Scientists say that the water in Boston harbor is getting cleaner, leading to an increase in the number of sand tiger sharks using the area as a nursery habitat.
ARI SHAPIRO, HOST:
There have been lots of sightings of great white sharks off the coast of New England this summer, and there are other species of sharks swimming in the waters too, including in Boston Harbor. As Craig LeMoult of member station GBH reports, scientists say those sharks deserve our attention as well.
(SOUNDBITE OF FISHING LINE REELING)
CRAIG LEMOULT, BYLINE: Ryan Knotek, a research scientist with the New England Aquarium, grips a fishing rod as his line is pulled.
(SOUNDBITE OF WATER SPLASHING)
RYAN KNOTEK: Come on up. Come on up. Come on up.
(SOUNDBITE OF FISHING LINE REELING)
LEMOULT: He’s caught a sand tiger shark.
EMILY JONES: Come on.
LEMOULT: As he pulls it up alongside the boat, his colleague Emily Jones scoops it into a net, and it’s bigger than they expected.
MIKE O’NEILL: Oh, my gosh.
JONES: Oh.
KNOTEK: OK, that’s the biggest sand tiger we’ve ever had.
LEMOULT: It’s still a juvenile, but it’s about 4.5 feet long with a mouthful of teeth. The team from the aquarium is here to surgically implant tags in sand tiger sharks that put out a signal that can be picked up by receivers on buoys up and down the East Coast, allowing the scientists to track their movement.
(SOUNDBITE OF WATER SPLASHING)
KNOTEK: I got it.
JONES: All right.
LEMOULT: Knotek gets the shark into a cooler full of water, and it thrashes around at first. But once it’s flipped onto its back and held by Mike O’Neill of the aquarium, the sand tiger gets totally calm. It’s a behavior called tonic immobility.
JONES: Interesting evolutionary thing, but convenient.
KNOTEK: Very convenient for scientists.
O’NEILL: Yes, awesome for science.
LEMOULT: Jones gets a syringe ready.
JONES: This is the local anesthetic, just to numb the area.
LEMOULT: Knotek uses a scalpel to make an incision in the shark’s abdomen, and he squeezes in the tag, which looks a bit like a tube of lipstick.
(SOUNDBITE OF SCALPEL SLICING)
LEMOULT: Sand tigers can grow to more than 10 feet long, but they only come up to Massachusetts waters in the summer as juveniles. They don’t come to the surface much, so most people don’t even know they’re here. And they’re only interested in fish, so they don’t pose a risk here to humans. Once Knotek has sewn up the incision with surgical precision, he releases the shark back into the harbor.
(SOUNDBITE OF WATER SPLASHING)
JONES: Bye.
KNOTEK: Adios.
JONES: Wow. that was awesome.
O’NEILL: Nice. Nice.
KNOTEK: Good work, everybody.
O’NEILL: Great job.
LEMOULT: Over the decades, the population of sand tiger sharks was decimated by fishing.
KNOTEK: And that fishing pressure between, like, the ’70s to the ’90s actually depleted their population by, like, 70- to 90%.
LEMOULT: But then catching and keeping them was outlawed in the ’90s.
KNOTEK: So for the better part of two decades now, sand tigers have been protected, and we are optimistically starting to see some signs of recovery.
LEMOULT: This is a conservation success story in the works. The waters here are far cleaner than they used to be, and an increase in bait fish is now drawing sand tigers in to use Boston Harbor as a nursery area. It’s a slow progress. Knotek says about 1- or 2% of the population is restored a year.
KNOTEK: And the goal is to tag as many of these sharks as we can to just figure out exactly when, where and why the sharks are in Boston Harbor, with sort of that end goal to maybe get some additional actions towards protections for this species as they try to recover.
(SOUNDBITE OF WATER SPLASHING)
KNOTEK: Oh, I think it’s been tagged.
LEMOULT: Knotek catches another sand tiger, but this one they’ve met before. The New England Aquarium team tagged it here last summer.
KNOTEK: That thing traveled hundreds of miles down to – who knows? – Carolinas or Florida and came back to this exact marsh. It’s nuts (laughter).
O’NEILL: That’s demonstration of how massive the ocean is and how small it can be…
KNOTEK: Yeah (laughter).
O’NEILL: …Sometimes – when people think about our impact on it.
LEMOULT: The presence of great white sharks in New England waters is more talked about, Jones says. But…
JONES: There’s a lot more sharks out there in New England than just the white sharks, and it’s really important that those sharks get attention and funding to gather data ’cause we just don’t know a lot about them yet.
LEMOULT: The sand tigers will stick around Boston Harbor until September before heading back south. And the batteries in the tags they’re carrying can last up to 10 years, giving scientists a window into the behavior of this slowly rebounding species. For NPR News, I’m Craig LeMoult in Boston.
(SOUNDBITE OF SOULS OF MISCHIEF SONG, “93 ‘TIL INFINITY”)
Copyright © 2025 NPR. All rights reserved. Visit our website terms of use and permissions pages at www.npr.org for further information.
Accuracy and availability of NPR transcripts may vary. Transcript text may be revised to correct errors or match updates to audio. Audio on npr.org may be edited after its original broadcast or publication. The authoritative record of NPR’s programming is the audio record.
