1. Use Distribution of Adult Pallid Sturgeon Scaphirhynchus albus in the Missouri River Below Gavins Point Dam J. David Adams 1, Ryan L. Ruskamp 1, Casey L. Bergthold 1, Kimberly A. Chojnacki 2, Aaron J. DeLonay 2 and Gerald E. Mestl 1 1 Nebraska Game and Parks Commission, 2200 N 33 rd St., Lincoln, NE 68503 2 U.S. Geological Survey, Columbia Environmental Research Center, 4200 New Haven Road, Columbia, MO 65201 Funding provided by the United States Army Corps of Engineers Introduction: The Nebraska Game and Parks Commission (NGPC) and the U.S. Geological Survey (USGS) are conducting a cooperative research project to study the behavior of pallid sturgeon in the lower Missouri River. One goal of this project is to quantify the spatial-use requirements and longitudinal movements of pallid sturgeon. The overall objective is to begin to understand how much river a pallid sturgeon uses in a given year. Also, we want to determine what variables, if any, affect this use distribution. Comparing use distributions between spawning and non-spawning adults, as well as comparing males to females will help us add to our understanding of pallid sturgeon behavior. Until very recently, most of what is known about pallid sturgeon has been inferred from knowledge of other sturgeon species. For this study, we have employed a large-scale telemetry effort where data are collected from adult pallid sturgeon that are implanted with acoustic transmitters. The locations of these fish are monitored extensively throughout the year as weather permits. The period of time during which tracking is possible normally extends from mid-February until late November or early December. Study Area: Adult human holding adult pallid sturgeon. Methods: Adult pallid sturgeon included in this study were surgically implanted with Lotek sonar acoustic tags. The battery life for the tags ranged from 1 to 2 years. Once the tag for any individual was believed to be running out of battery life, attempts were made to recover that fish by finding it’s exact location and drifting trammel nets over the spot in order to catch the individual. When a fish was successfully recaptured, it was reimplanted with a new tag. Fish were located by boat using Lotek SRX 600 and MAP 600 RT receivers coupled with submerged hydrophones. Each location was then mapped using ArcGIS and ArcPad software. Figure 2. The Missouri River from Gavin's Point Dam (river mile 811) to the mouth (river mile 0) showing river segments tracked by the Nebraska Game and Parks Commission (NGPC) and the US Geological Survey. Figure 1. The Missouri River from Gavins Point Dam to the confluence with the Mississippi River, showing all pallid sturgeon location points. The USGS stretch covered the remaining 367 river miles from Kansas City, MO to St. Louis, MO (Figure 2). Occasionally fish were found outside of the Missouri River, two fish were located in the Mississippi River and one in the Big Sioux River. The three fish that ranged beyond the Missouri River were included in the calculations for this study. Using SAS statistical software, we calculated 95% use distributions for individual fish in this study. Only fish with greater than three relocations were included. A 95% use distribution is the extent of area with a 95% probability of occurrence of a specific fish during a specific time period. Use distributions were used to help describe geographic space-use requirements of telemetered pallid sturgeon during 2008 and 2009. The data was log transformed to meet the assumption of normality, t-tests were used to identify statistical differences, and geometric means were reported. Results: A total of 98 pallid sturgeon were located from 2008 through 2009. At any given time, roughly 85 individuals were at large. Some individuals were lost due to tag failure and new fish were caught, implanted and introduced to the study through trotlining and gill netting efforts. Of these 98 sturgeon, 62 were male, 32 were female and four were of unknown sex. We could not detect a difference in use distribution size by sex in 2008 (t=0.70,p=0.49,df=71) or 2009 (t=1.97, p=0.053, df=57). Use distributions were significantly smaller in 2009 than 2008 (t=3.38, p=0.001, df=130). The geometric mean 95% use distribution for 2008 was 48.6 (n=73, SE=1.2) river miles and the geometric mean 95% use distribution in 2009 was 18.9 (n=59, SE=1.3) river miles. The ranges of individual 95% use distributions varied widely (Figure. 3 and Figure. 4). The graphs illustrate the differences between the two years and show the extent to which the use distributions of individuals can differ. No statistical tests were conducted to investigate a relationship between river mile and use distribution size, but use distributions appeared to grow larger as an individual’s farthest downstream location ranged farther from the dam. This study focused on the area of the Missouri River from Gavins Point Dam near Yankton, SD to the mouth of the river near St. Louis, MO. This stretch encompasses 811 river miles (~1,305 km) (Figure 1). The unchannelized segment extends from Gavins Point Dam (River Mile (RM) 811) to RM 753 (River Kilometer (RKM) 1212) near Ponca, NE. Morphology of the unchannelized reach remains largely unaltered with predominately sand substrates and a system of braided channels which create sand bars and islands throughout the reach. This section exhibits a wide range of depth and water velocities. At RM 753 (RKM 1212), the river enters a series of training structures that channelize the river by the time it flows through Sioux City, IA. The Missouri River remains channelized for roughly 733 river miles (1180 river km) before reaching the Mississippi River. In the channelized section of the Missouri River the channel has been restricted by revetted outside bends and dike structures on inside bends to manipulate the river for navigation and flood control. Habitat in the channelized section is very homogeneous and is characterized predominately by sand and silt substrate. Discussion: Pallid sturgeon with large use distributions likely undertook spring spawning migrations. Evidence suggests that sturgeon in the upper reach of the lower Missouri River may be experiencing interruptions in spawning activity due to the lack of a natural hydrograph. Gavins Point Dam itself also presents a physical barrier to fish migration. Our analyses show that pallid sturgeon use distributions are highly variable and may be dependent upon an individual’s reproductive status. As a result of alterations such as dams, reproductive fish may have their use distributions altered in ways that prevent them from successfully spawning. Altered migration routes may contribute to reduced reproduction and recruitment of the pallid sturgeon. By comparison, the fish in the lower reach act in a way that is similar to other sturgeon species when spawning. Their spawning behavior is also much more consistent from year to year. We believe that this can be attributed to the more natural hydrographical conditions in which they live. Unlike the NGPC stretch, the flow regime of the USGS section of the river is not dominated by water releases from Gavins Point Dam. The primary factor determining flow in the USGS stretch is water coming from tributaries. In a given year, pallid sturgeon utilize extensive stretches of the Missouri River and altering any part of the river system may potentially impact a large portion of the population. These analyses highlight the mobility of this species and the necessity to manage the pallid sturgeon at a range-wide scale. In the NGPC section of river, a core stretch was tracked 1-2 times per week from February to December of each year. The core stretch included the area of the river where the majority of the sturgeon resided most of the time. The core section, tracked by NGPC was 156 miles long (251 km). It began at RM 691 (RKM 1112), near Decatur, NE and continued downstream to Brownville, NE at RM 535 (RKM 861). The USGS reach did not have a similar core stretch because the fish in the that reach were more dispersed. Crews from the USGS also attempted to locate the fish in the lower section1-2 times per week. Figure 3. The 95% use distribution location and range for 77 adult pallid sturgeon with greater than 3 relocations in 2008. The total of 77 includes 4 individuals of unknown sex. They are not included in the statistical analysis. Each vertical line represents the range in river miles in which a specific individual could be found 95% of the time during 2008. The data are ordered by the lower bound of the 95% use distribution. Figure 4. The 95% use distribution location and range for 59 adult pallid sturgeon with greater than 3 relocations in 2009. Each vertical line represents the range in river miles in which a specific individual could be found 95% of the time during 2009. The data are ordered by the lower bound of the 95% use distribution. YearSexn Geometric Mean UD (River Miles)SE 2008 a 7348.61.2 Males a 48 53.11.3 Females a 25 40.91.3 2009 b 5918.9 1.3 Males a 4224.81.3 Females a 179.71.5 Table 1. Number of observations (n), mean, and standard error of use distributions for telemetered pallid sturgeon in the Middle Missouri River in 2008 and 2009. Superscript denote significance at an α=0.05 level for t-tests of difference between years and difference by sex within each year. In an attempt to ensure that all fish were relocated, tracking crews conducted monthly river sweeps. These sweeps encompassed the entire 811 river miles, when water levels permitted. The NGPC stretch was 444 river miles from Gavins Point Dam to the confluence with the Kansas River (RM 367), near Kansas City, MO.