Sturgeon making a comeback on Rainy Lake

They predate the age of dinosaurs by millions of years. They are one of the most ancient living vertebrates on the planet, and they are living right here among us.
The lake sturgeon (Acipenser fulvescens), the second-largest member of the sturgeon family found in North America, can be traced back 300 million years to the palaeonisciforms of the Devonian period.
They also are one of the longest-lived fish in North America, with a lifespan that may exceed 100 years. They are slow-growing and late-maturing, with females typically not spawning until they reach the age of 20—and then only doing so every four-six years.
The frequency of spawning also seems to decrease as the fish age.
With a surface area of 92,000 hectares, a mean depth of 9.9 metres, and a maximum depth of 49.1 metres, Rainy Lake and its watershed are, in many ways, an ideal environment for these great fish.
Each year, 8.3 billion cubic metres flows through the watershed, providing plenty of space and nutrition.
But the sturgeons’ future is by no means as secure as their past.
Wells Eugene (Gino) Adams recently completed his Master’s degree in wildlife and fisheries science at South Dakota State University. As part of his thesis, he conducted an exhaustive and comprehensive study of the lake sturgeon population in Rainy Lake in 2003-04.
His findings, while encouraging, make it clear the sturgeon population has been significantly affected by human activity in the area over the past century.
Decades of commercial harvesting have taken their toll, as have a number of dams built in the late 19th and early 20th centuries.
These man-made impediments permanently cut the fish off from some of their traditional territory and effectively isolated whole populations from each other.
Today, the lake sturgeon is listed as a species of concern by the Minnesota Department of Natural Resources.
Still, there are some encouraging signs.
“I think it’s [the sturgeon population] on its way back,” Adams said last week from his office in Columbia, Mo., where he is conducting further studies on the sturgeon population there on behalf of the U.S. Geological Survey.
“It’s a relatively healthy population compared to sturgeon populations across the country right now,” he added.
Over the two years of his research, Adams, working in conjunction with South Dakota State University, the U.S.G.S., the Minnesota DNR, and the Ontario Ministry of Natural Resources, caught and tagged a total of 272 fish in Rainy Lake.
Of these, 217 (67.4 percent) were caught below the Squirrel Falls Dam in the south arm. Fifty of those fish subsequently were recaptured throughout the duration of the study.
One of the most significant findings was the absence of older fish. In fact, the oldest specimen captured was a 60-pounder determined to be 59 years old.
Very few juvenile fish were caught, as well, but Adams concluded this was due to the size of nets being used to capture the fish and a general lack of information regarding the location and habits of juvenile fish.
“We’re kind of thinking we didn’t catch the small ones and might not have caught the big ones, either,” he surmised.
The lack of older fish was attributed to the massive toll taken by commercial fishing over the last 100 years, which was suspended in Minnesota in 1940 but remained in effect in Ontario until 1990.
Adams discovered the commercial harvest peaked in 1960 at around 2,500 kg and remained at that rate for the next 10 years. He also estimated an annual mortality rate during the years between 1965 and 1984 at 4.7 percent.
Combined with the slow maturation and spawning rates of sturgeon, Adams determined the population is only now beginning to return to the levels that existed a century ago.
As Adams stated in his thesis, “Older year classes in my analysis may have been substantially affected by commercial fishing while younger cohorts may have been too small to be commercially harvested in the 1980s and thus appear more abundant in the population age structure than would be predicted based solely on recruitment patterns.”
In other words, the maximum age of fish captured corresponds closely with the end of the commercial harvest and the population seems to be on the rebound.
Furthermore, close analysis of the body condition and growth rates of the fish indicates they are relatively plump and fast-growing compared to 32 other populations studied throughout North America.
However, Adams noted the apparent absence of very large and small fish may not necessarily be a true indication of the population structure.
He found sturgeon are great travellers with spawning migrations often exceeding 129 km, beginning with “ice-out” or sometimes before. At least one survey showed a migration of 402 km, so it can be difficult to predict where they will be at a given time.
By using radio transmitters with long-life batteries, it is hoped more will be learned about these migrations down the road.
Of course, Adams was not alone on this project. In fact, he had a great deal of help from a number of people and agencies.
One of those people was Larry Kellemeyn, an aquatic biologist with the U.S.G.S. currently stationed in Voyageurs National Park in northern Minnesota.
Like Adams, he was not particularly concerned by the apparent absence of juvenile fish. For him, the most encouraging finding in the survey was the number of sexually-mature fish netted.
“The fact that we’re seeing reproduction indicates there are certainly smaller fish there,” Kellemeyn said in a telephone conversation last Friday. “We just didn’t catch them.
“Just the fact we’re getting reproduction is a positive.”
Evidence of reproduction was particularly apparent in the area below Squirrel Falls, where a sizable percentage of the fish were found. Kellemeyn noted that particular area is an ideal spawning ground because of the abundance of broken rock and rubble—some of which was a by-product of the dam itself.
“It’s undoubtedly the best spawning habitat,” he noted. “It’s a large area with a combination of good [water] flow and structure.”
Kellemeyn also said the survey might never have happened at all were it not for the tremendous degree of co-operation among the four principal agencies involved.
“The most positive aspect of the whole thing is the fact that everyone was involved,” he enthused. “U.S.G.S. funded Gino [Adams] while the Ontario ministry and the Minnesota DNR provided terrific logistical support.”
Overall, Kellemeyn is optimistic about the future if current trends continue, although he warned it will be some time before the lake sturgeon population can be considered safe.
“My gut feeling is things are moving in the right direction,” he concluded.
Another key player in the survey was MNR area biologist Darryl McLeod, who is based in Fort Frances. McLeod played an active part in the tracking of fish that had been tagged with radio transmitters.
He concurred with many of Adams’ findings, and based on those, he believes there are, in fact, more fish of all ages in the lake than previously had been suspected.
“Based on that survey, we discovered the population is probably higher than we expected to see in the south arm, at least,” McLeod remarked, noting no surveys were taken in either the north arm or Redgut Bay.
“So we can confirm from that there has been consistent year-class production since 1960,” he added. “His [Adams’] conclusions were correct—that the population is still recovering, but there’s a general absence of larger fish.”
It seems there are some big ones out there.
Earlier this year, the MNR conducted its own sampling, with larger nets than those used in Adams’ survey. McLeod and his crew caught and released some large fish—including one that weighed in at 106 pounds.
McLeod estimated that fish to be around 80 years old.
He also suspects there even may be some 150-pounders out there. There certainly were in the past.
“Rainy Lake used to be almost entirely a sturgeon fishery back at the turn of the [19th] century,” McLeod noted. “Almost certainly there were larger fish caught back then, but we have no idea how big they were.
“I expect there are bigger fish in there and maybe we’ll see them as this population continues to recover,” he remarked.
McLeod said Monday that there is a report from two different walleye anglers, who caught and released two large sturgeon near Bear’s Pass last weekend, which might support his contention.
“The other big finding was that sturgeon move extensively throughout the lake,” he added.
In fact, the study showed they actually move beyond the lake where possible. It is believed, for instance, that the lake population is now interbreeding with fish in the Seine River system.
The MNR has sent DNA samples from both populations to Trent University in Peterborough to determine if that is the case.
“We need to include that [Seine River] population when we’re talking management,” McLeod said.
But the important thing, he stressed, is whatever the true numbers are, they are moving in the right direction.
Adams said there is still a great deal of work to be done in order to unravel the story about the mysterious lake sturgeon in Rainy Lake.
He noted there are no plans in the immediate future to do a follow-up study, although if the funds become available, a similar study may be done in Namakan Lake over the next few years.
In the meantime, Adams hopes others will learn from his research and appreciate the special resource found in Rainy Lake.
“It’s a pretty neat resource up there on that lake,” he concluded. “There’s not a lot that’s known about those mysterious fish in Rainy Lake, but I think there’s quite a few of them in there.
“The population is on the right track and if everybody allows it to be managed the way it should be, it should be a resource there for quite some time to come.”