Fish structures in Michigan's Inland Lakes or Rivers; "If you build them, will they come?" The simple answer is yes, but is it always appropriate?
Fishermen, lake associations and lakefront residents frequently approach fisheries biologists asking to add a variety of "things" to their lake to make fishing better. However, "things" proposed were old boats, refrigerators, Christmas trees, pallets, human-made plastic structures, even junk cars. Prior to adding any structure, a preliminary analysis should be conducted to determine if woody structure abundance is limiting production, recruitment and/or growth of various fish species. Another important piece of information would be the fish population structure and amount of fishing pressure. Finally, if the lake does have a lack of woody structure, why?
Generally, woody structure is lacking in developed lakes. Where the shoreline was formerly wetlands, native grasses, shrubs and trees, we now have sea-walls, rip-rap, and manicured lawns. Also, when shorelines are converted to residential uses, the woody structure and/or vegetation that were in the near-shore zones are summarily removed. To confirm this fact, one only needs to look at our remote Upper Peninsula lakes. These lakes have abundant submerged trees and/or treetops that have fallen into the lake naturally, from undeveloped shorelines.
Say we have determined there is a scarcity of woody structure in "Clearcut Lake." So, what type of woody structure should we add, and where should we place it?
A warning: Any and all structures placed in lakes require a permit from the Michigan Department of Environmental Quality. The placement is regulated by MDEQ under the Natural Resources and Environmental Protection Act, 1994 PA 451, as amended; Part 301, Inland Lakes and Streams. This Part is administered by the Land and Water Management Division-MDEQ.
What should be placed? Placing whole trees or major portions thereof is recommended. No broken concrete, treated lumber, plastics, pallets or Christmas trees. Natural is best! There are two sources of whole trees or portions. First would be to cut them along the adjacent shoreline, but for every one cut, please plant two as replacement. The other source would be to import whole trees or portions, if not available on the adjacent shoreline. We recommend that any woody structure placed in the near-shore zone be anchored. Approved anchor types would of biodegradable material, such as rope, burlap bags or duck bill anchors. Rock would also be acceptable, as it adds structure for certain fish species.
Where should they be placed? Any woody structure restoration or enhancement should be concentrated in the near-shore area or on drop-offs. The near-shore zone of all lakes is the most productive. Productivity is partially dictated by the condition of the shoreline area. The near-shore zone is where most spawning takes place, the nursery area for young fish, and feeding area for adult fish. Those are the reasons diverse habitats, including aquatic vegetation and woody structures are needed in near-shore zones. A healthy near-shore ecosystem should have about 50 percent of the area in cover, whether it is vegetation or woody material.
Placing woody structures in deep water only concentrates fish, making angling easier and increasing the potential for over harvest. It does not produce more fish. Therefore, placing wood structures in deep water would be a very distant second priority and in most cases is strongly discouraged.
The potential benefits of woody structures are increased angling success, enhanced spawning success, and increased habitat diversity. Again, in almost all cases, addition of structures will not automatically enhance production, recruitment or growth of fish significantly and may not be worth the effort or dollars expended.
Streams are another story, but woody material is likewise important. It is cover for fish to avoid such predators as Great blue herons, belted kingfishers, mergansers and river otters. It is also a source of carbon, which is the basic building block of all life. The woody material is also home to many aquatic insects, which is fish food. In my former position, we added woody material where appropriate. We used both natural tree material and constructed wood structures. The latter were especially popular with brown trout, which we nicknamed brown trout condos.
So, the answer is yes to "If you build them will they come?" All that said, proper placement is very important and can lead to enhanced stream trout populations.
There are alternatives to installation of woody structures, many of which were outlined in Waterfront Management 101-Part I. Lake associations can hold educational events that promote proper shoreline management techniques. A lake association may hold riparian buffer contests to restore appropriate habitat. Use proper riparian management techniques when developing lake front lots. Every little bit counts!