The secret lives of striped bass: scientists study a unique population of the 'golden retrievers' of the sea
How much anesthesia does it take to put a fish under before surgery?
It’s not a question most veterinarians have to answer, but it’s what Lisa Abbo was trying to figure out at the Marine Biological Laboratory in Woods Hole as she looked down at a striped bass on a steel operating table.
“We want him or her to be out enough to be able to do the procedure and have the fish not feel as much, but we also don't want to have the animal go too deep,” Abbo said. “So we're kind of weighing that fine line.”
The fish, almost three feet long, with silvery scales and eight olive-colored stripes lengthwise along its body, occasionally tried to wiggle away as she made a short incision on its belly. Once she cut through the muscle, she inserted a 3-inch-long, black transmitter inside its body cavity near the stomach. The device will allow scientists to receive a signal telling them when a striper enters and leaves a coastal pond in Woods Hole.
So, what was going through her head during the procedure?
“Uh, don't mess up,” she said with a laugh. “All the organs and everything are kind of pushed up there. So I'm just trying to be gentle.”
This salt-water pond in Woods Hole village has become something of a summer resort for a group of three to four dozen striped bass. The fish that come year after year seeking shelter and a steady supply of food are a delight for visitors who’ve come to know them.
But for one MBL biologist, Steve Zottoli, they began to represent more: a unique opportunity to understand why stripers do what they do in the wild.
“We have an experimental area that's unique. It's an enclosed pond and it only has a narrow entryway or exit. So we can tell whether the fish is in the pond, or not in the pond,” Zottoli said. “We can tell when the fish leaves because we don't get the signal. We can tell when it comes because we get the signal.”
With this realization, he decided to do something that’s never been done before: track individual stripers in the wild year after year.
“To my knowledge,” he said, “no one has ever been able to do it quite like that, with a group of fish, and know how they are acting individually or otherwise.”
This fall, they’ll insert transmitters into 20 stripers, adding to a group of 15 fish that they’ve tagged in past years. Soon, these stripers will leave the pond to migrate south, a journey that will force them to face new challenges as their species seems to be in decline.
The study is allowing Zottoli to ask questions like: When exactly do they leave? Do they travel together or separately? And when they leave, where do they go?
Of course, answering these questions means his team has to successfully insert the transmitters. So after the first fish is stitched up, alert, and returned to the water, it’s onto the next. Luckily for the scientists, the stripers aren’t hard to catch; a quick drop of squid in the water brings a flurry to the surface.
“They're the golden retrievers of fish,” Zottoli said. “They’re opportunistic feeders. They like to eat and they'll find a situation where they can get food.”
In seconds, the next fish is reeled in and lowered into a cooler filled with a green bath of anesthesia. Once again, the veterinarian is monitoring the striper’s reaction carefully. And after just a few moments more, the fish starts to lose its balance.
“So you can see it’s upside down, and then progressively, it will lose its ability to move, to swim,” Zottoli said.
Along with inserting the transmitter, the team also takes a tissue sample and puts a plastic ring through the tail to alert fishermen that the fish is part of a research study.
“How else would they know that we had tagged the fish and that there was something inside?” he said.
This work is fed by Zottoli’s passion. In the last seven years working with the fish, he’s recruited not just other scientists, but teenage interns who’ve studied the fish’s unique stripes. He details much of their work and other striped bass facts on his website: www.StripedBassMagic.org.
“One high school student did some control experiments in the aquarium to make sure the fish patterns don't change on their own, and they don't,” he said. “And then [the student] checked to see if we could identify, from year to year, fish that come back—just by those aberrations. And indeed, you can.”
It means those stripes on the side of a fish are like fingerprints: each fish can be identified as an individual.
The culmination of this work has allowed Zottoli to answer some other big questions. Now he knows that each striped bass seems to leave the pond at a different time for its winter migration, which changes how scientists think about schooling fish.
Other questions remain, but on a day when a not-yet-anesthetized striper is thrashing up against the roof of a cooler in a bid to escape—“It’s like Jurassic Park!” Abbo said—there’s not much room to be so forward-looking.
Right now, it’s one fish, one transmitter at a time.
More information about striped bass, what scientists are learning, and how students can contribute can be found at www.stripedbassmagic.org.
Correction: An earlier version of the story stated a 3-inch-long transmitter was inserted inside the striped bass's stomach. That is incorrect. It was inserted inside the fish’s body cavity near the stomach.