Sturgeon solutions: Biologists seek reasons for lack of fish’s reproduction on St. Louis River
FRENCH RIVER, Minn. - The St. Louis River has a healthy population of adult lake sturgeon, but those fish are not producing the numbers of young fish that biologists had hoped to see. Few adult females are returning to spawn, and biologists have ...
FRENCH RIVER, Minn. - The St. Louis River has a healthy population of adult lake sturgeon, but those fish are not producing the numbers of young fish that biologists had hoped to see. Few adult females are returning to spawn, and biologists have found little evidence of young sturgeon being produced, said Dan Wilfond, fisheries specialist with the Minnesota Department of Natural Resources at French River.
"Our stocked fish are doing well, but it's our recruitment (of young sturgeon) we're concerned about," he said. "We have this apparent lack of females, and we're seeing very few juveniles ... That's disconcerting."
Fisheries biologists have noted these trends after the first 18 months of a 10-year hydro-acoustic study in which 105 adult sturgeon have had transmitters - called tags - surgically implanted in them so their movements can be monitored.
Another 45 sturgeon will be fitted with transmitters this spring. The movements of lake sturgeon in the river and in Lake Superior are detected when the tagged sturgeon pass by any of 40 acoustic receivers in the river and nearby waters of the lake, or when they pass by receivers placed by other agencies lakewide.
Lake sturgeon, long ago extirpated in the St. Louis River by overfishing and habitat degradation, have been stocked in the river by the Minnesota and Wisconsin DNRs from 1983 to 1994 and from 1998 to 2000.
Stocking to resume
After seeing evidence of low reproductive success among sturgeon in the river, fisheries officials with the Minnesota and Wisconsin DNRs plan to resume stocking them in the river in 2019.
"The big thing is to try to rehabilitate a population we started rehabbing 30 years ago," said Paul Piszczek, Wisconsin DNR fisheries biologist in Superior. "The most recent documents show we need several more year classes to hit our target. And our stocking efforts should do better because of the cleanups we've had (in the river) over the years."
The fish will come from the Sturgeon River in Michigan's Upper Peninsula, a tributary of Lake Superior, in cooperation with the state of Michigan and the U.S. Fish and Wildlife Service, Wilfond said. They will be stocked in the fall each year as fingerlings.
Stocking had been ended after 2000 so that biologists could eventually see whether natural reproduction was occurring among the river's sturgeon.
Some studies on sturgeon reintroduction suggest that Minnesota and Wisconsin may not have stocked sturgeon for enough years, Wilfond said.
"We stocked 13 year classes," he said. "(Research indicates) we may need 25-year classes. Our population size is likely too small to sustain the population."
Sturgeon are extremely slow to reach sexual maturity - males at 15 to 25 years and females at 20 to 30 years.
Of 138 sturgeon captured near the Fond du Lac Dam by DNR officials last year, just three were females. Some research has shown that female sturgeon spawn every three to five years once they mature, Wilfond said.
"But Lake Superior is cold and unproductive," he said. "It could be six or eight or 10 years before they come back to spawn. That certainly makes it challenging to manage these fish if only a small percentage are coming back to spawn in any given year."
Biologists also suspect that perhaps legacy contaminants from decades ago in the St. Louis River may be compromising eggs and larval sturgeon in the river.
"There maybe an awful lot of legacy contaminants in that river, and that can enter the food chain," said Brian Borkholder, fisheries biologist at the Fond du Lac Band of Lake Superior Chippewa.
Research on possible contaminants in sturgeon will begin within weeks. It will be done by Jon Doering, an aquatic toxicologist at the Environmental Protection Agency's Midcontinent Ecology Laboratory in Duluth.
Doering will analyze blood and mucous samples of adult sturgeon in the river, he said. By analyzing those samples, he can determine whether the adults are likely able to reproduce successfully. He'll also be able to determine the extent to which chemicals in an adult female sturgeon might be passed on to her eggs.
"We can determine, for instance, if the chemicals are causing 20 percent of the eggs to die, or 80 percent to die," Doering said. "We can predict the magnitude of the effect, and whether legacy contaminants are a major factor, a minor factor or no factor at all."
Migrating to the lake
The acoustics research showed that of the 105 sturgeon tagged in 2016 and 2017, 50 of them migrated out to Lake Superior and remain there, while 55 are still in the river. More than 60 percent of the sturgeon that migrated to Lake Superior made significant movements along South Shore, some as far as the Keweenaw Peninsula. Some tagged sturgeon that left the river have not been detected at any other receivers in Lake Superior.
"There are vast amounts of Lake Superior that have no receivers," Wilfond said.
Most of the fish that moved into Lake Superior left the St. Louis River in June 2016 or 2017. All 105 sturgeon that had acoustic tags surgically implanted have been detected by receivers, Wilfond said, indicating excellent survival after their surgeries.
Through sampling associated with the acoustic project, researchers also learned some things about the genetics of the St. Louis River's sturgeon. In past stocking efforts, most of the sturgeon originated from Wisconsin's Wolf River, a tributary of Lake Michigan. More recent stockings were from the Sturgeon River in Michigan's Upper Peninsula.
Of 361 sturgeon sampled during the past two years, 85 percent were of Wolf River ancestry, Wilfond said.
"That's no surprise, because that's the predominate strain we stocked, and we stocked a lot more of them than the Sturgeon River fish," he said.