The travels of lake sturgeon

The DNR has tagged hundreds of sturgeon in the St. Croix to track their age, movements, and more.

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Angler Doug Smith of May Township caught fish 888030 in October 2018. It was originally tagged on August 17, 2012 upstream of the Taylors Falls dam about 32 miles upstream from where it was recaptured in Bayport. That means it went over the dam! (Photo courtesy Ray Valley)

The Lake Sturgeon (Acipenser fulvescens) is an ancient fish that has roamed Minnesota’s large lakes and rivers for millions of years but almost went extinct in the early 1900s due to human exploitation. Populations in the St. Croix River have rebounded strongly after a century of conservation efforts and harvest restrictions.

Because of their immense size, strength, and ease to catch, the St. Croix supports a hugely popular sturgeon catch and release sport fishery, both in fall and winter.

The MN and WI DNR partner on sturgeon research and management programs including a long running tagging study that is designed to learn more about the sturgeon population size and movements. Tagged fish have been caught numerous times by anglers and each have an interesting story.

Metro River Specialist and DNR Fisheries Biologist Joel Stiras spends a good part of his days in fall and winter responding to anglers who report their tagged fish and are curious about the history of their fish. I caught up with my old colleague and asked him some questions about the sturgeon tagging program.

So many of us who fish sturgeon in the St. Croix have caught one to several tagged fish. How many tagged fish might be roaming around out there and how long has the tagging program been going?

From 2003-2017, 714 Lake Sturgeon were tagged in the St Croix River. I’m sure a few fish have died, and we know a few have lost their tags. There are a few fish out there with the wire still in the dorsal fin, but the plastic tag broke off. A few others where anglers removed the tags, or instances where tags got caught in landing nets. But the number of tags at large should be around 700 not counting fish tagged by the Lake City office or the WI DNR.

How many other fisheries area offices are involved and over what stretch have fish been tagged?

I’m not sure on specifics, but the Hinckley DNR office started tagging in the Kettle River, then moved into the St. Croix and Snake rivers, all upstream of the Taylors Falls Dam.

While that dam is an impassable barrier for fish traveling upstream, on rare occasions, fish tagged upstream of that dam are caught and reported by anglers providing some proof that Lake Sturgeon can survive the plunge over that dam.

The East Metro office has been tagging Lake Sturgeon in the lower St Croix River, from Taylors Falls to Prescott, WI. One other office, the Lake City office, has been tagging Lake Sturgeon in the Mississippi River, from Pool 3 down to Pool 8.

What are the goals of the tagging program?

Initially, the tagging goals were to tag as many fish as possible in an attempt to get a handle on how many Lake Sturgeon were actually out there. Traditional survey methods caught few, if any, Lake Sturgeon.

After the Hinckley office had such great success angling for Lake Sturgeon in the Kettle River, attempts were made to sample St. Croix Lake Sturgeon by targeted angling. The hope was to calculate a population estimate based on the number of individuals captured, the number marked with a tag, and the number of marked fish that were recaptured. However the number of individuals captured and recaptured in a given year were not sufficient to compute a reliable population estimate and too many assumptions were violated for a model to accurately estimate the size of the population.

Wire and tag still intact after 11 years, 42”-long fish 87154 was recaptured on 10/27/2018 for the second time on the author’s boat by May Township resident Doug Smith. The fish was 30.5” when it was tagged in 2007 and mark and recapture locations were only 3.5 miles apart in the Bayport area. (Photo courtesy Ray Valley)

Some of the other goals of the tagging program were to observe fish movement, where fish were recaptured after they were tagged. Another goal was to document growth rates between capture events. Some effort was made to collect Lake Sturgeon fin rays to estimate the age of the fish to develop a length-at-age database. However, poor agreement between biologists on the age of a given fish has proven to be a hurdle that makes it difficult to develop such a database.

Science aside, the Lake Sturgeon tagging program has been very popular with anglers, providing a history on where tagged fish came from, how many times it has been caught, and where it has been caught before.

How many fish have been recaptured by anglers? How many fish have been recaptured multiple times? Which fish holds the record for number of times caught?

So far there have been 556 reports of tagged Lake Sturgeon. Almost all of those reports are from the angling public. In a few instances, commercial fisherman will catch and release tagged fish, or the WI DNR will catch some. I count all reports of tagged fish as public reports unless we have a specific crew of people on sight to handle and process the fish exactly how we do when we catch the fish.

Of the 714 tagged Lake Sturgeon, 302 have been caught at least once. 154 have been reported more than once. That is just what has been reported. Tagged fish are caught and not reported.

The current record for number of times a Lake Sturgeon has been reported caught is seven times. Four fish currently hold that record.

I’ve seen population estimates of approximately 5,000 fish in the St. Croix. That seems low. How confident are you in this number? Do you have any idea how much the population in the river fluctuates?

The last population estimated I calculated was 5,967 Lake Sturgeon with a 95% confidence interval [a type of statistic] of 4,414 on the low end and 8,067 on the high end. That was for all sizes of sturgeon and I think it greatly under-estimates the true population size. In short, I’m not confident in that number.

That estimate is based on 15 years of data and violates about every assumption for any [population] model. That estimate doesn’t account for immigration, emigration, mortality, or reproduction. We are currently working with the WI DNR to see if we can come up with a one or two year tagging protocol to get a better estimate and I will be doing some exploratory field work in 2022.

Fish 888030 was originally tagged on August 17, 2012 upstream of the Taylors Falls dam about 32 miles upstream from where it was recaptured in Bayport.

It’s hard to know how much the population fluctuates for a fish that lives so long and can travel hundreds of miles. Because they can live so long and are such a hardy fish that can be caught multiple times, I don’t think the population level fluctuates much. Based on our tagging data, as well as our telemetry data, we know Lake Sturgeon will leave the St. Croix and others will travel to the St. Croix. Most Lake Sturgeon living in the St. Croix generally stay there. Some may leave for short periods, some may leave forever.

We’ve had tagged fish caught in the Blue Earth, Mississippi, and Chippewa rivers and have seen transmitter fish from Pool 4 of the Mississippi make brief appearances or even take up residency in the St. Croix. Our transmitters have a 10 year life expectancy, which is a really long time. But for a fish that can live for 100 years, monitoring 1/10th of the fish’s lifespan is still a relative snapshot.

What is the average age of sturgeon in the St. Croix?

I don’t know the average age of Lake Sturgeon in the St. Croix. The average age would skew to younger fish because there should be more younger fish than older fish. We have a hard enough time catching large numbers of any size fish, and the abundant smaller ones have not been sampled well at all.

I do have some aging data. There has been little agreement on sturgeon ages between independent readers. Some recent public recapture reports are helping to shed some light on the aging issues we have had. Generally, I assigned an older age for a given fish. As we are getting anglers catching tagged fish and reporting lengths, the fish appear to be lining up better with my older ages for fish at the reported size. But that is preliminary data that requires some further analysis.

How many harvest tags does the DNR issue per year?

From 2006-2019, an average of 3,123 harvest tags have been sold per year. 2019 had 3,784 tags sold and the highest ever sold was 4,164 in 2016. Those harvest tags are not site specific, so anglers can legally harvest a Lake Sturgeon during the open season in the St. Croix River, Rainy Lake, or the Rainy River/Lake of the Woods.

It seems like the popularity of sturgeon fishing has been growing steadily every year. Have there been any creel surveys done documenting angler participation and success?

No creel surveys have been done to specifically account for Lake Sturgeon on the St. Croix River. The last creel survey conducted on Lake St. Croix was from December, 2012 through October, 2013. During that time frame, the only legal time frame anglers could target Lake Sturgeon was the fall harvest and catch and release season in September through the first half of October. So sturgeon anglers would have little representation with the small six week season. Only 1.7% of the anglers interviewed during the open water creel survey in 2013 were targeting Lake Sturgeon. Now that the harvest and catch and release season is open for 8.5 months, I would expect a new creel survey to show much different targeted sturgeon effort, especially in the winter. No Lake Sturgeon angling was allowed in the winter of 2012-2013 and Lake Sturgeon ice fishing has exploded in popularity.

One problem with our creel surveys is that we don’t capture night anglers. There are a large number of sturgeon anglers that fish at night, both on open water and on the ice. So if we repeated our last creel survey, we would still probably under estimate our targeted Lake Sturgeon effort and success, just like we have done with catfish over the years.

What is the conservation outlook for sturgeon in the St. Croix?

I think the outlook is really good. As we continue to learn more about the St. Croix Lake Sturgeon population, it will not only benefit our knowledge of the St. Croix, but the connected waters like the Mississippi River. We have to see what the data tells us. There could be opportunities to expand the season, expand the harvest areas, or modify the harvest size.

Some anglers have expressed a desire to have a harvest slot on the St. Croix like they have on the Rainy River/Lake of the Woods. I’m not saying we are headed in that direction though. Again, it depends on what we can learn from the data over the next several years, listening to what anglers want or don’t want, and what is safe for the future of the fishery.

With fish that live to 100 years old and don’t mature until they are in their 20’s, we can’t afford to make any mistakes or it could set us back decades. So I would expect any changes, if they happen, would be conservative.

Ray Valley is an Aquatic Biologist with Navico Inc. and former DNR Fisheries Research Biologist. Ray lives in Bayport and is an avid Sturgeon angler.


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One response to “The travels of lake sturgeon”

  1. Troy Avatar
    Troy

    Very interesting article. I have witnessed two injured sturgeon with damaged notochords floating in the water below the St. Croix Fall dam over the years.

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The travels of lake sturgeon