Sturgeon are incredibly resilient fish. Fossil records of sturgeon date back to the Cretaceous period—more than 260 million years ago. Today, there are 25 different species of sturgeon worldwide. But due to overfishing, water pollution, vessel strikes, and lack of access to habitat they need, many sturgeon species have declined. Nine species of sturgeon are listed as either threatened or endangered under the Endangered Species Act. They are considered one of the world’s most endangered groups of species.
There are five distinct population segments of Atlantic sturgeon in the United States. Four of these segments are considered endangered. The other is considered threatened.
One of the distinct population segments of this fish that is endangered is located in the Chesapeake Bay. To help the Chesapeake population rebound, NOAA is working with partners to:
- Study their abundance, reproduction, and distribution
- Identify and protect habitat they need during their life cycle
- Minimize dangers they face, including from ship strikes
- Introduce students to these fascinating fish
Telemetry Helps Track Fish Numbers, Movement
One way scientists learn more about Atlantic sturgeon is by tracking their movements using acoustic telemetry. Telemetry uses sound to relay information across open space. Scientists surgically insert special sound-emitting tags into fish. Then, receivers stationed in the water detect when those tagged fish swim near the receivers. Understanding sturgeon movement over time and space can help efforts to protect them.
“We tag sturgeon every year, and we’re trying to maintain about 100 active tags,” said Dr. Jason Kahn, NOAA Fisheries’ Office of Protected Resources, of an effort based in Virginia’s York River. “Generally that means tagging about 10 to 15 fish per year.”
The largest telemetry tags have batteries that last for about 10 years, but smaller tags may only last for a few months.
“There are two tags from 2013 that are still working. But we have retagged perhaps 10 or 12 fish when they got toward the end of one tag’s battery life, so that really extends the time we have information on individual fish,” Kahn noted.
Telemetry data can help scientists estimate sturgeon survival rates, spawning frequencies, migration timing, migration corridors, and much more. It can also tell us what types of habitat sturgeon use.
When researchers capture sturgeon to tag them, they get other information such as population estimates, fish size, sex, and health. When previously tagged fish are recaptured, scientists get an additional information boost.
“The modeling I have done in the York River basically puts us between 97 and 99 percent survival per year for the adults, which is great. But sturgeon naturally reproduce roughly 20 times or more in their lives, so any human-caused mortality reduces their potential to produce offspring,” Kahn said. “We have some indication that things are getting better in the York River. We’re capturing fish we also captured in previous years that are growing bigger, but also seeing a lot of new adults that are small, suggesting they’re recently maturing. Without modifying our sampling strategy, we’re seeing more females in the last couple of years, so that makes us hopeful.”
Finding Fish Where There Were Thought to Be None
While researchers have focused on Atlantic sturgeon for many years, new studies are revealing things about them we never knew. Dr. Matt Balazik is a scientist with Virginia Commonwealth University. Scientists once thought that there were no more sturgeon in the James River, but that is not the case. Dr. Balazik has been studying them for about 20 years.
“In the James River, we have been seeing a pretty healthy adult population, but low spawning success,” he says. “We may have had some initial success after the Clean Water Act was passed, helping the population to recover a bit. But now we’re trying to determine why the juvenile numbers aren’t growing, which would then eventually help grow the adult population.”
While the number of adult sturgeon in the James River—and the Chesapeake Bay in general—seems to be holding steady, the lack of juveniles is a bit of a mystery. Scientists are exploring whether this may be due to predation, lack of suitable habitat, poor water quality, or other reasons.
Dr. David Secor, of the University of Maryland Center for Environmental Science, highlights some of the information studies in the James River have revealed: “We’ve learned some amazing things about these fish. We had completely missed them because they were doing things differently than we expected. We learned that they were spawning mostly there in the fall, when the historical information was that they were spawning in the spring. And then they were going so far up these tributaries. They are big fish, and we just couldn’t imagine them swimming up into these skinny channels. Telemetry was a principal way we discovered this.”
Identifying Sturgeon Habitat
Atlantic sturgeon seek out different kinds of habitat during their lives. They prefer to spawn in areas with a variety of hard bottoms. These areas can change from year to year, as high water flows can expose—or cover up—potential spawning grounds. So habitat scientists, including experts from the NOAA Chesapeake Bay Office, use sonar to analyze and identify areas that could be important spawning habitat for sturgeon. This information can help resource managers identify and protect potential spawning grounds.
“In the Marshyhope River [on the Eastern Shore of the Chesapeake Bay], the majority of the fish have been tagged. That’s possible because the population is smaller. We have tagged about 40 fish over the last 10 years. NOAA Fisheries' habitat work has been terrifically helpful for us as it helps us target areas where we might find juveniles to help us learn more about them,” said Secor.
Vessel Strikes: a Big Stressor
The Chesapeake Bay and its rivers see a lot of shipping traffic, including very large ships that reach almost to the bottom of the waters they transit. As Kahn explains, even if a sturgeon isn’t directly in the path of a ship, they can still face danger.
“When a propeller is moving to pull a boat of that size, it is really moving a lot of water. Ships coming into the James River are right at the bottom; often there’s only like a meter difference between the bottom of the boat and the river bottom. The water they are pulling has to come from somewhere, and it’s coming from the sides of the shipping channel. Even if fish aren’t right in the shipping channel, they’re still getting pulled through the propeller,” Kahn described. “They can swim away, but sturgeon are pretty lazy animals; they’re just trying to go with the flow. They have survived through millions of years of evolution without significant vessel threats until just recently.”
Unfortunately, it’s the larger fish that are more likely to be affected by ship strikes. While smaller fish may make it in between the blades of a propeller, the larger 6- or 7-foot-long fish are more likely to suffer.
“What we see is the fish we’re picking up that have been hit are disproportionately adult females, and from a recovery standpoint, that’s just a catastrophe. If we want to focus on recovery, reducing vessel strikes is the first thing we need to focus on,” said Kahn.
New technology may provide some help.
“There are real-time telemetry receivers now, which can provide management tools. Knowing that there are sturgeon around can let us know when ship strikes are more likely to happen,” said Secor. In the future, using that information could help resource managers and shipping experts team up to reduce shipping traffic strikes when more sturgeon are present.
Impact of Blue Catfish
Atlantic sturgeon may also face challenges from another fish: Blue catfish, which are an invasive species in the Chesapeake Bay. They were introduced into some rivers in Virginia as a sportfish. In the early 2000s, they began expanding their range around the Bay. And they like to eat pretty much everything.
“All of those juvenile blue catfish that are starving—that are 4, 5, 6 inches long—they are going to be mowing down sturgeon eggs and larvae. And when they are reproducing in the fall, at least in the James, what else is there that’s small for those little catfish to eat?” wonders Balazik.
Researchers are concerned about more than just what blue catfish eat.
“Another concern is habitat displacement, where sturgeon would normally prefer to be, based on research in neighboring rivers, is occupied entirely by blue catfish. When I sampled the deep, sandy holes where we’d expect sturgeon to be, I only caught blue catfish. There was very good species diversity along the edges of those holes, but at the bottom was just blue catfish. So that may mean that sturgeon are more vulnerable to predation in those holes and therefore choosing not to occupy what would otherwise be preferred habitat,” said Kahn.
Human-Made Challenges Abound, Including Climate Change
While sturgeon are tough fish, especially once they are large adults, it takes many years for them to grow to adult size. The faster they grow and get to adulthood, the better for the overall population. But poor water quality can make them grow more slowly.
“We’re trying to work with the U.S. Environmental Protection Agency to set better water quality standards so that we get better growth out of the fish and get them toward recovery more quickly,” said Kahn.
Climate change poses another challenge. Water temperature patterns are changing. In fall, fish generally wait for water temperatures to drop to between 70 and 77°F to spawn. There also seems to be a correlation between the peak of spawning and when the length of daylight in a day (the “photoperiod”) drops to 12 hours in late September. But a temperature-time squeeze is happening. Summer water temperatures are trending higher, so the right temperature for spawning is coming later in the year.
There will likely soon come a time when the preferred photoperiod and the preferred spawning temperatures do not match up. When we first started sampling in 2013, we found ovulating females from late August until late September. But in the York River this year, optimal temperatures and photoperiod only lasted from September 16 to 22. That leaves a very small time window in which the fall-spawning fish can create the next generation of sturgeon.
However, there is some good news: People are looking at innovative, collaborative ways to solve some challenges. For example, power companies often draw in water from rivers to cool their machinery. But this process can also draw in and kill fish.
“We work with the power companies that have water intakes, and when the females are up in that area, they will quickly reduce their intakes to potentially reduce their chances of pulling in a fish. They are willing to do this to help the sturgeon,” said Balazik.
The Next Sturgeon Scientists
Helping people learn about sturgeon and understand the challenges the species faces is an important part of protecting these fish, and toward helping them recover. To boost this effort, the NOAA Chesapeake Bay-Watershed Education and Training program provided a grant to ShoreRivers. The funding helped ShoreRivers work with Dorchester and Talbot County Public Schools in Maryland to teach all third graders in those counties about sturgeon conservation.
ShoreRivers’ project delivered professional development to teachers. It helped the third graders investigate issues about sturgeon, learn through outdoor experiences, collect data, and take action about sturgeon. Students researched the importance of sturgeon and explored how human actions on land affect sturgeon habitat in their local rivers. Their environmental actions include planting garden beds to decrease runoff from their school grounds, developing brochures to inform other students, and creating a mural to serve as a learning tool. Their innovative efforts help spread the word about the species and what we can all do to help sturgeon recover.
Reasons for Optimism
Despite all the challenges they face, sturgeon are built to last—but they need support.
“The adults are built to be resilient. They are showing up in places we don’t expect them, and I think it’s important to see that we are urgently optimistic about their fate because we have to do things to keep them going,” said Secor. “If we can reduce blue catfish predation and increase water quality, then this is a fish that—if things go right in a given year and they produce a strong year class—could support a positive trend for a decade or longer.”
And Dr. Balazik highlights how many people have come to love and treasure the ancient-looking species: “The sturgeon has become almost a symbol of the James River. There are people who do sturgeon tours; there are local beers named after them.”
With continued science, collaboration with partners, and education for the next generation of Bay stewards, sturgeon just may survive for another 260 million years here in the Chesapeake Bay.
