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!!”
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?
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.