A Most Unexpected Event

USGS biologists captured a single drifting free-embryo sturgeon in their nets while sampling the Lower Missouri River near the confluence with the Mississippi River on August 22, 2012 (see photo below).  The tiny sturgeon was barely a half of an inch long.  Based upon developmental characteristics, biologists determined that it hatched less than 5-7 days before it was captured.  This find was unexpected and somewhat puzzling as shovelnose and pallid sturgeon in the Lower Missouri typically spawn between April and June at water temperatures ranging from 60 to 72º F.

Why was this little sturgeon born in the middle of August at water temperatures exceeding 82º F, nearly two months after sturgeon should have stopped spawning?  Could this be natural variation in the population of sturgeon in the Missouri River or is it a sign that something unusual or unexpected is occurring?  Is it possible that this sturgeon embryo was spawned in the cool waters below the dams far upstream or in some shaded tributary and drifted down into the warm and muddy Missouri?  Have modifications to the Missouri River altered the timing of sturgeon spawning; extending the spawning season?  Or could one of our sturgeon species have more than one spawning strategy – are there spring spawning sturgeons and fall spawning sturgeons of the same species in the Missouri River?  This little enigmatic sturgeon has caused much speculation among the biologists who continue to sift the waters for drifting larval sturgeon.  Only time and continued sampling will help to unravel the puzzle.

A free-drifting sturgeon embryo was captured in the Lower Missouri River in late August. This was unexpected discovery as most sturgeon in the Lower Missouri River spawn in the spring.

By Aaron DeLonay



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