While working with his colleagues Wes Sleeper and Mark Hempel, Kramer pulled in a net to find he had caught the blue crab.
"Part of the exciting aspect of river research is that when you use a type of gear, you never quite know what you'll get when you pull it back out of the water," Kramer said.
The group is working with the Missouri Department of Conservation as part of a statewide paddlefish project aimed at assessing the quality of Missouri's waters for sport fishing.
"You never know what you'll find unless you take a look and see for yourself," Nelson said. "I'm glad Nick's passion and education allowed him to be out on the river last week and pull that net and take a look."
According to Nelson, only one other blue crab has been caught this far north on the rivers in the Heartland. That happened in 2004 when a crustacean with a blue hue was taken off an intake screen of a power plant in the lower Ohio River near Metropolis, Ill.
It's not exactly clear how the crab ended up in the Mississippi River. According to Nelson, many aquatic species will swim on their own for hundreds of miles, while other go with the flow of wherever the water takes them.
Nelson does have his own theories.
"Sometimes people inadvertently transport hidden 'hitchhikers' on boats and other vehicles," Nelson said. "Other times people simply dump aquatic species into lakes or rivers out of convenience."
The surprise catch won't change the findings of the paddlefish study.
"It is, at this point, a rather interesting discovery, unexpected for the region, and a reason to stop and think about the best ways to protect our native species," Nelson said.
The catch lead to "amazing interest" in crabs as a delicacy, Nelson said.
For those looking for a crustacean to "dip in butter" there are 33 species of crayfish native to waters throughout Missouri, Nelson said.
A rare blue lobster was saved from the dinner table in 2014. The lobster came in a regular shipment from Massachusetts-based supplier North Atlantic to the Schnucks Market in Cape Girardeau. It was moved to The World Aquarium in St. Louis. The blue lobster is estimated at one out of every two million.
More information about fish populations and MDC fish research can be found at mdc.mo.gov.