A Study of Lake Sturgeon

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By Nancy A. Auer

Michigan Natural Resources: March/April 1993
A. fulvescens

For the past six years, a biologist from Michigan Tech has researched the spawning habitats of this threatened species.

In the early morning hours of April 21, 1987 we waited patiently by the powerhouse retaining walls at the Prickett Dam on the Sturgeon River about 10 miles southwest of L'Anse in Michigan's Upper Peninsula. It was just 11 days after ice-out on nearby Portage Lake and as they had done for centuries, the lake sturgeon had begun to make their way up the river to spawn. The powerhouse wouldn't start up again until 8:00, so we stood with our dip nets, ready to scoop up any sturgeon that came within reach during the next couple of hours. Only a single adult male sturgeon was captured and tagged that day. It was 49.5 inches long and weighed 27 pounds. The following day we caught another male, 55 inches long and 36 pounds. In addition to the identification tag, we fitted this fish with a radio transmitter that would allow us to track its movements in the river system. These fish were the beginning of my research project that was only the third studied population of this threatened species in Michigan and the only group which was not landlocked.

The lake sturgeon is the largest and oldest fish to live in the Great Lakes. A truly primitive fish, the fossil record of this species shows that it has remained unchanged since it first evolved some 100 million years ago. The sturgeon has a cartilaginous skeleton covered by large, bony plates. A strong shark-like tail propels the fish along the bottom of large sandy lakes and rivers where it searches for food.

Lake sturgeon were once abundant throughout the Great Lakes region. Unfortunately, during the early years of commercial fishing that began in the 1830s, the sturgeon was considered a trash fish by fishermen because of the damage it did to their nets. Consequently, thousands of sturgeon were stacked on beaches and left to rot in the sun or burned in great pyres.

By the 1860s, the value of sturgeon flesh, eggs and by-products such as oil which could be used to manufacture paint led to an increased market demand and subsequent heavy exploitation. The population declined rapidly. Eventually, the commercial and sport fishery for lake sturgeon was closed in 1929, but unlike other fish species that often recover once fisheries are closed, there has not been any significant improvement in lake sturgeon populations. Ironically, those characteristics that have allowed the lake sturgeon to persist since the time of the dinosaurs-long life, large size and remaining a juvenile for an extended period-are characteristics that also prohibit the species from making a rapid recovery. The lake sturgeon is a unique species of fish in that it is a late-maturing, slow-growing species. Male lake sturgeon reach sexual readiness at about 45 inches or 15 to 20 years of age. They then spawn only every three to five years. Females must reach a length of about 55 inches before they first spawn, usually occurring at about 25 years of age. Once mature they spawn only every five to nine years.

Destruction of habitat necessary for juvenile growth and damming of rivers used for spawning were also major factors in limiting the recovery of lake sturgeon. Sturgeons spawn in upstream rapids of large rivers and their migration routes to many historic spawning sites were blocked when hydropower and industrial development blossomed in the early 1900s.

Today, while most remaining stocks of lake sturgeon in the United States are restricted in movement by dams, we are fortunate that the sturgeon which utilize the Sturgeon River for spawning may be the widest flee-ranging population known to exist in all of North America. Each spring these fish come to spawn over a period of two to three weeks in a small set of rapids located some 43 miles above the river's mouth. During the first two years of my study which began in 1987, we surveyed only the upper rapids area of the river. Then in 1989, we began to survey both the upper and lower rapids which enabled us to handle a much greater number of adult sturgeon while the fish were at the spawning site. Over the entire six-year study period, 567 adult lake sturgeon have been fitted with an identification tag. In addition, in 1987 and again in 1990 we fitted a total of thirty fish with a small, cigar-shaped radio transmitter which allowed us to document the duration of the lake sturgeon's stay in the study area as well as their movements outside the spawning ground.

Each fish's transmitter emitted a unique signal which could be detected with the use of a hand-held antenna and receiver. An automatic data logger located near the mouth of the Sturgeon River, recorded the time and transmitter frequency as each fish passed downstream. Once the lake sturgeon passed the recording station, my assistant Ellen Lutz and I began tracking the fish by boat in the connecting Portage Lake, Torch Lake and out into Keweenaw Bay.

The telemetry study, supplemented with information obtained by tag returns, has shown that lake sturgeon travel great distances. Some adult fish spawned and moved back down the 43-mile river system in as little as four days. Upon reaching the lake environments previously mentioned, several sturgeon appeared to spend the summer "resting" in those nutrient rich environments before moving out into Lake Superior in the fall.

In 1989, an identification tag was found attached to a trap-net line by a commercial fisherman in Munising Bay 43 days after it had been attached to a female lake sturgeon at the spawning site. That fish had traveled more than 150 miles before her tag had become entangled in the trap net. Two years later, another lake sturgeon that we tagged was captured and released by the same fisherman, once again in Munising Bay.

Our tagging and tracking of lake sturgeon over the past six years has shown that many adults which spawn in the Sturgeon River return to Keweenaw Bay. One male sturgeon that we tagged in April, 1987 was captured and released by fishermen in the bay later that year. This same fish was seen again in 1990 and 1992 when it returned to spawn at the Sturgeon River site. Altogether 14 identification tags have been returned from lake sturgeon captured in Keweenaw Bay, which some 100 miles from the spawning site.

Even supposedly landlocked sturgeon have appeared in some rather unexpected places. For more than 50 years, lake sturgeon have been landlocked in the Lake Winnebago area of central Wisconsin. Their movement into Green Bay has been blocked by numerous dams and locks on the Fox River. However, one fish was captured in Lake Huron eight years after being tagged by the Wisconsin DNR and another sturgeon was taken in Lake Erie five years after it was tagged. Incredibly, both fish passed through all 17 locks and 14 dams on the Fox River and traveled distances of 500 and 850 miles before their capture.

My research of the Sturgeon River lake sturgeon has been partially funded by grants from the Michigan Nongame Wildlife Fund and Living Resources Small Grants Program. Because few long-term studies on lake sturgeon have ever been done, and none have ever been done on free-ranging populations, I plan to be back at the dam site with my research assistants this spring to continue my study of these fish in hopes that the information learned will be beneficial to the long-range survival of this ancient species.