Department of Natural Resources
Creeks, streams and rivers flow throughout Michigan's many landscapes. On their path from upland areas to the Great Lakes, these waters encounter different types of structures that block or interrupt the movement of not only the water itself, but also the aquatic organisms that live in these waters rivers. These blockages can cause problems for the organisms that live in the streams and are often referred to as "connectivity issues".
How do connectivity issues affect things that live in Michigan's rivers and streams?
"Some creatures, such as fish, have the ability to easily move about in the aquatic environment," said Kyle Kruger, a fisheries biologist with the DNR, Fisheries Division's Habitat Management Unit. "Other creatures, such as clams or mussels, are not able to move as freely; yet, because of their dependence on fish for part of their life cycle, still need free-flowing rivers and streams. Other creatures need different parts of the river during different parts of their life, such as different nursery habitats and spawning habitats. Access to these various habitats is often critical for aquatic organism survival."
One of the more notable examples of this need to access specific habitat types is the migration of salmon or steelhead from the Great Lakes into Michigan's rivers and streams for spawning. These fish require coldwater streams for laying their eggs and then for young fish to live and grow until they move to the Great Lakes to continue their life cycle. Less obvious, but just as important, is the movement of fish from one part of a river to another for specific habitat types for spawning or rearing of young (nursery habitat).
However, many times there are obstacles in rivers and streams. Dams and culverts are very common in Michigan and can block movement of aquatic organisms. Dams that do not provide specifically for fish passage frequently block all upstream fish movement. Culverts that pass under roads may appear to allow fish to move through them; however, this is not always the case. If a culvert is improperly installed, conditions can be created that block some or all upstream aquatic organism movement. A culvert that is installed too steeply can have water moving through it so fast that fish cannot swim through it. Or, if the culvert is "perched" or raised high enough above the river to create a large drop, fish that cannot jump high enough are prevented from passing upstream.
"Another situation where connectivity affects fish is when they need to move to different habitat on a seasonal basis," Kruger explained. "Some fish may need to move to find different habitat during the winter versus the summer."
As an example, trout need cold water to survive. During the winter they may move to larger sections of the river to find proper winter cover, but during the summer, those stretches of river may become too warm, so the trout need to move up into smaller tributaries that may be colder. Barriers like dams and impassable culverts can become a problem for these fish. They may be able to move downstream over dams or through culverts to find good winter habitat, but when they cannot move back up to the colder water in the summer, conditions become limiting for the fish and they can perish.
During an aquatic organism's various life stages, if any part is interrupted by the inability to reach the proper habitat, they will not flourish. These failures can lead to the reduction in populations or even loss of some species completely from some rivers or streams or at least portions of rivers or streams.
By removing old dams that are no longer providing benefits or are unsafe - or by replacing culverts with bridges or properly sized and installed culverts - the problems associated with connectivity can be reduced or eliminated. This can lead to healthier populations that are naturally reproducing and sustainable.
Correcting connectivity issues will lead to healthier, more robust fish populations that do not require stocking and will be better able to support fishing opportunities, rather than populations that are negatively affected by the presence of unnecessary dams or culverts that are not properly installed. Correcting connectivity issues also reduces threats to freshwater mussels, one of the most endangered groups of animals in North America.
Fisheries Division's Habitat Management Unit has been working on correcting connectivity problems where practical in Michigan's rivers and streams.
"We've worked with other agencies and non-governmental organizations to evaluate the status of many of the culverts and dams in Michigan," said Kruger. "A number of databases have been developed to collect information on these structures that may be blocking fish movement."
He goes on to explain that fieldwork is used to evaluate the most problematic structures and then a plan is developed to address connectivity blocks. Fisheries Division often works with partners to collaboratively make decisions on how to approach these problematic structures and also to seek funding and ultimately fix problems.
"In many cases, solutions were developed and poorly performing culverts and obsolete dams have been removed," he said. "This has opened up hundreds of miles of streams to the movement of fish."
Fisheries Division, and the DNR, believes by reconnecting Michigan's rivers and streams we are improving the aquatic environment and creating a better future for not only the creatures that live in our waters but also for the public that enjoys the recreational and environmental values of these waters.