During the first week of November, four adult pallid sturgeon with telemetry tags were recaptured by field crews using drifted trammel nets. It was a very good week. Field crews sent the data from each recapture back to the USGS Columbia Environmental Research Center (CERC) and the Sturgeon Information Management System was updated. This added more information to the continuing story of each sturgeon. Each sturgeon is an individual, but from the collection of many individual stories patterns begin to emerge. Sometimes the patterns are predictable. Sometimes we are surprised.
Female pallid sturgeon PLS11-014 was implanted and released into the Missouri River at river mile 591.5, near the Platte River in Nebraska on April 28, 2011. She was assessed as being in reproductive condition at that time with tightly packed grey eggs. On October 31, six months after implantation, PLS11-014 was successfully recaptured by CERC crews with drifted trammel nets at river mile 542.2. Reproductive assessments conducted at recapture indicate that she spawned this year. Unfortunately, we were tracking other females elsewhere, and were not there to document spawning when it occurred.
Female pallid sturgeon PLS11-015 was also implanted and released on April 28, and at the same location as PLS11-014. She, too was in reproductive condition and ready to spawn. By late October, PLS11-015 had also moved downstream over 40 miles. On November 1, she was recaptured and determined to also have completely spawned. Our crews were again tracking other females at the time and we did not locate her spawning site.
Although research crews could not track either PLS11-014 or PLS11-015 during the spring spawning period, they could determine from the condition of their ovaries that they had spawned. In addition, research crews recovered the data storage tags that each female carried. From this data we can determine the depths and temperatures the female sturgeon used during the spawning season, and during the flood that followed. Even when researchers cannot follow the fish, we can still collect data, and gain valuable insight.
Typically an adult female pallid sturgeon will lose about 10-20 percent (or more) of her body weight during spawning when she releases the thousands of eggs she carries. Even though PLS11-014 and PLS11-015 both spawned and released their eggs, each had regained the weight lost during spawning in less than six months. Similarly, female pallid sturgeon PLS11-012 was implanted and released in the Missouri River on April 6, 2011. She was non-reproductive at the time and weighted 3,120 g. She spent her summer near the mouth of the Platte River. After six months, she was recaptured on November 3. Although she was still not reproductive she weighed in at 4,330 grams. That is an increase in weight of 39 percent in only six months. Such rapid weight gain was unexpected. We hope to recapture more of our tagged adults to determine if this rate of weight gain was typical of pallid sturgeon in the Missouri River during 2011.
Finally female pallid sturgeon PLS09-011 was recaptured on November 1, 2011 at river mile 563.9. She was first implanted and released in September 2009 after being spawned in the hatchery that spring. Since then she has moved little, spending most of her time within five miles of river. When she was recaptured this November our record show that her weight had increased by 52% and she was once again gravid. She will spawn again in 2012, three years after spawning at Gavins Point National Fish Hatchery. Female sturgeon do not spawn every year. How frequently they spawn can provide insight into the quality of habitat in the river, and the potential for the population to increase with time.
It was a very good week.
By Aaron DeLonay