Posted September 24, 2021.
by Jennifer Johnson and Darren Kramer, Michigan Department of Natural Resources
Lake sturgeon are long-lived fish species that were once common in the Great Lakes.
However, over the past two centuries, lake sturgeon populations have declined dramatically due to several factors, including habitat loss due to the construction of dams. Once numbered in the Great Lakes region in the millions, the lake sturgeon population is now reduced to a few thousand fish. Lake sturgeon is currently listed as a threatened species in Michigan.
The Menominee River, part of the Wisconsin-Michigan border in the Upper Peninsula, is a large tributary of Green Bay on Lake Michigan and is home to one of the largest remaining populations of lake sturgeon in the Great Lakes . The sturgeon here have about 1,200 adult fish, compared to about 20,000 to 25,000 in the past.
Prior to the construction of several hydroelectric dams on the Menominee River in the 19th century, the lake sturgeon migrated upstream from Green Bay for about 70 miles to spawn, before encountering a natural barrier at Sturgeon Falls in Dickinson County.
Currently, their access to the river is interrupted by the Menominee Dam, located about 2.5 miles upstream from Green Bay. A second dam, Park Mill, is located approximately 1 mile upstream from Menominee Dam.
Mature adult lake sturgeon require specific spawning habitat typically found in rivers and are prepared to make long migrations to reach these optimal spawning sites.
“Dams are considered to be one of the main obstacles to the success of sturgeon recovery efforts in the Great Lakes, as adult fish cannot access river spawning habitat and necessary critical habitat.” to support juvenile fish, âsaid John Bauman, fisheries biologist for the Michigan Department of Natural. Resources.
Lack of suitable lake sturgeon spawning and nursery habitat downstream of Menominee Dam are likely key factors limiting lake sturgeon population recovery.
Luckily for the lake sturgeon, there is extensive habitat for adults and juveniles above Park Mill Dam to the Grand Rapids Dam, located about 19 miles upstream.
Given these facts, the question for fisheries managers was how to reconnect the adult lake sturgeon of the lower Menominee River to the abundant spawning and nursery habitats upstream of the two dams?
In some situations, removal of the dam may be an option to restore access to the river if the dam is no longer useful. However, the Menominee and Park Mill hydroelectric dams are viable producers of renewable energy and are not candidates for removal.
So, if the dams cannot be removed, how do you restore lake sturgeon access to habitats upstream of the Menominee River?
It took a creative and talented team to come up with a new and unique idea.
In the early 2000s, a collaborative partnership between Eagle Creek Renewable Energy (owner of the Menominee and Park Mill Dams), the US Fish and Wildlife Service, the Wisconsin and Michigan Departments of Natural Resources, and the River Alliance of Wisconsin formed Michigan Hydro Relicensing. Coalition to determine how best to reestablish the link between adult lake sturgeon in the lower Menominee River and upstream habitats.
The overarching goal of the effort was to increase lake sturgeon recruitment – the process by which small, young fish outlive larger, older fish. It was assumed that these recruits would survive and contribute as adults to the overall sturgeon population in Green Bay and more widely in Lake Michigan.
The team’s work resulted in the construction, in 2015, of a âfish elevatorâ located at the Menominee dam. The elevator was designed to capture adult lake sturgeon for transfer upstream of Menominee and Park Mill dams.
The fish elevator was built in an empty bay at the Menominee Dam power station. In the bay is a rectangular metal hopper, measuring 10 feet by 15 feet. The hopper can be lowered to the bottom of the river.
Water from above the dam flows through the hopper area by opening an upstream valve, creating an “artificial river” to bring the lake sturgeon into the hopper. A fixed door at the head of the hopper prevents fish from entering further into the dam.
The downstream end of the hopper is open for fish to enter and exit until a door is lowered, trapping the fish inside. The hopper is lifted approximately 30 feet to the upper level of the plant using an electric winch. A door on the side of the hopper opens, emptying the water and fish into a sorting bin.
From there, unintentionally caught fish species are sorted and returned downstream via a water pipeline. Lake sturgeon are visually inspected for any previous injury or disease, measured and tagged, if no previous tag is observed.
Sex and spawning conditions are determined using an ultrasound machine like those found in veterinary clinics. Most male lake sturgeons spawn every one to two years, and females spawn every three to five years. Fish that are not ready to spawn during the next spawning period (late April to mid-May) are returned downstream.
Fish ready to spawn are moved to an adjacent retention pond in the plant pending transfer upstream. The minimum lengths of fish required for transfer are 45 and 50 inches for males and females, respectively.
When transferring lake sturgeon upstream, the fish are loaded into a custom trailer and transported approximately 2 miles to a boat launch above Park Mill Dam, located on the Michigan side of the Menominee river. There, the trailer is pulled back into the river and the adult sturgeons are released to continue their upstream migration.
Since 2015, silo and transfer operations at the Menominee dam have taken place every year in spring (mid-April to mid-May) and in autumn (end of August to end of September).
âLake sturgeon catches vary considerably from year to year and between spring and fall,â said Elle Gulotty, MNR’s fisheries biologist. âOver time, we have learned more and more about the efficient operation of the fish elevator.â
Over the past six years, the number of fish transferred upstream has increased from a low of 25 in 2015 to a high of 147 in 2019.
Lake sturgeon transferred in the spring spawn during this period, while fish transferred in the fall spend the winter in the river before spawning the following spring. About 90% of sturgeon transferred upstream remain there for at least one spawning period before migrating downstream to Green Bay.
During this migration, lake sturgeon cross the Menominee and Park Mill dams through gates open to the dams or through fish diversion structures specially constructed at each lake sturgeon dam.
Watch a video showing the time-lapse construction of the sturgeon structure downstream from Park Mill Dam at https://www.youtube.com/watch?v=A1J4iDc55to.