Gone for decades, lake sturgeon are once again spawning in the St. Louis River, not far from downtown Duluth.
They are the largest fish in Lake Superior, reaching seven feet in length and exceeding 100 lbs - Native Americans called them the Buffalo of the Water. But despite their great size and longevity (lake sturgeon can live for more than 100 years), they couldn’t withstand commercial fishing or polluted water. By the mid 20th-century, sturgeon were gone from western Lake Superior and they are threatened or endangered throughout most of their original U.S. range.
They’ve returned to the St. Louis River thanks to the determined efforts of conservationists that began more than a quarter century ago. It was a joint effort that included The Nature Conservancy, the Minnesota and Wisconsin departments of natural resources, the U.S. Fish and Wildlife Service, the Fond du Lac Band of Lake Superior Chippewa and many others.
“It’s a huge success story,” says John Lindgren, a fisheries biologist with the Minnesota Department of Natural Resources (DNR). Lindgren has been carefully monitoring the sturgeon’s return to the St. Louis River.
The St. Louis River forms the largest estuary on Lake Superior, and historically was prime sturgeon habitat. Lake sturgeon from western Lake Superior ascended the river to spawn in its shallows and newly hatched fry grew along its shorelines. The young fish swam downstream to Lake Superior where they slowly matured into adults: 20 or more years later they’d return to the river to spawn.
But pollution from industries associated with the twin ports of Duluth, Minnesota and Superior, Wisconsin degraded the waterway and wiped out all lake sturgeon in the St. Louis River and western Lake Superior. The Clean Water Act in 1977 resulted in a clean-up and soon the river and western Lake Superior were ready for sturgeon again. Lake sturgeon were restocked in the river starting in 1983.
Year after year, Lindgren helped with the restocking effort that continued for 18 years. A total of more than 142,000 fingerling and 728,000 fry were released through 2001. Then it was time to “watch and wait,” Lindgren said.
Would the introduced sturgeon eventually return to the St. Louis River to spawn?
In 2007, adult sturgeon were seen 26 miles upstream from the river’s mouth below the Fond du Lac Dam. They were back, but would they spawn? The habitat needed to be just right and that required restoration of their spawning grounds below the dam.
Sturgeon like to spawn behind large river rocks as turbulent, well-oxygenated water is ideal for their eggs to adhere to the streambed. In August 2009, rocks were strategically placed below the dam to create riffles in the river that were needed for optimum spawning habitat.
It was a big job – 1,500 tons of rocks were required. The Nature Conservancy coordinated the $150,000 restoration project that was funded by the Environmental Protection Agency and the U.S. Fish and Wildlife Service through a $75,000 grant from the National Fish and Wildlife Foundation, matched by in-kind contributions from the Minnesota DNR.
The Conservancy also protected Clough Island, a 358-acre island in the very heart of the St. Louis River estuary, downstream from the spawning grounds. The island’s shoreline habitat is an important nursery area for young lake sturgeon. Popular game fish such as walleye and smallmouth bass also use the waters surrounding Clough Island and will spawn in the rocky areas created for the sturgeon below the dam.
In June 2011, biologists placed nets below the restored spawning grounds and caught tiny fry sturgeon – proof that the big fish seen in the river were successfully spawning. How many sturgeon have hatched is unknown. “If you find ten fry, some say there are really ten thousand” notes Lindgren.
If all goes well, those fry will mature in Lake Superior and return to the St. Louis River to spawn to create a new generation of lake sturgeon.
What isn't clear, however, is how many lake sturgeon are now utlizing the river and western Lake Superior. To find out, Minnesota and Wisconsin fisheries staff inserted passive integrated transponder or PIT tags, similar to the ones placed under the skin of pets, into approximately 200 adult lake sturgeon in 2016.
The tags were purchased by The Nature Conservancy, thanks to a grant from the Biodiversity Fund of the Duluth Superior Area Community Foundation.
In coming years, the tags will allow researchers to estimate the population of the area's lake sturgeon for the first time since they started their recovery. The information will be used to guide management and restoration efforts.
The comeback of lake sturgeon in the St. Louis River shows that through science and collaboration that even our most impaired waters can be restored for the benefit of both people and nature.