Cindy Hagley, Great Lakes Environmental Quality Educator, University of Minnesota Sea Grant

Some of us prefer country living, with its lack of crowding, clean air and water, and wide-open spaces. Because in the country people are sparsely distributed, we tend to have to drive much farther to obtain the services we need. Others of us prefer the city, where high rise buildings make it possible for large numbers of people to congregate in relatively small spaces. In the “more productive” environment of the city, services are also concentrated in a small area and can be more easily obtained nearer to our homes. These services include shelter, food, water, medical care, security, and other basic human needs.

Fish are not so very different from us in terms of their basic needs, and, just like us, the number and variety of fish that occur in a particular lake are determined by the availability of essential “services.” In the case of fish, these include places to spawn and rear young fish, places for adults to feed, fish migration habitat, and vegetative cover for protection from predators.

The types of lakes we may enjoy most for swimming in are the least “productive.” In other words, they are less nutrient-rich and support less algae and fewer aquatic plants, fish, and the small aquatic animals (zooplankton) that many fish feed on.

Though not as much fun for swimming, a healthy, productive lake like this one is somewhat like our “city” environment. It can support high and diverse populations of fish.

What can you do to encourage good habitat conditions for fish in your lake? One of the most important habitat requirements for fish is aquatic vegetation. The following excerpt from Through the Looking Glass says it well:

“Any angler knows how important plants are to fish. Habitat created by aquatic plants provides food and shelter for both young and adult fish. Invertebrates living on or beneath plants are a primary food source. Some fish, particularly bluegills, also graze directly on leaves and stems.”

“Predatory fish cruise the shadowy plant beds in search of prey. The structure and density of the plant beds can determine whether predators will be well-fed or go hungry. Too few plants can limit the number of prey fish; plant growth that’s too dense can fence predators out.”

Through the Looking Glass… A Field Guide to Aquatic Plants Susan Borman, Robert Korth and Jo Temte 1997, 248 pp. http://www.wisc.edu/wisconsinpress/books/0519.htm

Just as in a city, where poor management can result in pollution, overloaded services, and a reduced quality of life, lakes receiving high concentrations of nutrients (phosphorus and nitrogen) from their watersheds can shift from being able to support high and diverse fish populations to a less stable, less diverse system. Excess nutrients can lead to the elimination of sensitive species, which are less able to cope with the adverse conditions that result from a lake becoming overly productive, or “eutrophic.” Long-lived species that reproduce slowly and require extended periods of stable conditions are most negatively affected in unstable, eutrophic lakes. Often, as lakes become more eutrophic, populations of the top predator species that we enjoy catching, such as walleyes, are reduced, and smaller less desirable species of fish increase.

Just as we work hard in our cities to develop effective comprehensive plans that will ensure a high quality of life in the future, we should work together to plan a healthy future for our lakes. Two of the most important steps we can take to ensure healthy fish populations are to maintain a healthy aquatic plant population and control nutrient inputs from the watershed.

Posted in Fish and Wildlife |