Saving the Pallid Sturgeon
If time travel existed, you could go back 100 million years and find the same fish we see today gliding across the floors of the Missouri and Mississippi rivers. Seeing a pallid sturgeon is like glimpsing the past — this ancient species has existed since the days of the dinosaurs. The pallid sturgeon is one of the largest freshwater fish in North America, growing between two and six feet long (or, roughly four bananas up to the width of a king-size mattress) and up to 85 pounds — so, about the size of a 12-year-old child.
The Dinosaur of the Missouri River
Living at the depths of mighty rivers, the pallid sturgeon has always been a rare sight. In the 1960s, the pallid sturgeon became even more rare when the population started to decline dramatically. By 1990, the numbers had dropped significantly enough that the species was listed as federally endangered. Recovery efforts were underway shortly thereafter, and the U.S. Fish and Wildlife Service and its partners are working hard to recover this ancient species to this day — keep reading to learn more about this fish, why its population declined, and the efforts to restore this special species.
The Missouri River (the longest river in North America) serves as the main artery for the Midwest, supplying water to half a million square miles, stretching from Alberta to Missouri. This river system plays a critical role in the long-term survival of the pallid sturgeon. Although dams and dikes changed the river, portions of the Missouri River still remain somewhat wild and support ecosystems for about 300 species of birds and 150 species of fish — including the pallid sturgeon.
The dams and dikes along the river have changed the way the water flows downstream. Large river habitat alterations, including river channelization, bank stabilization, impoundment, and altered flow regimes, have been linked to the modification and curtailment of the Pallid sturgeon’s habitat and range. These changes greatly reduced the river’s ability to satisfy the needs of Pallid sturgeon by: blocking movements to spawning and feeding areas, trapping sediment in reservoirs, altering water temperatures and flows, and possibly reducing food sources. The pallid sturgeon is a naturally slow-growing, slow-maturing fish, which makes the species particularly vulnerable to sharp population declines.
Scientists are also evaluating the impact of contaminants on Pallid Sturgeon. Because pallid sturgeon are at the top of the food chain and have a long lifespan, they may be at elevated risk to contaminants that bioaccumulate and cause reproductive impairment. Since 2008, studies have identified pesticides, metals, hormonally active agents, and nutrients as contaminants of concern throughout the species’ range. Other factors that potentially played a role in the decline of the Pallid sturgeon include disease, overutilization for commercial, recreational, scientific, or educational purposes, energy development, hybridization, and invasive/nuisance species.
Recovering a Relic
Efforts to recover the pallid sturgeon began in earnest in the nineties after the species was listed as endangered in 1990. The U.S. Fish and Wildlife Service began working with state and federal partners to learn about the pallid sturgeon’s ecological needs and to determine options for its recovery — including artificial reproduction, habitat improvements, and reducing mortality from commercial fishing (before being listed as endangered, pallid sturgeon were considered to be fine eating, as well as trophy sport fish, and their roe was used for caviar). One of the most exciting undertakings was the establishment of a captive breeding program, led by the U.S. Fish and Wildlife Service’s Fisheries Program. Wild reproduction of pallid sturgeon is actually extremely rare, and in some cases, nonexistent. Scientists had to act fast to stabilize the species before it went extinct.
One of the most fascinating aspects of the pallid sturgeon is its expected life span — which is anywhere between 50 to 100 years. But this does come with a drawback: because their lifespan is long, it takes several years for pallid sturgeon to reach reproductive maturity (up to 15–20 years for females, 9–15 for males), and many years can pass before the fish are capable of spawning again. This makes spawning efforts challenging, even in captivity. After years of captive spawning trials, in 1997, through a combined effort between multiple U.S. Fish and Wildlife Service programs, North Dakota Game and Fish, and Montana Fish, Wildlife & Parks, scientists successfully spawned two female and three male pallid sturgeon
These pioneering efforts laid the groundwork for what is, today, a large, inter-agency effort across seven states — North Dakota, South Dakota, Missouri, Montana, Nebraska, Kansas, and Iowa. The pallid sturgeon breeding program includes annual spawning of wild-captured (and later released) adults, as well as maintaining a captive broodstock (fish spawned in captivity and kept year-round). The captive broodstock serves to genetically represent the wild population, while providing a safety net in the event of catastrophic loss in the wild.
When an adult pallid sturgeon is captured and deemed ready to spawn that season, it is taken to a National Fish Hatchery (NFH) — usually Garrison Dam in North Dakota, Gavins Point in South Dakota, or Neosho in Missouri — where it is closely monitored. It is important to reduce stress, handling, and exposure to protect the health of the fish and prevent disease outbreaks. To this end, fish are transported as little as possible and sent to the closest available facility — this also helps keep genetic information local, which is used to produce the next generations for the local population.
This June, the team at Garrison Dam NFH was able to spawn three females and five males — resulting in 635,000 eggs. The scientists are using the embryos in a study to better understand how larval fish react and survive in the wild during the first week after hatching. They also collect data about water flow and temperature conditions to make informed decisions regarding dam management operations.
At Garrison Dam and the Bozeman Fish Technology Center, scientists are using larval fish from the captive broodstock in a feed study. The goal is to discover and better understand the dietary needs and food preferences of larval pallid sturgeon as they adjust to the outside world. Feed studies are critical to the survival of larval pallid sturgeon, which experience high levels of mortality during this infancy phase. Gavins Point NFH also had a successful spawning season this year, spawning 81 pallid sturgeon (42 males and 39 females) this spring, resulting in a stunning 1.26 million eggs. Of the 81 sturgeon, 10 were wild fish that were later released back to their original habitats.
Next spring (2020), the pallid sturgeon fingerlings (little baby sturgeons) hatched from the 2019 spawning efforts will be released into the Lower Missouri River along a 800-mile stretch from south-east South Dakota to St. Louis, where the Missouri meets the Mississippi. This cycle will continue each year until pallid sturgeon can sustainably reproduce on their own in the wild.
In addition to captive breeding and wild reproduction, researchers with the U.S. Fish and Wildlife Service, U.S. Army Corps of Engineers, and state agencies are augmenting these efforts with habitat restoration activities. Each year, these agencies come together to evaluate planned construction and maintenance projects, and identify habitat restoration and improvement opportunities. Scientists monitor these efforts and collect data to reveal population trends in response to habitat restoration activities, then use that data to guide future restoration projects. Some of the information scientists are looking for include the effectiveness of dikes to restore riverine functions, the impact of leaving cleared woody debris in the ecosystem, and the impact of dam operations on downstream larval fish.
A Long River Home
The final step in the captive breeding program is to collect data from the fish once they have been in the wild for a few years. This data gives researchers critical information about pallid sturgeon survival rates and population estimates in the wild. Although still not abundant, captive-bred pallid sturgeon have been found to be surviving and maturing in the wild: in recent years, researchers have been able to track down adult pallid sturgeon that were part of spawnings in the late 90s and early 2000s. This is exciting progress, providing early hope in the successful recovery of the pallid sturgeon. But this is not the end of the story.
It may take another 20 years to see if the offspring of captive-bred fish can spawn in the wild, which is a critical milestone for pallid sturgeon to be able to, once again, achieve self-sustainable population growth for future generations. The U.S. Fish and Wildlife Service and its state and federal partners are committed to seeing the pallid sturgeon reach this milestone, no matter how long it takes.