PLS11-016, PLS11-017, PLS11-018, and PLS11-020 are all female pallid sturgeon from our upper  study segment.  They were released in reproductive condition from the pallid sturgeon conservation augmentation program during spring 2011, but that is where the similarities end.  Females PLS11-016, PLS11-017, and PLS11-020 were not intensively tracked during spring 2011; fortunately each of these fish were also implanted with data storage tags (DST) which record depth and temperature at 15 to 30 minute intervals.  These data allow us to examine behavior of individuals during periods that we would otherwise be unable to document and, in this case, give some indication of spawning location.  By comparing  various temperature data between the Platte and Missouri Rivers we were able to infer that PLS11-016 and PLS11-020 likely spawned in the Platte River, while PLS11-017 spawned somewhere in the mainstem of the Missouri River (see previous blog entry “Where Are You When I’m Not Looking?”).   PLS11-018, on the other hand, was intensively tracked but exhibited limited reproductive behavior, remaining relatively stationary for more than a month.  During June 2011, biologists targeted PLS11-018 for reproductive evaluation, which revealed that she had failed to spawn.  When female sturgeon fail to spawn, their black or dark grey eggs begin to break down and are slowly reabsorbed.  Two years later all four are ready to spawn again.

The four reproductive pallid sturgeon downstream in our lower study segment have little in common.  Female pallid sturgeon PLS11-004 was initially captured and implanted during March 2011 in non-reproductive condition.  In the fall of 2012 she was targeted for recapture when she moved more than 100 miles upstream.  Ultrasound evaluation to revealed that the developing eggs in her ovaries had progressed to the point where she would likely attempt to spawn during spring 2013.  PLS08-035 is a female pallid sturgeon initially implanted during May 2008 in after being artificially spawned at Blind Pony State Fish Hatchery as part of the population augmentation program.  During the nearly five years of subsequent observations in the Missouri River she has been recaptured and her reproductive condition re-evaluated during 2010, 2011, and again in 2012.  For the first four years she remained non-reproductive and relatively stationary.  That is, until October 2012, when ultrasound examination revealed that she would likely be ready to spawn during spring 2013.  Two new fish in reproductive condition joined the Comprehensive Sturgeon Research Project in spring of 2013, PLS13-001 and PLS13-002, rounding out the Gang.  PLS13-001 is a hatchery-reared, female pallid sturgeon initially captured and implanted April 2013.  Biologists were able to readily identify this fish was of hatchery origin by the presence of numerous tags including visual implant elastomer and coded wire.  Male pallid sturgeon PLS13-002 was initially captured and implanted during April 2013.  Since implantation PLS13-002 has moved more than 40 miles upstream.

While each indivual fish is different with its own unique history, they each have the same common goal, to migrate to a suitable spawning location, find a mate, and reproduce.  Biologists are hoping that this Gang of Eight will collaborate to reveal important new information on the reproductive ecology of the pallid sturgeon.

Figure 1. A map showing the most recent telemetry locations of reproductive pallid sturgeon during 2013.

Check out the Missouri Department of Conservation’s Lake Sturgeon webpage to learn more about the State’s efforts to recover the “other” Missouri River sturgeon.  And if you happen to be out on the Missouri or Mississippi River, or one of their tributaries and you are fortunate to catch a large lake sturgeon, your local Missouri Conservation Department office would like to hear about it.

Photo 1. A USGS Biologist holds a juvenile lake sturgeon caught on a trotline while sampling for pallid sturgeon. The young lake sturgeon had a PIT tag that identified it as a fish previously captured and released by the Missouri Department of Conservation.

Photo 2. Compared to the pale, slender pallid sturgeon, the dark brown or olive grey lake sturgeon has a stocky build and a conical shaped snout. It is commonly referred to as a “rubbernose” sturgeon.

By Aaron DeLonay

Mean discharge and temperature of the Missouri River near Hermann, MO. The dashed bars represent the approximate threshold for pallid sturgeon spawning. In 2012, spawning temperatures were reached in March. Previous spawning events typically have occurred later in the springtime, from late April to early May.

Completed with contributions by Kimberly Chojnacki and Jake Faulkner

At the end of the day the biologists netted their fish.  PLS11-010 was weighed and measured, and the tags she had carried for the last two years were replaced with new ones supplied with fresh batteries.  The oocytes (developing eggs) inside her smooth abdomen are small and white, meaning she will not be ready to spawn this spring.  Maybe next year will be her year.

Ring-billed gulls line a sand bar along the Missouri River to watch USGS boats fish for sturgeon.

A wild turkey perches on a rock dike in the Missouri River to get a closer look at USGS boats fishing for sturgeon.

By Aaron DeLonay

The extreme temperatures and drought have had noticeable impacts on the Missouri River. In March of 2012 water temperatures in the Lower Missouri warmed  quickly, reaching spawning temperatures for many fish species far earlier than usual.  The following month, Comprehensive Sturgeon Research Project (CSRP) biologists documented a pallid sturgeon spawning event that was approximately four to six weeks early compared to previous spawning events (See previous posts “Rising Temperature” and “An Early Spawning Record”).  Drought conditions have continued and resulted in low river levels into 2013. Unusually low river conditions  have the potential to create hazardous situations for our tracking boats through the winter including exposed sand bars and rock formations, ice flows, and unusable boat ramps.  With this in mind, CSRP biologists have been making extra efforts to ensure crew safety by monitoring river and weather conditions, closely.

The drought conditions that affect the Missouri River Basin will likely persist through winter and into spring, but CSRP biologists will be ready for whatever the weather brings.

January 2013: CSRP biologists traveled along the Missouri and Mississippi rivers in search of usable boat ramps from which to launch their tracking boats. Pictured is a ramp located on the Mississippi River near Cape Girardeau, MO.

January 2013: CSRP biologists traveled along the Missouri and Mississippi rivers in search of usable boat ramps. Pictured is a ramp on the Mississippi River near Grand Tower, IL. The photographer is standing at the river’s edge, looking up the boat ramp, from far below where boats are normally launched.

Pallid sturgeon PLS10-017 was originally implanted with telemetry devices in the spring of 2010 as a non-reproductive female.  In June of 2012, this female was recaptured and reimplanted with telemetry devices with fresh batteries at river mile (RM) 543.7 near Peru, Nebraska (for more information on data storage tags see the previous post “Where Are You When I’m Not Looking?”).  At that time, she had small, white-gray eggs that were visible in the ultrasound and through the small incision made during surgery.  Field crews hope to recapture PLS10-017 this fall to determine if her eggs have developed to the point where they can confidently predict that she will likely spawn in the spring of 2013.  PLS10-017 was last located at RM 554.9 during August’s river sweep.

Female pallid sturgeon PLS11-018 was originally captured, implanted with telemetry devices, and released near river mile 185 during the spring of 2011.  Since then, tracking crews have located her on 25 different occasions throughout the Missouri River.  PLS11-018 was found at RM 341.9 in late March of 2012 and was last located at RM 602.6 near the end of September.  This steady upstream movement could indicate that PLS11-018 may be getting an early start on a spring spawning migration.  Similar to PLS11-018, female pallid sturgeon PLS08-035 has been moving up the Missouri River.  From her initial capture date in 2008 through January 2012, this female has moved only 2.5 miles.  Starting in May of 2012, PLS08-035 has moved upstream approximately 85 miles.  Could she also be getting a head start on a spring spawning migration?  Biologists will be targeting these females this fall to find out.

Telemetry locations of two female pallid sturgeon: PLS11-018 (top) and PLS08-035 (bottom). The steady upstream movement displayed by both fish may indicate an early start to spring spawning migrations.

Why was this little sturgeon born in the middle of August at water temperatures exceeding 82º F, nearly two months after sturgeon should have stopped spawning?  Could this be natural variation in the population of sturgeon in the Missouri River or is it a sign that something unusual or unexpected is occurring?  Is it possible that this sturgeon embryo was spawned in the cool waters below the dams far upstream or in some shaded tributary and drifted down into the warm and muddy Missouri?  Have modifications to the Missouri River altered the timing of sturgeon spawning; extending the spawning season?  Or could one of our sturgeon species have more than one spawning strategy – are there spring spawning sturgeons and fall spawning sturgeons of the same species in the Missouri River?  This little enigmatic sturgeon has caused much speculation among the biologists who continue to sift the waters for drifting larval sturgeon.  Only time and continued sampling will help to unravel the puzzle.

A free-drifting sturgeon embryo was captured in the Lower Missouri River in late August. This was unexpected discovery as most sturgeon in the Lower Missouri River spawn in the spring.

By Aaron DeLonay