November 22, 2013
In 1997, Dave Secor was a young fisheries biologist just starting his career at the University of Maryland. Like almost everyone else, he believed that Atlantic sturgeon, a species that has survived since the age of the dinosaurs, had been long gone from the Chesapeake Bay. But that year a small number of juvenile sturgeon turned up, and they were too small to have immigrated from elsewhere.
"That was a major surprise," Secor said.
Though sightings were rare back then and still are today, the population of sturgeon that spawn in the Chesapeake Bay has grown. In 2012 that population was added to the endangered species list. Usually a listing is bad news, but in this case it was cause for celebration.
Now scientists are racing to find out what's driving the recovery so they can reinforce it. Their efforts recently got a big boost when NOAA Fisheries awarded a three-year, $1.75 million species recovery grant to the Maryland Department of Natural Resources and the Virginia Department of Game and Inland Fisheries.
Atlantic sturgeon were prized for their flesh and for the caviar made from their roe. But fishing for them in the Chesapeake peaked in the 1890's, and no one alive today has seen a healthy run of sturgeon in the Bay. Even basic information about their life history was forgotten long ago, and this is a problem for the scientists working to protect them.
"We need to find out where they're spawning so we can protect that habitat," Secor said. Scientists also hope to locate their nursery grounds and to identify the biggest threats to their recovery. Ship strikes and poor water quality are among the top suspects.
"This recovery may be part of a cycle," said Secor. "If we don't pursue this now, we may not see it again for another 20 or 30 years."
A Fish That's Hard to Follow
But finding their spawning grounds is difficult, not least because there are so few of them out there. To solve that problem, scientists will use the new funding to tag about 240 sturgeon with acoustic transmitters. That will allow scientists to track their movements in the Bay.
Atlantic sturgeon spend most of their time at sea, travelling up and down the shelf break where they plow the bottom with their snouts, eating worms and crustaceans. Like salmon, they return to their natal streams to spawn.
Unlike most salmon, however, which spawn once and die, sturgeon make the spawning run repeatedly. They can live up to 60 years and can grow up to 14 feet (4.3 meters) and 800 pounds (370 kg).
Matt Balazik, a postdoc at Virginia Commonwealth University, is doing most of the tagging. The acoustic tag, about the size of a Sharpie marker, is inserted into the belly of the fish through a small incision. The minor surgery takes less than five minutes, and the unharmed fish are quickly sent on their way.
The tag emits a coded sound roughly once a minute, a signal that's recorded whenever the fish passes within range of a receiver. Each tag has a unique acoustic signature, allowing scientists to track individual fish.
"You can think of the tag as like an EZPass," said Matt Balazik, referring to the device that motorists in the Northeast attach to their windshields, "and of the receivers as toll booths."
An acoustic signal is used because sound waves travel well underwater. Radio waves would dissipate quickly in the murky Bay.
Collaboration is Key
Scientists have tagged sturgeon all along the Eastern seaboard, but the Chesapeake is uniquely difficult because it's a meta-estuary-an estuary comprised of many smaller estuaries-and it's the largest one in the nation.
"In the Hudson it's a piece of cake," said Dave Secor. "A few receivers bank to bank and you've got the river covered at that point." The mouth of the Chesapeake, on the other hand, is 20 miles wide.
But the tagging project got a big boost from the Navy, which recently installed an array of 58 receivers, most attached to Coast Guard buoys, throughout the mouth of the Chesapeake Bay.
The Naval Base at Norfolk, Virginia is the largest in the nation, and it's one of several naval installations in the lower Chesapeake Bay. As a federal agency, the Navy is required to minimize interactions with endangered species.
"We want to know where and when sturgeon are utilizing the Bay," said Carter Watterson, a Navy biologist. "Once we know that, we can work to minimize any impact we have on the species."
The Navy will benefit from the tags that Maryland and Virginia researchers deploy because they increase the value of the receiver array. And the state researchers will benefit every time Watterson sends them tracking data on their fish.
The buoys the receivers are attached to also record environmental data, allowing scientists to correlate sturgeon activity with ocean conditions. This will be key to understanding how those conditions affect the fish, and in particular how sensitive the fish are to the low oxygen levels that plague the Bay every summer.
A Living Fossil
Sturgeon have existed in pretty much the same form for at least 85 million years. A living fossil, they survived the meteors that killed off the dinosaurs and many other catastrophes since. "They're designed to handle anything," Matt Balazik said. "Except humans."
But don't write them off just yet. "The fact that they're still hanging in there makes me a bit more optimistic than I was earlier in my career," said Dave Secor, the biologist who was surprised to see juvenile sturgeon in the Chesapeake Bay in 1997.
"What sturgeon have taught me as a scientist," he said, "is that sometimes it can be delightful when you're wrong."