For more than a week in early June, USGS telemetry tracking boats from Missouri joined the Montana Wildlife Fish and Parks and the USGS Fort Peck Field Office as they raced up and down the Yellowstone River trying to keep up with dozens of large, migrating pallid sturgeon. The biologists worked long hours collecting data on sturgeon movements and the pathways they travelled, all the while scratching their heads and speculating on why these sturgeon do what they do. Despite traveling hundreds of miles back and forth to document the spring spawning migration, tracking crews continually returned to a few bends of the Yellowstone River downstream of Fairview, Montana. Over the first few weeks of June, loose aggregations of up to a dozen telemetry-tagged, male pallid sturgeon were located near the site, a few miles upstream from the Missouri River confluence. The typical sing-song chirp of a single telemetry tag usually heard from the receiver’s speaker was replaced by what sounded like a swarm of angry crickets as the tracking boats approached the site. The biologists needed to know, why they were there, what are they doing, and what are they waiting for?
USGS boats surveyed the area with sidescan and DIDSON sonar to try and determine what the sturgeon might be doing and how closely they were interacting. Sonar data showed that the males did not sit idly, but moved actively around the site. Were they just feeding in the area, or were they waiting for a female to show up and spawn? The only way to know for sure was to attempt to recapture some of the males. If examination of the males revealed that they were ready to spawn, then the chances were good that the males had selected the spawning site and were just waiting on the females to arrive.
Biologists targeted the aggregation of male pallid sturgeon with drifted trammel nets on Thursday, July 14. Three large male pallid sturgeon were caught in the weighted net as it dragged along the river bottom. It took only minutes for USGS biologists to scan each sturgeon with a portable ultrasound device and determine that all three were “ripe” and ready to spawn. Now that the biologists knew that the males were ready, it was their turn to wait.
By Aaron DeLonay