Jeff Gunderson, Minnesota Sea Grant Program, 218-726-8715

Musky fishermen on Lake Vermillion pine for the “weed” beds that used to hold muskies, now gone because of hoards of plant-eating rusty crayfish. Some fishermen sing the praises of bass fishing along the edges of dense aquatic plant beds. Others recognize that many lakes’ fish populations have changed as aquatic plants have disappeared due to lakeshore development. What is the relationship between aquatic plants and fish populations? Sounds simple enough to answer until you sit down to consider the issue’s scope. There are so many species of plants and fish and variations in how they interact that it is an oversimplification to state that all fish depend on healthy native aquatic plant populations. Some fish species need aquatic plants sometime during their lives while others don’t.

I’ve spent most of my career focused on Great Lakes fishes. Many of those species don’t ever see a rooted aquatic plant and they do just fine, such as lake whitefish, lake trout, coaster brook trout, lake herring, deepwater chubs and sculpins. Other fish like largemouth bass thrive with more aquatic vegetation and have increased dramatically in some areas of the Great Lakes. Take Lake Erie for example – prior to the 1990s, poor water clarity in that very productive lake limited plant growth. But when the invasive zebra mussels and quagga mussels populations grew in the lake, they filtered the water and improved clarity to the point that aquatic plants began growing in areas that hadn’t seen them in close to 100 years. As a result, largemouth bass and sunfish increased in numbers and size in those areas where the plants began growing again.

What does this have to do with inland Minnesota? It reminds us that different fish species have different habitat requirements and that loss of critical habitat will result in loss of fish. As with Lake Erie, we may not know what we’re missing because the habitat has been altered for so long that we’ve forgotten how it was. Or a gradual decline in aquatic plant communities results in an almost imperceptible change in the fish community that is difficult to detect during a single generation. Changes may only become clear when you look through old photo albums at your cabin and realize your grandfather caught more of a particular fish species than you do.

One thing is sure – many fish species and other animals depend on healthy native aquatic plant communities for food, habitat, cover, and spawning or nesting sites. What we don’t know is how our individual actions add up to impact a lake. How many individual shoreland property owners (or rusty crayfish for that matter) each removing the aquatic plants on their shoreline does it take to change the lake’s habitat enough to impact its fish?

Without careful consideration about how our individual choices add up to impact lakes, pretty soon we are going to sound like our grandfathers talking about the good old days. New fishery management tools and regulations and the catch and release practices of many anglers, combined with taking care of fish habitat could help ensure that the good old days of fishing in Minnesota are still ahead of us.

Posted in Fish and Wildlife, Plants |