|Guttenberg, Iowa — Kevin Hanson had to throttle back his heavy flat-bottomed aluminum boat as he began to break up a thin layer of ice that had formed overnight on the slack water in Pool 11 of the Upper Mississippi River.
Hanson, fisheries technician with the Iowa Department of Natural Resources (DNR) Guttenberg station, was on his last run of the year collecting traps for a mudpuppy population study before ice up.
Not much is known about the reclusive mudpuppy: it’s Iowa’s largest and only fully aquatic salamander; has distinctive red featherlike external gills; can live about 20 years in the wild; has poor eyesight; can grow up to 18 inches long or longer; and takes about 4-6 years to reach sexual maturity.
What is known is that mudpuppies are a threatened species in Iowa and serve as the host for the salamander mussel during its glochidia stage, the parasitic larval stage of mussels. It’s the only freshwater mussel without a fish species as a host and it is considered imperiled in much of its native range.
For salamander mussels to survive, they must be in close proximity to mudpuppies.
“That makes them pretty important,” Hanson said.
This population study began in 2015, but its origins reach back to the reclamation project from the 2008 Bluff Slough train derailment south of Guttenberg, when a dead juvenile mudpuppy was discovered during cleanup. A portion of the mitigation funds used to restore and restock a damaged mussel bed was set aside to survey the mudpuppy population.
“The data being collected will be added to what we know about them with the hope that it will begin to fill in the gaps with regards to growth and dispersal and reproduction,” said Katy Reeder with the Iowa DNR’s Wildlife Bureau. “It takes specialized surveys to find mudpuppies so we want to collect as much information as we can when we do find them.”
Hanson records the length, weight, gender, collects samples for genetic testing and swabs them for a virus study. Each mudpuppy receives a uniquely numbered Passive Integrated Transponder (PIT) tag as a parting gift so the data on things like growth rates and dispersal can be documented in the event these mudpuppies are recaptured.
Hanson set 15 traps between the four survey sites for two days before checking them. Each trap is baited with minnows and weighted in an attempt to hold their location on the river bottom. A few of these survey sites were found thanks to a local commercial fisherman who tipped Hanson off to where mudpuppies were showing up in his nets.
Hanson motors around slowly breaking up the ice to help locate the traps. Shifting the motor into neutral, he hooks the first trap and begins to pull up the line. After a minute, it appears at the surface with two mudpuppies – off to a good start. He’s had his best luck in water temperature below 60 degrees. The traps are emptied into a holding tank and the process is repeated with the remaining traps – three total at this site. Once all the traps are collected, Hanson beaches the boat and the work begins.
He’s developed his own method and tools to aid in the data collection. A clear plexiglass tank to check gender, a clear tube with a clear ruler glued to the bottom to measure overall length and snout to vent length. He takes photos of each mudpuppy recording their unique spotting pattern and connects the photos with the PIT tag number.
All the specimen handing and data collection is done on the water to minimize their time away from the river. Once the workup is done, Hanson releases them where they were caught. Including those caught on this early December day, Hanson has tagged 175 individual mudpuppies and recaptured 50, some more than once.
“We’re seeing reproduction in Bluff Slough, which is good,” Hanson said.
For five years, Hanson has spent a portion of his late fall days trying to catch this secretive and vulnerable salamander and during that time his respect for them has grown. “They’re just an amazing animal to work with,” he said.
Hanson has been collecting and submitting genetic material as part of a larger study by Eastern Michigan University on mudpuppy genetics across the Midwest that is already generating interesting results.
“The majority of the samples match the Minnesota genotype, but there was some genotype specific to the Mississippi River on both the Iowa and Wisconsin side,” he said.
There is also an east-west genetic divide, with mudpuppies from Iowa, Wisconsin, Minnesota and parts of Illinois different than those from the eastern states. While Iowa is on the western edge of their range, mudpuppies have been documented in the Des Moines River and the Upper Iowa River.
The Iowa DNR is involved with a separate study looking for mudpuppies in the Upper Cedar River from the Minnesota state line to the dam in Nashua.
The Upper Cedar River study is part of a joint Iowa and Minnesota Departments of Natural Resources effort to restore native mussel communities in the upper reaches of the Cedar River, through a competitive “State Wildlife Grant” from the U.S. Fish and Wildlife Service.
The purpose of this project is to propagate, rear, and reintroduce native mussel species into historically occupied habitats the Cedar River watershed where they have been lost.
“This section of the Upper Cedar River has habitat characteristics and water quality favorable for the salamander mussel but it would need its host species – mudpuppies – in order to survive,” Reeder said.
To date, Hanson has not found any mudpuppies from his surveys on the Upper Cedar River.
The project began in 2017 and Reeder is hoping to extend it to 2021.