The phone rang late on a Saturday morning near the end of the 2013 CSRP sampling season. Crews that were out hoping to catch another female pallid sturgeon to implant and track were calling in with news. The weekend crew leader said, “It’s a reproductive male, should we tag it?” The 3.7 kg (8.2 lb) male pallid sturgeon was captured by CSRP biologists on trotlines set at river mile 177.2 near Boonville, Missouri. He was more than 70 river miles downstream from the closest reproductive female. Could he possibly swim upstream to reach one of the tagged females in time? The decision was made to tag him and take the chance. The epic story of PLS13-002 had begun.
Biologists were able to determine that PLS13-002 was originally produced in a hatchery by the presence of a coded wire tag, and that he was in reproductive condition by the use of noninvasive ultrasound techniques. After a quick ultrasound scan, PLS13-002 was surgically implanted with a telemetry transmitter and data storage tag, and was then released back into the Missouri River. Typically, fish are expected to rest after a surgery and do not display much movement in the days following a procedure. Therefore, CSRP biologists were quite surprised when they located PLS13-002 21 miles upstream just five days after his implantation.
Approximately one month later, CSRP biologists tracking one of this year’s females (see previous post Gang of Eight) were surprised when they detected PLS13-002 more than 200 miles upstream near Leavenworth, KS. There he was, at what biologists believed to be a spawning location. And he didn’t stop there. PLS13-002 traveled another 190 miles upstream where he reached his migration apex just above Plattsmouth, NE at river mile 593, near another tagged female. It is impossible to know how many spawning locations he may have visited and how many females he may have met along the way. With spawning season over and his journey at an end, PLS13-002 turned and began his downstream descent. Biologists located him again almost 490 miles downstream near Hermann, Missouri at river mile 105.6 by July 17, 2013.
During his springtime migration, PLS13-002 had traveled upstream over 415 miles at an average rate of 6.5 miles/day. Upstream and downstream migrations combined totaled almost 900 miles in a little over 3 months. Such long migrations are not an uncommon occurrence among pallid sturgeon tracked by CSRP biologists, but the precise strategy behind such migrations still remains something of a mystery. Did PLS13-002 have a predetermined destination in mind or did he simply keep swimming trying to find as many females as possible before the end of spawning season? Why do some male pallid sturgeon display such long migrations while others may only migrate 30 miles to reach their spawning locations? Are they seeking out the best spawning conditions or are they seeking females? These questions are fundamental to understanding how fish use the river and how the river can be managed to increase their populations.
Completed with contributions by Sabrina Davenport and Aaron DeLonay