The latest round of eDNA testing for Asian carp in the Mississippi River has yielded unexpected results, according to the Minnesota Department of Natural Resources (DNR).
Nineteen of the 48 water tests near the Coon Rapids Dam have tested positive for silver carp DNA, and three of the positive results are from above the dam. The highly sensitive tests are designed to detect DNA in the environment that comes from the mucus or excrement of invasive Asian carp. Although testing was done to detect DNA of two Asian carp species – bighead and silver – all positive results were for the leaping silver carp.
The Coon Rapids Dam, located upstream of the river’s lock and dam system, has been a significant fish barrier since it was upgraded in the 1970s, preventing a number of native species such as white bass from migrating upstream. DNR fisheries biologists are surprised by the positive eDNA results.
“We are investigating the likelihood of false positives or other sources of Asian carp DNA in the river,” said Tim Schlagenhaft, Mississippi River manager for the DNR. “A study being done in the Chicago area is providing insight into other potential sources of Asian carp DNA, where they have also been getting positive eDNA samples but have been unable to document the presence of live fish. The results of that study will help determine other potential sources of DNA in our waters. Until we can prove the DNA is from other sources, the risk is too high to assume live fish are not present.”
In recent years, the dam’s effectiveness as a fish barrier has figured prominently in the DNR’s strategy for keeping invasive Asian carp out of the Mississippi River north of the Twin Cities. The dam is about to undergo $16 million in repairs and upgrades in an effort to further improve its effectiveness as an Asian carp barrier. DNR officials said the improvements are still necessary to slow the upstream spread of Asian carp in the Mississippi River.
“The positive test results don’t change the fundamental goal of the state’s Asian carp action plan,” said DNR Commissioner Tom Landwehr. “We must research and implement our available options to prevent or slow the movement of Asian carp upstream in our river systems, and to manage and control their populations should they become established.”
So far, most of the eDNA tests done on Twin Cities metro area rivers have come back positive for silver carp, but extensive netting efforts in the St. Croix and other parts of the Mississippi River this summer and fall have not yielded any of the elusive fish.
The netting results and ongoing commercial fishing in the Mississippi River further downstream suggest a very low population of invasive carp, said Schlagenhaft, so there is still time to implement strategies to slow their movements and keep population levels low.
Gov. Mark Dayton will hold his third Asian Carp summit Dec. 20 to discuss the state’s proposed actions on Asian carp.
The eDNA testing has been conducted by the Asian Carp Task Force, a consortium of local, state and federal agencies, along with local environmental groups, examining Asian carp risks and policies. When eDNA is detected, the group’s protocol is to deploy netting operations to look for Asian carp.
The DNR said it will hire a commercial fisherman to look for Asian carp below and above Coon Rapids Dam, as it has at other sites where the carp DNA has been detected.
The eDNA samples were collected last September. Test results are still pending for water samples collected in the Minnesota River and above the St. Croix Falls Dam on the St. Croix River.
Here are the test results for the St. Croix River and various sites on the Mississippi River. All positives were for Silver carp, there were no Bighead carp samples testing positive:
• St. Croix River below St. Croix Falls – 22 out of 50 samples.
• Mississippi River below Ford Dam – 14 out of 52 samples.
• Mississippi River below Hastings Dam – 19 out of 62 samples.
• Mississippi River above Coon Rapids dam – 3 out of 19 samples.
• Mississippi River below the Coon Rapids dam – 16 out of 29 samples.
Bighead and silver carp are voracious eaters, capable of eating 5 to 20 percent of their body weight each day. Asian carp feed on algae and other microscopic organisms, often outcompeting for food with native fish. Scientists believe the fish could severely disrupt the aquatic ecosystems of Minnesota waters.
Read more about Asian carp.