Getting Antsy

Swimmers, take your mark… Lake Sturgeon in the Osage and Gasconade Rivers are on the starting blocks waiting to embark on their spring upstream migrations. A few fish in the Gasconade, may have already jumped the gun. On February 27th, a warm rain had the Gasconade out of its banks, and that was just enough to convince a few over eager sturgeon it was time to move.  Three fish moved began moving upstream as the water rose and traveled at least 9 miles from near the confluence with the Missouri River past Fredericksburg. Even in the Osage River Lake Sturgeon were stacking up in the heads of pools just upstream of their winter haunts seemingly antsy to get underway. Except the problem was that a few days later air temperatures and flows began to plummet with water temperatures dipping back under 50 degrees Fahrenheit. The fish responded by, pausing in the lower river. In many populations the first to arrive on the spawning grounds are the males. The females tend to hang back and arrive a few days later. The optimal spawning temperatures are from 52-60 F.

A muddy post-flood Gasconade River

During the cold spell, we switched to setting gill nets to capture and tag a few more staging Lake Sturgeon in the Gasconade. By the end of the week we had tagged 8 Lake Sturgeon bringing our total to 27 in the Gasconade and 93 overall. On the last day, we captured one of the plumpest Lakers we had ever seen. During surgery, developing eggs began bursting through the incision; eggs that that hopefully will be deposited on a rocky shoal sometime later this spring. Females only spawn ever 4-7 years. The year before the spawn the eggs will be yellow turning from gray to black by the next spring. The eggs told the story. She was almost ready. The eggs had a dark bullseye, the germinal vesicle which during development moves to the pole of the egg. Farmers who raise sturgeon for caviar production have often looked at the germinal vesicle to judge egg stage. It would still take a little time before they were ripe. Following fish like this throughout the spring migration will give us an idea where, if at all, the Lake Sturgeon are attempting to spawn. We are expecting some rain next week, and a slow warming could this be the time?

Me about to release the 40 lb female.
Eggs peeking through a surgery incision. The fish was sutured up and released unharmed.

Like the sturgeon, myself and most of my friends and coworkers are ready for spring as well. Going fishing when most of the ponds are too chilly to get a bite, starting to think about checking our favorite spot for morels. Our female sturgeon was a reminder to be patient. Spring will be here soon, and before we know it giving way to the oppressive heat of Missouri summer.

 

Citation

Bruch, R. M., and F. P. Binkowski. 2002. Spawning behavior of Lake Sturgeon (Acipenser fulvescens). Journal of Applied Ichthyology 18:570-579.

http://www.glsturgeon.fw.msu.edu/sturgeon/life-history/egg-stage

 

The Cold Shoulder

With rows of sharp scutes lining their body, Lake Sturgeon are a little rough around the edges, literally, but I can’t help but love them anyway. I also am afraid I am beginning to develop a common pathology of among scientists  where constant thought your study species, leads to concern about their well being. In the final stage of this condition, the scientist adopts a protectionist role. Let’s call it Mother Hen Syndrome. Each time I release a tagged sturgeon, I feel like the over anxious mother sending their child off on the bus on the first day of kindergarten. Will they be okay? Will the other sturgeon ostracize them for their stitches on their abdomen?

Complicating matters is the fact that, my tagged sturgeon have been giving me the cold shoulder. My running total of tagged Lake Sturgeon is 79 individuals in the Osage and Gasconade rivers. Over the more the 5,000 setline hook nights it took to capture these 79 sturgeon how many recaptures have I had? If you guessed zero, you would be correct.  Again I think of the mom who sends their kids off to college, “you never call!!”

Me being a “helicopter biologist.”

To a population ecologist, there are a couple explanations for low recaptures of marked organisms. First, there is a “trap effect” where the capture process causes an organism to avoid sampling gear in the future and therefore is less likely to be recaptured. And secondly, you have only managed to tag a small proportion of the population and thus are more likely to capture unmarked individuals than marked ones.  I don’t have an answer to explain the lack of recaptures I’ve seen and haven’t found conclusive evidence in the literature as well. I did come across a 2004 report from the Michigan Department of Natural Resources that reports below expectation recapture rates for fish captured in trawls, suggesting a behavioral avoidance of trawls. Although they didn’t notice as striking of a pattern for setline recaptures, it is certainly possible that a Lake Sturgeon might avoid the offering of a juicy earthworm after having been poked by a 8/0 hook once.  Using side-scan sonar, the report’s authors estimated that between 5,000 and 29,000 sturgeon use 1 square mile of habitat in the St. Clair River Delta. In our time on the river we have noticed lots of large bottom dwelling fish on sidescan sonar returns in areas where tagged lake sturgeon are hanging out. With the abundance of large fish species present in the Missouri River basin including Blue and Flathead Catfish or Paddlefish, it can be hard to know if large fish on sonar are definitely Sturgeon. I was reminded of the difficulty in estimating population size as I read the famous quote a colleague had pasted in his email signature “Managing fish is like managing trees, except they are invisible and they move.” The exact same applies to counting them.

Population estimates are beyond the scope of my project which is focused on habitat use and movement of Lake Sturgeon. Some day perhaps another graduate student will devise an ingenious study to answer these very questions in order to better assess the status of Lake Sturgeon in the Missouri River basin. And to all of the biologists out there, please share if you know of any studies addressing this or have anecdotal observations from your own sampling for Lake Sturgeon.

To end on a positive note, all signs point to the fact that my Sturgeon are thriving. They are behaving like a sturgeon should moving, hanging out in predictable habitats. A few weeks ago I even received an email from a biologist who had been contacted by an angler who had accidentally caught one of my tagged sturgeon while Sauger fishing. Updates like these are always soothing, nonetheless, their avoidance still gnaws at me a little bit. I miss my babies. Why the cold shoulder?

 

Literature

Thomas, M. V., and R. C. Haas. 2004. Abundance, Age Structure, and Spatial Distribution of Lake Sturgeon Acipenser fulvescens in the St. Clair System. State of Michigan Department of Natural Resources Report No. 2076.