It took more than two years — and endless hours of frustration — before biologists found their first sturgeon on Marshyhope Creek.

Week after week, they went to the river and placed 100-yard gill nets, only to pull them out empty. Then, last fall they finally caught eight adult fish.

Now, they can find them any time they want. They just have to turn on their computer.

“They can’t hide from us because we have tags in them,” said Chuck Stence, a fisheries biologist with the Maryland Department of Natural Resources, referring to tiny electronic transmitters scientists had implanted in each fish.

About every 90 seconds, the transmitters send out a high-frequency signal that identifies the fish and its location. If there is a receiver nearby — roughly within a half-mile — it picks up and logs the information until biologists retrieve it and load it into their computers. Now, biologists know when the sturgeon are around and where they are hanging out. “We basically have the whole river wired now for sound,” Stence said.

It’s not the only wired place in the Bay. As the fish migrated out the Marshyhope and down the Chesapeake last fall, Stence was able to trace their movements along the Bay’s deep channel until they exited at the south end of the Chesapeake Bay Bridge-Tunnel.

Throughout the Bay, and all along the East Coast, scientists are tagging thousands of fish while building a network of receivers that allows them to track their movements in a way unimaginable little more than a decade ago.

Scientists believe the information they are gathering will help them locate critical habitats, such as spawning grounds, while shedding new light on coastal migrations, where fish may be vulnerable to nets targeting other species. Such data could help protect rare or threatened species, such as sturgeon, while improving management for more common fish, such as striped bass.

For centuries, much of the lives of fish, especially those that migrate along the coast, was hidden under the waves. Most of what scientists knew about their movements came primarily from tagging and recapture programs, in which biologists placed external tags on fish and waited for the fish to be captured and the tags returned, usually by fishermen.

“Now, we are more or less letting the fish tell that story rather than the recapture of tagged fish in fisheries, which provide a biased account of where those fish go,” said Dave Secor, a fisheries scientist with the University of Maryland Center for Environmental Science.

Secor has been placing high-frequency acoustic transmitters in striped bass captured in the Patuxent and Potomac rivers and tracking their movements through the Bay and along the coast. Mature female striped bass were thought to spawn annually, but Secor has found that some take a couple of years off between spawning runs — information that could never be gained from traditional tag and recapture programs.

Further, programs that hinge on recaptures don’t work well for species that are rare, like sturgeon, and therefore unlikely to be caught again. “This lets us find needles in a haystack, where you have really big water like the Bay or tidal river, and relatively few needles,” said Greg Garman, director of the Center for Environmental Studies at Virginia Commonwealth University.

Biologists began using acoustic tags more than a decade ago. Initially, they had to chase the fish in boats until the scientists grew too exhausted to follow. But new transmitters with longer battery lives and longer ranges keep pinging out information about a fish for years. Scientists began placing receivers along the shoreline — even on buoys — which could pick up pings and store the data.

Instead of chasing fish on a boat, biologists could walk away for weeks, or months, then download data from the receivers and load it into a computer. They can plot the movements of dozens, even hundreds, of individual fish logged by the receiver.

Unexpected pings

Then, something else began to happen — individual scientists began getting pings from fish they didn’t tag; they began encountering each others’ fish as they swam by. Instead of just tracking fish in a local river, they could — by exchanging information — track longer migrations.

“If you put these receivers out, you have the potential to hear from thousands of tags, and that has actually been happening,” said Dewayne Fox, a fisheries scientist with Delaware State University, and one of the first to use the acoustic technology.

After chatting with others at a fisheries meeting a decade ago, Fox led the establishment of the Atlantic Cooperative Telemetry Network, a collection of scientists who exchange data from fish tagged along the East Coast.

Altogether, roughly 100 scientists in the network have tagged nearly 10,000 individual fish over the last decade. They represent about 75 species, from alewife and striped bass to bluefin tuna and sand tiger sharks. “If you can think of something that swims in the ocean, chances are someone has put a tag on it,” Fox said.

Fox, who has tagged dozens of sturgeon, has seen them migrate from the mouth of the St. Lawrence River in Canada to Cape Canaveral off the Florida coast through the network.

Local tracking has helped him discover new areas of importance to the fish. “Having some of these animals tagged has led to areas where we had absolutely no idea that there were sturgeon,” Fox said.

Sturgeon are the most commonly tagged fish, accounting for about 1,500 acoustic transmitters in the network. That largely reflects the sturgeon’s endangered status, which has led agencies, such as the National Oceanic and Atmospheric Administration and the U.S. Navy, to invest in tagging and establishing arrays of receivers to track them.

In the Chesapeake, the Navy’s investment has been pivotal. With numerous installations, the Navy became concerned about how its operations might impact sturgeon when the species was listed as endangered in 2012. “We found there was very little data available,” said Carter Watterson, a marine fisheries biologist with the Navy in Norfolk. So, it funded research including the tagging of sturgeon and the establishment of a system of 75 acoustic receivers in the lower Chesapeake and into the Atlantic off the Bay’s mouth.

“Researchers up and down the coast have been tagging Atlantic sturgeons since 2005 with acoustic transmitters, so there was already a large population carrying acoustic transmitters,” Watterson said. “As soon as we set the array up, we started getting detections of these fish moving in and out of the Bay.”

Compared with some places along the coast, the Bay’s fish tracking capacity is small, but the Navy investment has helped it catch up. State agencies and individual researchers have also helped, placing dozens of other receivers around the Bay, and the NOAA Chesapeake Bay Office has put receivers on several of the “smart buoys” in its Chesapeake Bay Interpretive Buoy system. Altogether, there are about 125 receivers around the Bay, and the number grows each year as new places like the Marshyhope get wired, providing ever-greater detail about the movements of tagged fish.

That’s opened the door for Bay scientists to work with additional species, from striped bass to blue catfish to cownose rays.

“Once you have an array of receivers established, it is not that big a deal to buy 40 transmitters and put those in some other species,” Garman said. “Although this array was built for sturgeon, the sky is the limit.”

Scientists are using the technology to study the movements of the highly invasive blue catfish, hoping to understand the conditions that might allow them to move from one river to another — important information for fledgling efforts to control their spread.

In coming years, information from acoustic tracking may directly influence fishery management decisions.

For instance, the spring trophy season for large striped bass in Maryland and Virginia is intended to take place after most of the females have spawned. But the timing of their spawning run varies because of variables like water temperatures. Acoustic tracking could allow managers to follow the spawning run and adjust each year’s season to ensure that most fish spawn.

“Some of the regulations are not weather-dependent, but maybe they should be,” Secor said. “And that may be increasingly important, as we look at warming in the Chesapeake, to be able to make those adjustments and justify them.”

That’s not far-fetched. In the Pacific, he noted, managers use real-time tracking of some salmon and herring species and make decisions “on the fly.”

In the Chesapeake, several receivers on NOAA’s buoy network transmit in nearly “real time,” making the information from fish transmitters available to scientists almost instantly.

Meanwhile, there’s growing interest in starting a Bay fishery for cownose rays because some believe they are hurting oyster restoration and aquaculture projects. But rays have low reproductive rates — females typically produce only one pup per year — so they are easily overfished.

They also spend only part of the year in the Bay, choosing to winter off the Florida coast. No one knows whether the same rays come back to the Bay year after year or, once they get to the Chesapeake, if they stay in one particular area or move from place to another.

If a group of rays visits a tributary where there is a perceived problem and stays there, fishing might control that local population. But if different fish come to the Bay each summer, and move from tributary to tributary once here, trying to limit their impact without reducing the entire coastal population would be difficult, maybe impossible.

Last year, scientists at the Smithsonian Environmental Research Center and the Virginia Institute of Marine Science tagged three dozen rays in the Chesapeake hoping to answer those questions.

“You need to know whether you are dealing with local rays or all of the rays in the Bay,” said Matt Ogburn, a fisheries scientist at SERC. “And that is a really big question that has important implications for management.”

Search for spawning grounds

One of the major uses of the technology is to identify important habitats for sturgeon and other fish. “If we know that fish are utilizing a particular river system, or part of a river more than had previously been shown, that could allow us to work with state fisheries managers, or in a particular place where land use may have an impact on the river habitat fish are utilizing,” said Kevin Schabow, of the NOAA Chesapeake Bay Office. “It could allow us to target our efforts differently, or smarter and more efficiently.”

Biologists have yet to identify sturgeon spawning grounds around the Bay. But, by mounting receivers on boats, they can closely monitor the tagged fishes’ movements to find those areas so they could be protected.

If scientists gain enough information about the sturgeon movements, it can help in other ways. Potentially harmful activities, such as river dredging, can be done when threats to fish are minimal.

“Now, the regulatory agencies have to basically assume the sturgeon could be anyplace,” Garman said. “Telemetry has a great potential to not only understand the biology of the critter and help us to understand what the threats are, but [it also enables us] to mitigate those threats and keep the river available as a multi-user resource.”

Closing the gaps

The technology can be challenging when it comes to placing transmitters in small fish, which require smaller devices that don’t transmit as far or for as long. There can be other problems, too, as Chris Hager, a researcher with Chesapeake Scientific, learned when he tried tagging blueback herring in the Chickahominy River. Tracking showed that some of the tagged fish quickly left the river — biologists think they were eaten by blue catfish.

“Because river herring are prey for a lot of larger fish species, you never know ultimately whether you are tracking the river herring or something that ate the river herring,” Watterson said.

The technology comes with a price. Receivers cost around $1,500 each and transmitters cost several hundred dollars. But the real expense comes in maintaining the system. Receivers are vulnerable to damage — especially those in the ocean. And retrieving the data by boat is time consuming.

The Bay monitoring system still has many gaps, and those gaps get bigger along the coast where maintaining the system is difficult. Right now, there are no monitors along the North Carolina coast. In the Bay, the Navy plans to keep its system operating through 2017, but it’s unclear what will happen after that.

Though the technology has generally been in use for only a decade, and only three or four years in the Bay, scientists say its potential is huge. In various places, scientists use it to understand the impacts of pollution, the success of fish passages, triggers for spawning runs and many other questions.

Over time, they expect newer tags to help track smaller fish. Fox even believes drones will be used to fill gaps where tracking data is missing — in fact, it’s already happening in places.

Current technology, said DNR’s Stence, “will look like a ’57 Chevy compared to what we will have in a few years.”

But for now he’s pleased that in places like the Marshyhope, he and scientists can now spend their time learning the secrets of fish whose lives have for centuries been a mystery — instead of just looking for them. “Hopefully, this coming year, we will be able to shed a lot more light on them,” he said.