The Cold Never Bothered Us Anyway

Early this March, USGS Comprehensive Sturgeon Research Program (CSPR) biologists coordinated and led a pallid sturgeon surgery training effort in Dakota City, Nebraska for the U.S. Fish and Wildlife Service (USFWS) and the Missouri Department of Conservation (MDC).  Scientists from the three agencies endured bitter conditions with 20–30 mph wind gusts and wind chills below freezing to complete the training under field conditions on the bank of the Missouri River.  The USFWS brought five pallid sturgeon from the USFWS Gavins Point National Fish Hatchery.  The sturgeon had originally been captured for the use of broodstock but were later determined to be of hatchery origin and unsuitable for propagation.  The five sturgeon, two males and three females, were designated to be released back into the river with telemetry transmitters.  This made them perfect candidates for training new sturgeon surgeons.  Training included minimally invasive reproductive assessment with ultrasound, blood sampling for measurement of reproductive hormones, and surgical implantation with transmitters and archival data storage tags (DST).

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Training began by performing an ultrasound on each fish to determine the sex and reproductive readiness. The ultrasound allows a preliminary assessment of each sturgeon’s testes or ovaries to determine if they may be ready to spawn.  Following the ultrasound, 3.5 milliliters of blood were drawn from each fish and centrifuged in order to separate the blood platelets and plasma. The blood plasma will be frozen and stored for later measurement of sex steroids that provide additional information on sex and reproductive status.  The final procedure of the training was the surgical implantation of each sturgeon.  A 24–30 mm incision is made on the ventral surface of the abdomen with a surgical scalpel.  The surgeon visibly determines the sex of the sturgeon and notes the condition of the ovaries and testes, and the presence of visceral and gonad fat deposits.  An acoustic transmitter and DST tag are inserted through the ventral incision and the opening is closed with 3–4 sutures.  Acoustic transmitters allow CSRP biologists and scientists of other agencies to monitor the sturgeon’s movement while archival tags record the depth and temperature of the water wherever the sturgeon goes. Each surgery is completed in 10–15 minutes.  Upon completion of the surgical training, all sturgeon were transported in an aerated tank by truck to the river access closest to the point of their original capture on the Missouri River.  All sturgeon were released within hours of the procedures.  Two males and two females were released at the Dakota City access in Nebraska, and one female was released at the Blencoe access in Iowa.

All five pallid sturgeon brought from Gavins Point for surgery were in excellent health, condition, and had notable fat concentrations.  All three females were determined to be reproductively immature without visible maturing ova (eggs) and are not expected to spawn this year.  One of the males was also immature and not likely to be in spawning condition.  The second male had testes that were thickening with prominent lobes developing indicating that it is entering its pre-spawning stage.  Biologists will watch it closely to see if it finds other reproductive tagged sturgeon during the spawning season.