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Connections matter: The importance and status of aquatic connectivity for fish in Michigan
August 16, 2022
MI Environment is featuring this story by Gary Whelan, of the Michigan Department of Natural Resources, from the State of the Great Lakes report.
The Great Lakes are an amazing system that, like any other system, require connected component parts to function. In the Great Lakes case, its component parts are its many tributary watersheds. These watersheds are conduits for a range of materials from the landscape that feed the Great Lakes, including water, organic material, food for energy, sediment, nutrients, and woody debris.
To complete this critical function, a watershed’s rivers and streams must be connected to each other and the Great Lakes. Each river and stream segment needs to be connected to its adjacent riparian area to efficiently feed materials to the Great Lakes.
Sixth Street Dam, Grand Rapids, Mich., 2013. (Photo courtesy of Michigan Department of Natural Resources)
The Great Lakes historically provided energy and nutrients back to the watersheds using fish as the primary mechanism but now accomplish this in a more limited way due to hydrologic systems being fragmented. Great Lakes watersheds depend on fish returning nutrients and energy back into tributary streams through adfluvial fish that live in lakes to maximize growth and spawn in rivers. (Adfluvial fish spawn in tributary streams where the young rear from 1 to 4 years before migrating to a lake system where they grow to maturity.)
Regardless of where fish live most of their lives – the Great Lakes or tributary streams – all fish need to move to complete their life history.
Stream fish move to find:
• the best feeding locations to maximize growth.
• cover to avoid predators.
• refuges to avoid harsh winter, drought and flooding conditions.
• the best spawning conditions
These movements also ensure that fish can fully function throughout their life spans. This includes species that are:
• opportunistic and quickly colonize habitats and often have short life spans.
• nesting species with medium life spans and require the ability to move to spawning areas.
• adfluvial or potamodromous (use bigger streams and rivers to grow and spawn in smaller stream) species that can have life spans that range all lengths.
• late maturing, with periodic spawning that have very long lives.
Historically, Michigan’s Great Lakes tributaries were full of fish from the Great Lakes, particularly in the spring, and in some cases today, they still are. Nearly every Great Lakes fish species had an adfluvial population. When reproduction occurs in different areas, risk of reproductive failure is minimized and catastrophes avoided.
Native Americans took prime advantage of this readily available, early spring protein source. A study of the distribution of their villages clearly shows that they were often located on key spawning areas for adfluvial fish. There are many accounts from early European settlers of wagon full loads of suckers being taken from the Saginaw River and Grand River by early settlers.
Lake sturgeon were documented from many tributary streams with records indicating fish ran the Grand River to Eaton Rapids, the Menominee River to Sturgeon Falls, the Kalamazoo River to Albion, and the Tittabawassee River to Sanford. Even lake trout were documented in the St. Joseph River at Niles. Masses of fish moving upstream from the Great Lakes was likely staggering to see prior to dams, landscape scale logging, overharvest and water pollution.
Today, fragments of Great Lakes tributaries remain and only a few rivers and streams are fully connected, including the Ford, Two Hearted, Pere Marquette and Carp Rivers. Even with these fragments, the numbers of fish moving in the spring is large.
Michigan has approximately 72,000 miles of flowing water that is now highly fragmented. These waters have 2,400 dams listed in the Michigan Dam Database, and this list does not include all of the dams on our streams. Only a very small number (about 25) have any type of fish passage, and while fish passages at dams certainly helped move some fish past these barriers, they are a poor second choice. Dams disrupt the movement of sediment, woody debris, and organic matter from the landscape to the Great Lakes, storing these landscape outputs in their respective impoundments.