He’s banking on human ingenuity to help prevent the establishment of the nuisance species in the Great Lakes ecosystem, or as a last resort, to keep them from causing too much harm if they do become established. “We’re making great progress, but we’re not there yet,” he said.
Because of the potential consequences of an Asian carp invasion, boaters, fisherman and others who enjoy the Great Lakes waterways are advised to take extra precautions. Sterile grass carp are legal in some areas, so fishers are asked to be careful to buy fish and bait from a reputable outlet. “If you raise your own bait, use it in the same place,” advised Chapman.
Cleaning boats and not carrying water or bait between different water bodies can help prevent the spread of Asian carp and other invasive species. Supporting research and investments in prevention measures in the Chicago-area waterways and elsewhere is another way to help avert an invasion.
This latest news from Ohio is no reason to give up the fight just yet.
January 7, 2014 update: The Great Lakes and Mississippi River Interbasin Study is now available. The Alliance for the Great Lakes is encouraging people to make their voices heard on the issue of Asian Carp in upcoming public meetings and by sending comments to the U.S. Army Corps of Engineers.
Lisa Borre is a lake conservationist, freelance writer, and avid sailor. With her husband, she co-founded LakeNet, a world lakes network, and co-wrote a sailing guide called “The Black Sea” based on their voyage around the sea in 2010. A native of the Great Lakes region, she served as coordinator of the Lake Champlain Basin Program in the 1990s. She is now an active member of the Global Lake Ecological Observatory Network.