We’ve Only Just Begun

After a long, cold winter, the Redbud and Dogwood trees are blooming and water temperatures are rising (Figure 1).  Spring seems to have finally sprung, and fish, and hopefully the endangered pallid sturgeon among them, will soon be spawning.  In an effort to better understand pallid sturgeon spawning, fertilization, hatch, and dispersal, Comprehensive Sturgeon Research Project (CSRP) biologists initiated weekly sampling efforts for Acipenseriformes (sturgeon and paddlefish) free embryos on April 15.  The work is occurring at two sites in Nebraska; one upstream of the confluence of the Missouri and Platte rivers (near river mile 600) and the other is located less than one mile up the Platte River.

Figure 1. Temperature and discharge of the Missouri River at U.S. Geological Survey streamgage 06601200 Decatur, Nebraska.

 In order to sample the swift waters for Acipenseriformes free embryos, CSRP researchers deploy a pair of very fine, cone shaped ichthyoplankton sampling nets attached to 100 pound lead weights into the water column using winches mounted to each side of an anchored boat.  The nets filter water through a 0.5 meter opening and the drifting embryos are captured by the nets.  The nets must be made with a very fine mesh (0.75 mm) to prevent the small tadpole-like larvae (7-8 mm) from slipping through.  

The sampling nets are simultaneously brought back up (Figure 2) to the surface after a set period of time (5 to 15 minutes, depending on the debris load suspended in the water column).  The contents of the sapling nets are emptied into pans, where Acipenseriformes free embyros are hand-picked from the debris.  Recently hatched sturgeon and paddlefish free embryos are too small and similar to differentiate, so they are preserved in alcohol and returned to the laboratory where they will be identified to genus using a microscope.  Sturgeon specimens will be sent to a genetics laboratory to determine if they are shovelnose sturgeon, or if we are very lucky, the endangered pallid sturgeon.  We haven’t caught any Acipenseriformes free embryos to date (April 30), but spawning season is just beginning.

Figure 2. Biologists sample the water column of the Missouri and Platte Rivers to collect sturgeon or paddlefish free embryos).

With contributions by Aaron DeLonay

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