By Aaron DeLonay, Kimberly Chojnacki and Robert Jacobson
Three free embryos that were collected by Comprehensive Sturgeon Research Project scientists in May 2014 were recently confirmed to be pallid sturgeon. The three specimens were among several hundred paddlefish and closely-related shovelnose sturgeon collected from the Lower Missouri River immediately upstream of the confluence with the Platte River in Nebraska during 2014 (see previous entries, We’ve Only Just Begun and One Down, Several To Go). All three pallid sturgeon free embryos were collected from the main channel of the Missouri River on May 30, 2014. The specimens ranged in length from 9.59 to 10.42 mm, and were estimated to be between 1 to 3 days old based upon the developmental stage of the specimens and ambient river temperatures.
Pallid sturgeon hatch and disperse downstream from the spawning location as free embryos (figures 1 and 2). Free embryos lack a well-developed mouth, eyes or fins, and rely a large yolk sac to fuel their rapid development as they drift downstream with the current (see previous entry, A Change Will Do You Good). After 11-17 days these free embryos develop into larvae (figure 3) that settle to the bottom of the river and begin feeding.
The pallid sturgeon free embryos collected during 2014 were positively identified using genetic analyses developed by Jennifer Eichelberger and Dr. Edward Heist at Southern Illinois University Carbondale. Recent developments by Dr. Heist have resulted in genetic tests that use inexpensive Single Nucleotide Polymorphisms (SNP) assays to screen hundreds of specimens of sturgeon and paddlefish to identify possible pallid sturgeon embryos and larvae. Positive confirmation of the genetic identity of pallid sturgeon specimens is then determined using microsatellite DNA markers developed at SIU. Microsatellite markers are also used to determine whether sturgeon free embryos collected in samples may be closely related, or possibly siblings from a single spawning event. Preliminary analyses suggest that the three specimens are not siblings from a single spawning female.
These new genetic identifications add to mounting evidence that critically endangered pallid sturgeon spawned successfully in the Lower Missouri River downstream of Gavins Point Dam, South Dakota during 2014. These findings build on previous year’s effort by the USGS, Nebraska Game and Parks Commission, and U.S. Army Corps of Engineers to track the reproductive migration and behavior of pallid sturgeon, and to locate and describe functional spawning habitat in the Lower Missouri River. While successful spawning by the endangered fish was detected in the Lower Missouri River in 2014, it does not necessarily mean that the species is on its way to recovery. During this study, USGS scientists and their collaborators have been able to track adults on their migrations to their spawning sites, describe their spawning behavior, and characterize the habitats they use in the Lower Missouri River. Until 2014, scientists were unable to locate fertilized eggs or newly hatched embryos and larvae of pallid sturgeon, and therefore were unable to assess whether or where spawning by adults was successful. These new findings indicate that suitable conditions and functional spawning habitats for pallid sturgeon do at times exist in the Lower Missouri River downstream of Gavins Point Dam, however pallid sturgeon populations remain small and successful reproduction and recruitment to the population is still quite limited.