The Detroit River in the winter can be an inhospitable place. The temperatures dip into the teens, and the wind whips large plumes of snow from the tips of frozen waves. This large and fairly fast-moving river flows south and southwest, connecting Lake St. Clair and Lake Erie. The river plays an important role as a shipping channel for freighters carrying industrial compounds and other materials used for manufacturing. 

Underneath all of this ice and hustle and bustle, one of the river’s most curious and secretive animals is carrying about its business, breathing with large, bushy external gills, foraging along the rocky bottom for food and undergoing mysterious mating behaviors. This animal is known as the northern mudpuppy (necturus maculosus maculosus), and the frozen and harsh conditions of the Detroit River are just what it’s been waiting for all summer long. 

Mudpuppies are amphibians who inhabit lakes, streams and rivers all throughout the U.S. Midwest and into parts of Canada. It is a type of fully-aquatic salamander that utilizes external gills, which are flush with blood and used to extract oxygen from its aquatic environment. Its tail is large and paddle like, and its skin is covered in a thick layer of slime. These salamanders, like all amphibians, have permeable skin and are considered to be a good indicator of environmental quality. This is one of the reasons the Detroit Zoological Society (DZS) began tracking the health and abundance of mudpuppies back in 2009.

In 2016, the Michigan Department of Natural Resources elevated the conservation status of the northern mudpuppy to a species of special concern. Since that time, the project has continued and expanded, focusing primarily on Belle Isle Park in the city of Detroit. The Detroit Zoo utilizes minnow traps to capture the mudpuppies without harming them while still collecting important data. The traps are baited with smelt and catfish bait to lure these aquatic salamanders into the minnow traps. The traps are set on the first day of the survey and pulled in on day two, so that the animals spend the least amount of time possible inside.  If a mudpuppy is found inside, DZS staff proceeds to gather data and observations about the animal, including size, weight and gender. The gills are checked for health and examined for parasites. The digits on all the limbs are checked for malformations, which could indicate the potential presence of pollutants in the river. 

Once these measurements are taken, the animal is tagged with a Passive Integrated Transponder tag, which is injected into the base of the tail. This transponder can be scanned if the animal is captured again. Additionally, it tells DZS researchers useful information that can be used for future data analysis. In addition to these measurements, data is collected on water quality and additional environmental conditions, such as temperature and dissolved oxygen content. 

Based off the data so far, most mudpuppies are caught in late fall or early winter. During this time, male mudpuppies are pursuing females in the quickly cooling shallow water close to the island. Many times, staff has observed male and female mudpuppies in the same trap this time of year, most likely with the female entering the trap first before the eager male mudpuppy follows her inside. Once mudpuppies have successfully bred, the females deposit their eggs in spring, and within a month or two, the eggs hatch into several hundred baby mudpuppies!

All of this drama is taking place out on the frozen Detroit River. With ice floats and enormous boats hovering overhead, these specialized amphibians continue to live and breed intertwined in an urban environmental landscape that still holds many secrets yet to be revealed.

– Mark Vassallo is an amphibian department supervisor for the Detroit Zoological Society.