Late last week, reproductive female PLS11-008 stopped her upstream migration and moved over to an outside bend of the river near Arrow Rock, Missouri. From our experience tracking female pallid sturgeon, we have come to recognize this as likely spawning behavior. Unfortunately for crews trying to observe such behavior, she selected deep, swift water over rock or bedrock. Water depths of 8 to 12 meters (26 to 39 feet) and current velocities exceeding 2 meters per second (roughly 4.5 miles per hour) at this site make it incredibly difficult to recapture adult fish, or to collect eggs or larvae. Although we have yet to recapture female PLS11-008 to confirm that she did spawn, we have to assume that she was spawning at this spot. We made the decision to “Go.” We dispatched boats and crews to characterize the habitat and sample for her offspring.
Two boats were dispatched to characterize the habitat. One boat made high-resolution maps of the depths and velocities in and around the site. Another boat deployed the “sand cam” (see previous post about the sand cam for more details) to get detailed photographic images of the substrate at the bottom of the river.
An additional cabin boat outfitted with acoustic cameras collected moving images of fish behavior (see previous post highlighting DIDSON use on the Osage River) as well as still images of the habitat where PLS11-008 was located on previous days.
An open workboat sampled for hatching sturgeon larvae. The capture and genetic matching of larvae to PLS11-008 would validate spawning, fertilization, and hatch at this site.
When PLS11-008 moves into somewhat shallower water, crews will attempt to recapture her. Evaluation will include confirming whether she actually spawned, downloading data from her data storage tag, and re-implanting a fresh acoustic tag with new batteries.
We’ve only been able to assess about a dozen pallid sturgeon spawning sites on the Lower Missouri River over the last several years, so each site contributes significant new information about the potential role of spawning habitat limiting reproduction. If the fish and the river cooperate this year, we’ll have additional spawning sites to assess upstream of Omaha, as well as in the Yellowstone and Upper Missouri Rivers in Montana.