Pallid sturgeon exist almost exclusively in habitats that are notoriously difficult to study. Particularly due to river flow and turbidity, there are many aspects of sturgeon behavior which scientists struggle to observe and truly understand. One such behavior which Comprehensive Sturgeon Research Project (CSRP) scientists are currently working to understand better is the tendencies, habits, and mechanics of egg deposition and fertilization. Despite being able to track pallid sturgeon and occasionally identify spawning locations, spawning behaviors in the wild have yet to be thoroughly documented.
Figure 1. The substrate and configuration of the CERC’s sturgeon study pond are shown. The “T” configuration of the gravel simulates gravel substrate lying parallel and perpendicular to the bank. The center wall facilitates current and the “H” frame shown is mounted with a DIDSON imaging sonar to observe fish behaviors.
Scientists reproduced sturgeon spawning habitat in a controlled environment at the Columbia Environmental Research Center (see Figure 1) in an attempt to study spawning and egg deposition up close. Water circulators set up within a 90×65 feet pond simulated the river current while gravel bars arranged both parallel and perpendicular to the pond banks simulated the two reproductive substrate arrangements believed to be utilized in the wild. An acoustic Doppler current profiler (ADCP) (see Figure 2) created a three dimensional profile of the pond’s currents (see Figure 3) prior to fish introduction and a DIDSON imaging sonar was employed to visually monitor the behavior of the fish over the course of the study. Before being released into the pond, reproductively-ready sturgeon were injected with hormones to induce ovulation in females or sperm production in the males. If all goes as it should females induced with hormones should ovulate and deposit their eggs within 12 to 24 hours of the final injection and release into the pond.
Figure 2. A River Ray aDcp deployed on a catamaran is shown mapping the CERC sturgeon study pond’s water currents prior to the introduction of sturgeon.
Figure 3. A cross section of the CERC sturgeon study pond’s water velocities is shown as mapped by an aDcp. The darker colors on the left side of the scale represent slower current velocities while the lighter colors on the right side of the scale represent faster current velocities.
The initial trial was conducted with shovelnose sturgeon. Subsequent trials will be conducted with pallid sturgeon. The reproductive physiology of both species is very similar, and the mechanisms of ovulation and egg deposition are likely similar as well. While shovelnose sturgeon may not have the same spawning behaviors or prefer the same spawning habitat as pallid sturgeon, the two species are known to hybridize where habitat has been highly modified. It is believed a better understanding of spawning behaviors will translate to a better understanding of habitat requirements for spawning adults and factors that may reduce the threat of hybridization.
Completed with contributions from Aaron DeLonay and Robert Jacobson
Each spring biologists and volunteers from State and Federal agencies cooperate to collect adult pallid sturgeon from the Lower Missouri River for hatchery propagation. Offices from the U.S. Fish and Wildlife Service, Missouri Department of Conservation, Nebraska Game and Parks Commission, and the South Dakota Game Fish and Parks send boats out to collect pallid sturgeon using trotlines and gillnets. The numbers of adults collected each year varies with the weather, river conditions, and luck. Captured pallid sturgeon are transported by special tank trucks to one of the participating fish hatcheries, including the Missouri Department of Conservation’s Blind Pony Fish Hatchery, and the U.S. Fish and Wildlife Service’s Gavins Point or Neosho National Fish Hatcheries. As the biologists on the river doing the collection are unable to discern reproductive fish from non-reproductive fish, all pallid sturgeon greater than 850 mm (33.5 inches) are taken to a fish hatchery to have their reproductive readiness assessed by USGS biologists using ultrasound and endoscopy. Fish that not reproductively ready are released back into the river as soon as possible, while those that are ready to spawn are held until conditions are right.
Missouri Department of Conservation hatchery personnel look on as Aaron DeLonay, USGS sturgeon biologist, surgically implants a pallid sturgeon with a telemetry tag.
When fish are no longer of use to the hatcheries, they are often taken by USGS scientists and implanted with transmitters and data storage tags immediately before release. This is an efficient way to increase the number of tracked sturgeon with known reproductive status and histories. Greater numbers of sturgeon tracked provide a better opportunity to learn how well sturgeon are growing in the river and how often sturgeon reproduce. Between April 30th and May 2nd, 21 pallid sturgeon captured during broodstock collection efforts were turned over to USGS biologists for surgical implantation of transmitters and data storage tags. Four other fish already had transmitters when they were captured for in the broodstock effort. These sturgeon were reimplanted with new tags. All fish were transported back to the river and released where they were initially caught. In the past year, 59 pallid sturgeon were tracked downstream of Gavins Point Dam in the Missouri and Platte rivers. We hope that with increased numbers of fish being tracked, patterns of habitat use and reproductive behavior may become more apparent.
With contributions from Aaron DeLonay and Robert Jacobson
On May 7th, the CSRP sampling crew on the Missouri River in Nebraska reported the first free embryo capture of the season. Crews equipped with fine mesh nets have been sampling the Missouri and Platte Rivers for drifting embryos since April 15th in an effort to identify when and where sturgeon and paddlefish spawning naturally occurs (see, We’ve Only Just Begun). Newly hatched sturgeon and paddlefish embryos are nearly indistinguishable, and it is unknown yet which species has been captured. That distinction will be made using a microscope in the laboratory when the samples are returned to the Columbia Environmental Research Center at the end of the week. Temperatures at the sampling location (14.5 degrees Celsius) were below temperatures where most sturgeon spawning occurs (16-22 degrees Celsius). Based upon experience from previous years, it is likely that the free embryo captured is a paddlefish. Paddlefish often spawn earlier and at cooler temperatures than shovelnose sturgeon or pallid sturgeon. With no previous captures in the first three weeks of the sampling season, this signifies the first tangible confirmation that the spawning season in the Lower Missouri River above the Platte River is underway.
With contributions from Aaron DeLonay
Figure 1. A paddlefish or sturgeon embryo captured May 7th during larval sampling of the Lower Missouri River.
By Casey Hickcox and Aaron DeLonay
Each spring CSRP biologists evaluate their list of tagged fish and search the river for pallid sturgeon that are expected to spawn. Because sturgeon do not reproduce every year there can be considerable variation in the numbers of tagged fish that are expected to spawn each year. This year there are very few fish with telemetry tags downstream of Kansas City. Currently, biologists believe there may be only one tagged reproductive female pallid sturgeon in the lower study section from the Kansas River confluence downstream to the mouth of the Missouri River. This fish, pallid sturgeon PLS11-005, was last located on March 26 near river mile 244 and has since gone undetected. With spawning season quickly approaching, the question of where PLS11-005 is and whether or not she is going to spawn this season was becoming critical.
In an effort to locate PLS11-005, two USGS tracking boats searched approximately 75 miles on April 21st between Kansas City and Waverly, Missouri (Figure 1). The area being searched had been identified based on the fish’s last known location. Previous searches above and below the target area came up empty. When an important tagged fish, like PLS11-005 goes missing it can be difficult to relocate. Pallid sturgeon are mobile and can migrate more than twelve miles a day in the Lower Missouri River. Tracking crews must search quickly, but carefully. On any given day a missing sturgeon, like PLS11-005 could be located behind a river-training structure or sandbar capable of masking her telemetry signal, or she could have moved into a previously searched area and could go undetected that day. These are just some of the many challenges facing scientists trying to track and understand these rare and elusive fish using acoustic telemetry (see previous post, “Can You Hear Me Now.”)
Figure 1. Map of telemetry locations for female pallid sturgeon PLS11-005 and search efforts during April 2014.
On this day, she would indeed go undetected. After 6 hours of searching with two different boats, only one tagged fish (a male located near river mile 344) was located. An attempt by another boat on the following day also failed to locate PLS11-005 downstream of Waverly. While biologists work to locate her, boats continue to track other tagged pallid sturgeon, including three reproductive females in the upper study section downstream of Gavins Point Dam.
After a long, cold winter, the Redbud and Dogwood trees are blooming and water temperatures are rising (Figure 1). Spring seems to have finally sprung, and fish, and hopefully the endangered pallid sturgeon among them, will soon be spawning. In an effort to better understand pallid sturgeon spawning, fertilization, hatch, and dispersal, Comprehensive Sturgeon Research Project (CSRP) biologists initiated weekly sampling efforts for Acipenseriformes (sturgeon and paddlefish) free embryos on April 15. The work is occurring at two sites in Nebraska; one upstream of the confluence of the Missouri and Platte rivers (near river mile 600) and the other is located less than one mile up the Platte River.
Figure 1. Temperature and discharge of the Missouri River at U.S. Geological Survey streamgage 06601200 Decatur, Nebraska.
In order to sample the swift waters for Acipenseriformes free embryos, CSRP researchers deploy a pair of very fine, cone shaped ichthyoplankton sampling nets attached to 100 pound lead weights into the water column using winches mounted to each side of an anchored boat. The nets filter water through a 0.5 meter opening and the drifting embryos are captured by the nets. The nets must be made with a very fine mesh (0.75 mm) to prevent the small tadpole-like larvae (7-8 mm) from slipping through.
The sampling nets are simultaneously brought back up (Figure 2) to the surface after a set period of time (5 to 15 minutes, depending on the debris load suspended in the water column). The contents of the sapling nets are emptied into pans, where Acipenseriformes free embyros are hand-picked from the debris. Recently hatched sturgeon and paddlefish free embryos are too small and similar to differentiate, so they are preserved in alcohol and returned to the laboratory where they will be identified to genus using a microscope. Sturgeon specimens will be sent to a genetics laboratory to determine if they are shovelnose sturgeon, or if we are very lucky, the endangered pallid sturgeon. We haven’t caught any Acipenseriformes free embryos to date (April 30), but spawning season is just beginning.
Figure 2. Biologists sample the water column of the Missouri and Platte Rivers to collect sturgeon or paddlefish free embryos).
With contributions by Aaron DeLonay
In the late fall or at the end of winter of previous seasons, Comprehensive Sturgeon Research Project (CSRP) biologists would send boats out into the field to seek out a few, rare pallid sturgeon females to implant with transmitters in hopes of tracking them to their spawning locations. This has been our dominant approach to characterizing where and when spawning is occurring. Beginning in 2014 the project focus has shifted slightly towards longer-term science objectives. In addition to tracking reproductive females, biologists are also emphasizing recapturing and retagging as many telemetered pallid sturgeon as possible to reimplant them with tags and fresh batteries in hopes of maintaining a population of tagged pallid sturgeon that can be monitored through several reproductive cycles. Biologists also hope to increase the number of tagged males in the study population to help identify possible aggregation areas and to answer the long-standing question of which sex ultimately chooses where spawning occurs.
Since recapture efforts began in the fall of 2013, CSRP crews have recaptured more than 15 telemetered pallid sturgeon and identified three females (PLS11-019, PLS10-029, and PLS12-002) and one male (PLS10-032) pallid sturgeon nearing spawning condition. Each of these fish has a long history with the CSRP and researchers will be particularly interested in their movements and behavior. At the end of April, more than two dozen additional pallid sturgeon collected during the annual pallid sturgeon broodstock collection efforts will be implanted with transmitters and added to the study population. During 2014, telemetry studies of habitat use and spawning will be augmented by laboratory studies of spawning, egg hatch, and free embryo dispersal to examine further the factors that may be limiting survival and recruitment of young sturgeon in the river.
With contribution from Aaron DeLonay
CSRP Biologist Sabrina Davenport prepares to release a reproductive feamle pallid sturgeon.
During the past few months, Comprehensive Sturgeon Research Project (CSRP) biologists in Columbia have been planning and preparing for a controlled experiment to develop a better understanding of the behavior of pallid sturgeon embryos at the critical moment they emerge from the egg. Pallid sturgeon eggs are adhesive and spend the first few days as developing embryos in the substrate near where they are spawned. Once the embryos hatch they can either burrow into the substrate to continue their development in place, or swim up into the water column and be immediately swept away with the current. The ability of pallid sturgeon free embryos to remain in or utilize available substrate to continue their development after hatching, even for a short period, would reduce the downstream dispersal distance that pallid sturgeon free embryos need before they transform into feeding larvae and settle to the bottom to begin feeding. Researchers will use experimental streams with sand, gravel or cobble bottoms to help to determine the influence of these substrates on hatch and initiation of dispersal of pallid sturgeon free-embryos (see previous post “A Rocky Start”).
In order to obtain pallid sturgeon embryos, which will be seeded into the controlled stream experiments, CSRP biologists conducted an inventory of the captive population held at the research center in search of reproductive individuals. Each pallid sturgeon was weighed, measured, and a reproductive evaluation was performed using non-invasive ultrasound techniques to determine if the fish would be ready to spawn this spring (see previous posts, “Catch Me If You Can,” and “Did She or Didn’t She” for descriptions of ultrasound). If a female was found to have late-stage, maturing oocytes (eggs), a biopsy was performed to remove a few of the eggs to determine how close she was to spawning. Males also were examined with ultrasound for changes in density of testes and the development lobes that signify that they too will be ready to spawn in spring. Individuals expected to be reproductive this spring were moved to a separate research pond where they will be monitored as temperatures rise and spawning season approaches.
CSRP biologists conducted an inventory of the captive pallid sturgeon population held at the Columbia Environmental Research Center. Each pallid sturgeon was weighed, measured, and a reproductive evaluation was performed using non-invasive ultrasound techniques to determine if the fish would be ready to spawn this spring.
CSRP biologists have been planning and preparing for a controlled experiment to develop a better understanding of the behavior of pallid sturgeon embryos at the critical moment they emerge from the egg. Researchers will use experimental streams with sand, gravel or cobble bottoms to help to determine the influence of these substrates on hatch and initiation of dispersal of pallid sturgeon free-embryos (cobble substrate pictured above). The embryos will be obtained from the captive pallid sturgeon population at the Columbia Environmental Research Center.
As spring progresses, the fish will be moved to holding tanks inside the lab where their eggs and milt will be collected and combined under controlled conditions. The fertilized eggs will be placed into the experimental streams where they will develop and hatch. Hatched embryos will be monitored to determine if different sized substrates influence the tendency of free embryos to stay in the substrate or initiate downstream dispersal in the current. Although full expression of environmental conditions in the Missouri River cannot be replicated in our experiments, we can add useful understanding about early innate behaviors of pallid sturgeon that may influence management strategies for recovery.
Completed with contributions from Sabrina Davenport and Aaron DeLonay
Story by Robert Jacobson
I finally had a chance to visit the Deer Island restoration site the week of April 1 (fig. 1). Deer Island is a 2.5-mile long reach of the Missouri River near Little Sioux, Iowa where the US Army Corps of Engineers has nearly doubled the channel width while increasing habitat diversity. Unlike all other shallow-water habitat (SWH) projects on the Lower Missouri River, the Deer Island project was designed to build habitat completely to the final condition. Other projects have relied on a pilot channel or an initial widening effort that is expected to grow over time as the river takes advantage of the opportunity to erode and deposit sediment, adding habitat diversity by creating shallow, slow water. The pilot approach minimizes construction costs – because the river does the work – but adds uncertainty about what the final state of the channel will look like and, critically, when it will be achieved. The uncertainty about whether SWH restoration sites are still evolving means that evaluations of the SWH program have been aiming at a moving target.
Figure 1. One of multiple rock and log structures at Deer Island restoration site. Photo is looking from east to west, across restoration area toward navigation channel.
The Deer Island site is fundamental to quantifying restoration on the Missouri River because it does not use a pilot approach and because it is located perfectly for a before/after comparison (fig. 2). An earlier USGS study on effects of the “spring rise” on pallid sturgeon habitat selected the exact same reach in 2006 because it was representative of the channelized Lower Missouri River between Sioux City, Iowa and Rulo, Nebraska. This study (Jacobson and others, 2009) developed detailed information about channel conditions, habitat availability, and background rates of channel change – a perfect pre-project comparison to quantify added habitat value. Ongoing biological and physical monitoring of the Deer Island site by the Missouri River Recovery Program – Habitat Assessment and Monitoring Project (HAMP) promises to help quantify the linkages between new habitat and biotic responses.
Figure 2. Map of the Deer Island restoration site showing approximate limits of channel widening project and the area previously mapped and modeled by USGS.
Icy blasts of arctic air brought bitterly cold temperatures to the Missouri River Basin late in December 2013 and early January 2014. The frigid temperatures created significant ice flows in portions of the Lower Missouri River, hampering pallid sturgeon tracking efforts. In addition, low water levels have restricted access to the river at several locations between Kansas City and St. Louis. This is not the first time that winter-related weather has delayed tracking activities (see previous posts “How Low Can It Go?” and “Ice Ice Baby”). The river does not freeze solid in Missouri, instead “pads” of ice usually form and slowly fill the river, crushing and grinding together as they make their way downstream. When the ice fills the river you can stand on the river bank and listen as it moves slowly past—if you are willing to brave the cold. CSRP biologists prepare for winter tracking efforts by routinely checking ramp and river conditions and conducting maintenance on tracking vessels and equipment. Taking these extra steps ensure that our crews are ready to get back on the water safely, conditions permitting.
Blasts of arctic air brought freezing temperatures throughout the Missouri River Basin near the end of December 2013 (source of graphic: National Oceanic and Atmospheric Administration).
Frigid temperatures created significant ice flows throughout the Lower Missouri River, hampering pallid sturgeon tracking efforts. Pictured is the Lower Missouri River at Hartsburg, MO near river mile 160.
It may seem a bit early to ask this question, but the spring spawning season is never far from CSRP biologist’s minds (see previous post Thinking Ahead). Preparations for the 2014 spring season started early in the fall when crews began locating tagged female pallid sturgeon that they believed would become reproductive in the spring. Once a targeted female had been located, biologists drifted trammel nets over her location until the fish became entangled in the net and could be pulled into the fishing boat. The fish was then placed into an aerated holding tank where biologists used non-invasive ultrasound techniques to check for the presence of developing immature eggs (oocytes). Any females determined to have oocytes will be intensively monitored in the spring of 2014 in the hopes of determining her spawning location.
During the week of September 16th, CSRP biologists recaptured and evaluated three female pallid sturgeon (PLS11-019, PLS10-029, and PLS12-002) expected to be in reproductive condition this coming spring. PLS11-019 was first implanted with a telemetry transmitter in 2011 and released near river mile 717.1 near Sloan, IA. PLS11-019 is expected to spawn for the second time in 2014 and will be tracked by biologists in the CSRP project. She was first documented to have spawned in the Missouri River during the spring of 2012 between river miles 700 and 714. Determining how often pallid sturgeon females spawn, and if they return to the same places to spawn time after time, is critical information for biologists.
PLS10-029 was first telemetry tagged in the spring of 2010 near river mile 563.7. She was last in reproductive condition in the spring of 2012 and is also ready to spawn again after only 2 years. Tracking efforts and retrieved data storage tag (DST) data have shown her to make spring migrations up the Platte River in both 2011 and 2012 (See previous post “Where Are You When I’m Not Looking?”). It is likely that PLS10-029 spawned in the Platte River in 2012. Since then she has spent most of the last two years between Plattsmouth and Bellevue, NE. Biologists expect that she will again migrate up the Platte River in the spring of 2014.
PLS12-002 was first telemetry tagged in the fall of 2012 near river mile 576.2. Based on the presence of a coded wire tag, biologists were able to determine that PLS12-002 was originally produced in a hatchery. PLS12-002 was last located at river mile 513 during October 2013’s river sweep. PLS12-002 is evidence that hatchery-produced pallid sturgeon can grow and reach reproductive condition in the contemporary Missouri River. Whether hatchery progeny will spawn with other pallid sturgeon at the same spawning locations, and successfully contribute to the recovery of the species has not yet been established. Biologists are hopeful that fish such as PLS12-002 will provide that needed insight. All three females will again be targeted for recapture in the spring of 2014 for evaluations of reproductive readiness.
Initial recapture and current telemetry locations for three reproductive female pallid sturgeon (PLS11-019, PLS10-029, and PLS12-002) expected to spawn in the spring of 2014.