Drift and retention of sturgeon larvae

After sturgeon eggs hatch, the free-embryo larvae can drift as many as 17 days before “settling” into river habitats.  Previous analysis has indicated that if they drift at average water velocity in the river (4.5 – 7 miles per hour) they can be transported 100’s of miles downstream.  This means that many sturgeon larvae hatched in central Missouri would settle in the Mississippi River.  But it has also been hypothesized that under some hydraulic conditions larvae could be transported into marginal habitats along the river — eddies, backwaters, tributary mouths, low floodplain areas – where they will be retained, or at least slowed in their transit.

Hydroacoustic mapping boat R/V Lucien Brush mapping habitat during high water in the North Overton Bottoms Side-channel chute, Big Muddy National Fish and Wildlife Refuge.

This summer the USGS habitat team is working with the US Fish and Wildlife Service, Columbia Fisheries Office, to characterize some of these areas and the velocity patterns just upstream that could influence transport into them.  We are assessing potential retention habitats by mapping velocity patterns with an acoustic Doppler current profiler and bottom contours with a multi-beam depth sounder.   There is particular interest among river managers in the potential for larvae to be transported and retained in side channels that have been constructed for habitat restoration.  The depths and velocity patterns at inlets and outlets from side channels and at tributary confluences can be particularly complex because of complex flow around river-training structures (wing dikes).

Multibeam bathymetry (top) and current velocities (bottom) at the mouth of the Osage River mapped during high water June, 2011. Sturgeon telemetry positions (black squares) show concentrations in slow, deep water.

Young fish may also be retained in shallow-water habitat areas within the main channel, particularly if those areas are vegetated.   Flooded, vegetated areas have lower velocities and it has been hypothesized that they provide refuge from high velocities in the main channel and increased opportunities to young sturgeon to feed.

Flooded vegetation along the Missouri River, June 30, 2011. Flooded, low-lying, vegetated floodplains may provide refuge or food for young sturgeon.

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