NOAA Atlantic Sturgeon Research

Sturgeon are ancient fish. Fossil records of sturgeon date back more than 260 million years ago to the Cretaceous period. Today, there are 25 different species of sturgeon worldwide.

Many sturgeon species have declined due to overfishing, water pollution, vessel strikes, habitat loss, and other factors. 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.

NOAA is tasked with an array of research on Atlantic sturgeon in the Chesapeake Bay. Projects include identifying and protecting sturgeon spawning habitats, seeking to minimize vessel strikes, education, and others.

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

Researchers are learning more about Atlantic sturgeon 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.

The largest telemetry tags have batteries that last for about 10 years, while smaller tags may only last for a few months. 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.

While researchers have focused on Atlantic sturgeon for many years, new studies are revealing things about them. While the number of adult sturgeon in the Chesapeake Bay watershed 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.”

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.

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.

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.

Atlantic sturgeon may also be stressed by 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. Scientists theorize that blue catfish may be eating sturgeon eggs or fry.

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.

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.

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.

Recently, a temperature-time squeeze has been happening. Summer water temperatures are trending higher, so the right temperature for spawning is coming later in the year. That leaves a short window of time that is suitable for sturgeon to spawn.

source: NOAA Chesapeake Bay Office