U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2007–3053

July 2007

Sturgeon Research Update: Confirmed Pallid Sturgeon 

Spawning in the Missouri River in 2007

The U.S. Geological Survey (USGS) 

in partnership with the Nebraska Game 

and Parks Commission (NGPC) and 

the U.S. Army Corps of Engineers have 

confirmed spawning of two female pallid sturgeon in the upstream reaches of 

the lower Missouri River in May 2007. 

Combined with supporting research in 

reproductive physiology, identification 

of spawning habitat, and early life history 

this result provides new understanding 

of environmental factors (for example, 

photoperiod, temperature, water quality, 

and flow regime) that might affect reproduction of this endangered species. The 

purpose of this fact sheet is to provide 

stakeholders, scientists, and managers 

with some of the preliminary results from 

the 2007 field assessment of sturgeon 

reproduction in the lower Missouri River.

Background on Sturgeon Research

The USGS and NGPC are involved 

in a multi-year, collaborative research 

study to determine factors leading to 

spawning and survival of the endangered 

pallid sturgeon and the closely related 

shovelnose sturgeon. During spring 2007 

researchers tracked the movements of 195 

sturgeon between Omaha, Nebraska, and 

Gavins Point Dam, South Dakota (fig. 1). 

The purpose of the study is to determine 

how sturgeon reproduction is affected 

by river flow and habitat availability.

The research is set up as a series of 

field experiments in which sturgeon 

are tagged with combined acoustic 

and radio transmitters (CART) that 

allow scientists to follow their movements along the river. Physiological 

measurements were used to determine 

the spawning potential of each fish. 

Habitats used by the fish are to be 

related to available habitats to predict 

areas selected for spawning.

2007 Field Experiment

The 2007 sturgeon field assessment was intended to document 

sturgeon reproductive behavior and 

habitat availability under conditions 

of no flow modification from Gavins 

Point Dam. Results from this assessment will be compared to those of 

the limited pulse-flow modification 

(“spring rise”) of 2006. Results from 

subsequent years with and without 

flow modification will be needed for 

validation.

Discharges from Gavins Point Dam 

were maintained at low levels during 

March to mid-May 2007 because of 

continuing drought in the upper basin, 

spring flooding downstream in Iowa 

and Missouri, and lack of navigation 

traffic to Sioux City, Iowa. Cycling 

flows were initiated by the U.S. 

Army Corps of Engineers on May 18, 

2007, to control elevations at which 

interior least terns and piping plovers 

nest on sandbars in the unchannelized segment of the river. Flows were 

stabilized at 18,000 cubic feet per 

second on June 3, 2007. Although 

releases from Gavins Point Dam were 

relatively low from March through 

mid-May, runoff from the James, Vermillion, and Big Sioux River Basins 

provided a series of unplanned flow 

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Figure 1.  Study area for 2007 field assessment of sturgeon reproduction, Lower Missouri River.

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EXPLANATION

Pallid Sturgeon 541

Pallid Sturgeon 561

River Segments

Gavins Point to Ponca

Ponca to Sioux City

Channelized downstream from Sioux City

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pulses that are reflected in the USGS 

Sioux City streamflow-gaging station 

record (fig. 2).

The variable hydrology was distributed among three geomorphically 

distinct river segments (fig. 1). From 

Gavins Point Dam (river mile 811) to 

Ponca State Park (river mile 753.5), 

the river is characterized by complex 

reaches with dynamic sandbars, multiple 

channels, and islands. From Ponca State 

Park to Sioux City, Iowa (river mile 

734), the river channel is transitional to 

the engineered, navigation channel. This 

reach has been narrowed and stabilized 

with bank revetment and some wing 

dikes, but maintains some mid-channel sandbars and channel complexity. 

Downstream from Sioux City, the river 

has been channelized for navigation and 

is mostly a single-thread channel with 

rare mid-channel sand bars. 

Variable hydrology and morphology 

of the mainstem Missouri River and 

tributaries resulted in a range of potential interactions between environmental 

cues and habitat availability for sturgeon 

during spring 2007. Although it will be 

challenging to isolate which factors had 

the greatest affect on sturgeon spawning, 

the large number of tagged fish in this 

field assessment will provide an extensive dataset for analysis.

Preliminary Results from 2007

In March and April 2007, 8 pallid and 

176 shovelnose sturgeon were surgically 

implanted with CART series transmitters 

that permitted researchers to track their 

movements in the river. The fish also 

were implanted with archival data storage tags (DST’s) that record depth and 

temperature (fig. 3). The reproductive 

condition of each fish was determined 

through ultrasonic and endoscopic 

examination and by visual examination of the gonads during implantation. 

Of the pallid sturgeon implanted, two 

females and three males were in reproductive condition and expected to spawn 

during 2007. Another 11 pallid sturgeon 

that had been implanted previously with 

transmitters in 2006 also were tracked 

within and below this river reach. The 

reproductive readiness to spawn was 

assessed for each female pallid and 

shovelnose sturgeon at the time of 

implantation using the egg polarization 

index measurement, which is an indication of how soon a female will spawn; 

the egg polarization index decreases 

as the time of spawning draws near. A 

polarization index value of 0.07 or less 

indicates that spawning is imminent. 

Additional shovelnose sturgeon were 

captured weekly throughout the spring 

to monitor when the sturgeon population 

within these river segments would be 

physiologically capable of spawning.

Intensive tracking efforts were initiated in April on the two female pallid 

sturgeon in reproductive condition. In 

early May, based on water temperature 

and behavioral movements, 24 hour continuous tracking efforts were initiated. 

Two boats operated by NGPC conducted 

40,000

30,000

20,000

10,000

0

2/24

DISCHARGE,

IN CUBIC FEET PER SECOND

WATER TEMPERATURE,

IN DEGREES CELSIUS

3/16 4/5 4/25 5/15 6/4

2007

 Gavins Point Dam

Sioux City

2006

 Gavins Point Dam

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20

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10

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2006 Flow Modification

2007

Sioux City

Figure 2. Hydrograph and water temperature showing variation of Missouri River environmental

conditions during March through May 2007.

Figure 3. Pallid sturgeon PLS07-004

(acoustic tag 541) after recapture (above)

and data storage tag and combined

acoustic radio transmitter (right). Photographs by Aaron DeLonay, U.S. Geological Survey.
the intensive tracking efforts. The USGS 

conducted extensive river tracking 

efforts for all tagged sturgeon and served 

as reserve vessels for the intensive pallid 

sturgeon tracking efforts. Field crews 

from the NGPC and USGS relocated 

each reproductive female pallid sturgeon more than 100 times in a 2-month 

interval before attempting to recapture 

them to determine if they had spawned 

(fig. 4).

Both female pallid sturgeon showed 

intervals of rapid upstream movement, 

followed by intervals of slower downstream movement with extended pauses. 

This characteristic movement pattern 

was noted by the USGS in an earlier 

phase of this study in 2005 and 2006. 

The earlier study focused on spawning 

individuals of the closely related shovelnose sturgeon. We infer that spawning 

generally occurs at the upstream apex of 

these movements. The USGS and NGPC 

recovered the two telemetry-tagged pallid sturgeon females from the Missouri 

River. USGS researchers re-examined 

each female with ultrasound and an 

endoscope in the field to determine if 

spawning occurred. After a positive 

indication from the non-invasive methods, a small surgical incision was made 

to visually examine the gonads and to 

retrieve the DST tags from the abdominal cavity.

Both female pallid sturgeon were 

determined to have spawned completely. 

The first female, captured on March 26, 

2007, at river mile 659.7 with an egg 

polarization index of 0.17, moved 109.1 

river miles upstream before spawning 

upstream from Ponca State Park within 

the Missouri National Recreational 

River segment, probably in mid-May. 

It was recaptured after moving downstream to river mile 756.5 on May 23, 

2007 (fig. 4). The second female was 

captured on March 29, 2007, at river 

mile 650.3 with an egg polarization 

index of 0.12, and moved nearly 50 

miles upstream from the implantation 

location before spawning in the channelized reach downstream from Sioux 

City, Iowa (river mile 734), probably in 

late April to early May. This fish was 

recaptured on May 25, 2007, at river 

mile 676.7 after moving downstream. 

Both fish were in good overall physical 

condition upon recovery.

This is the first direct evidence that 

pallid sturgeon spawn in the Missouri 

National Recreational River segment 

and in the channelized river upstream 

from the Platte River. The DST data, in 

combination with telemetry relocations, 

are the first complete records of pallid 

sturgeon that migrated and spawned. 

Analysis of depth data recorded by DST 

tags also indicates a characteristic pattern of behavior that may be associated 

with spawning. Whereas researchers 

successfully documented spawning, this 

study does not reveal whether or not 

spawning occurred under optimal conditions, or whether or not enough eggs 

hatched or young survived to add to the 

pallid sturgeon population. Although 

spawning occurred in 2007 without flow 

modification from Gavins Point Dam, 

fish may have responded to natural 

spring pulses from tributaries. Data from 

pallid sturgeon will be compared with 

observations on shovelnose sturgeon to 

assess spawning and characterize reproductive strategies of the two species.

Additional Research 

Accomplishments

In addition to the results summarized 

above, the 2007 research efforts have 

yielded additional accomplishments:

• Observations of movement and 

habitat use by pallid sturgeon 

and shovelnose sturgeon indicate 

that spawning occurs during an 

extended time at multiple locations within the study segments. 

Female reproductive movement 

seems to be characterized in both 

species by a significant and rapid 

upstream movement, followed by 

sporadic downstream movement. 

Movement patterns of reproductive male sturgeon appear to be 

more complex. Data indicate that 

some reproductive male pallid and 

shovelnose sturgeon show more 

diverse movement patterns during 

the spawning.

• Telemetry data document that 

reproductive and non-reproductive shovelnose sturgeon used the 

mainstem and some tributaries to 

the Missouri River before, during, 

and after spawning. In contrast, 

pallid sturgeon used only mainstem 

Missouri River habitat or areas 

near tributary confluences. None of 

the 5 tagged pallid sturgeon have 

been observed in Missouri River 

tributaries. 

• Hydrologists mapped 10 highprobability spawning reaches as 

determined from fish tracking data. 

Maps include depth, velocity, and 

substrate distributions that will 

be analyzed to delineate physical 

factors that contribute to sturgeon 

reproduction.

Figure 4.  Relocation events for female pallid sturgeon PLS07-004 (acoustic tag 541, fig. 3).

2007

03/26 04/09 04/23 05/07 05/21 06/04 06/18

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Relocation events

Recapture location

RIVER MILE
• Water-quality monitors at multiple 

USGS streamflow-gaging stations 

along the river recorded changes in 

temperature, pH, turbidity, and dissolved oxygen as they varied with 

discharge. These water-quality 

changes will be analyzed to assess 

their roles as cues in spawning 

behavior.

• Research biologists with the USGS 

and the South Dakota Game, Fish, 

and Parks have been sampling the 

Missouri River area below Gavins 

Point Dam for eggs and larval 

sturgeon using fine meshed nets. 

Once these samples are analyzed, 

additional verification may be 

obtained that sturgeon spawned and 

eggs hatched in that area.

Michael Mac, Director

U.S. Geological Survey

Columbia Environmental Research Center

4200 New Haven Road

Columbia, Missouri 65201

Phone: 573-876-1900

Email: mmac@usgs.gov

Gerald Mestl

Nebraska Game and Parks Commission

2200 North 33rd Street

Lincoln, Nebraska 68503

Phone: 402-471-1512

Email: gerald.mestl@ngpc.ne.gov

For more information contact: 

Channelized segment of the Missouri River (river mile 707.5) downstream from

Sioux City, Iowa, in late May to early June, 2007 (photograph by Joanna Reuter,

U.S. Geological Survey).