Michigan Trout Unlimited
MICHIGAN Trout
Aquatic Invasive Species & Trout Streams: It’s Up to All of Us Now
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by Dr. Bryan Burroughs, Michigan TU Executive Director
Spring 2022
The Great Lakes have been plagued and transformed by aquatic invasive species (AIS) over the last 20-60 years: first by sea lamprey and alewife, and later by dreissenid mussels and gobies, among many others. Not every new invader finds a competitive niche and explodes, but every so often, a new AIS does with transformative impacts to our waters. Over the years, we’ve seen a few of these show up in our trout streams. Sea lamprey spawn in streams, and juveniles are raised there for several years, living in soft sediment bottom areas. Fish passage barriers and chemical treatments are employed to address the sea lamprey, often with costs to the health of coldwater fisheries in those streams. Zebra mussels have been transported into some of the reservoirs on trout streams and seem to find suitable conditions downstream of the dams. Gobies are present in many streams but, thankfully, don’t seem to thrive in healthy, intact, well-functioning coldwater stream systems. Over the last five years, we’ve seen some new AIS appearing in trout streams, and these more recent invaders seem particularly suited to the conditions. New Zealand mudsnails (NZMS) were first detected in the Pere Marquette River around the flies-only waters and subsequently in other river sections. Shortly afterward, they were seen in portions of the Au Sable and Boardman Rivers, more recently in the Upper Manistee River, and this past year in the Grass River where Shanty Creek joins it. Didymo, or “rock snot,” primarily found in the St. Mary’s River rapids, was discovered in the Upper Manistee River around Christmas 2021. These species appear well adapted to flourishing in trout stream conditions and have exploded to incredible abundances in other places. Now that they have been introduced to these rivers, only time will tell how prolific they become and how great their impact on the fisheries. Currently, there are no well-developed treatments for eradication. It is difficult to determine with certainty how these AIS were introduced into these streams. Adult NZMS can be no larger than a grain of rice, and didymo, a diatom, is far more challenging to detect. In the future, it may be possible with genetic tools to understand how these AIS found in Michigan rivers are related and to perhaps piece together a picture of where they came from and how they spread. But, for now, anglers are a major vector for spreading these AIS into streams. Regardless of where they came from initially, they are here now, and all of us are the most likely means by which they will continue to spread to new trout streams.
We must all accept the responsibility for preventing their spread. Contemplate for a moment how many anglers have enjoyed our incredible trout fisheries before us; how much effort has gone into repairing and protecting these fisheries so that they continue to be vibrant, amazing angling destinations; and how many future anglers deserve the privilege of enjoying what we have been able to. We find ourselves in a situation where simply moving between two rivers can jeopardize all that. We all must adapt routines to decontaminate our fishing gear and do so as a habit. Do you share your toothbrush with others? Do you serve food on dirty plates without washing them? We find ourselves with clear and present threats to the future of our trout streams, and we can no
