Tracking shark populations, one shark at a time
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What is fisheries independent monitoring and how do you catch and sample sharks in Florida?
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You're listening to a group of shark researchers on a boat off the coast of Miami. They're trying to get a handle on how shark populations are doing by going out and meeting sharks in person. They just caught an eight-foot-long male bull shark using a baited buoy called a drumline. And now three adults are gently lying on top of it to hold it down on a semi-submerged fiberglass platform. A pump keeps seawater flowing past the shark's gills so it can breathe. And over the next 15 minutes or so, they measure the shark, take blood and tissue samples, count parasites, do a microbiome swab, and implant a tag, all before sliding it back in the water. The team will do it again and again, all in a field day's work for shark scientists, trying to answer how shark populations are doing.
Catherine McDonald was the lead scientist on that boat. She's a marine conservation biologist and director of the Shark Research and Conservation Program at the University of Miami. She is here to talk shark conservation and shark joy. Catherine, welcome. Thank you so much for having me. Thanks for being here. Catherine, that scene we described sounds kind of dramatic. Is that routine for you?
That's about 130 days a year of life for my team. And if we're doing it right, it's not terribly dramatic. We sample about 600 animals a year.
Wow, 600. And what kinds of information come from the blood and tissue samples, for example?
We can use those samples to answer a really wide range of questions, from questions about population genetics in species that are threatened with extinction to questions about what that tiger shark might have eaten in the last couple of days. Yeah, okay, so what kinds of species are you working with? We catch 12 species really regularly here in South Florida, and those are mostly going to be species that are coastal and subtropical. We see a lot of black noses, black tips, bonnethead sharks, which are a small member of the hammerhead family. We catch quite a few nurse sharks every year. We do see some of the species that you might catch. catch on TV, the hammerheads, the bull sharks, the tiger sharks, but our more cold water friends like the white sharks are only passing through our area.
What data do blood and tissue samples reveal about shark diets and genetics?
You said that you're looking at what they're eating. Have you found any surprises in their diet?
I'm having a good day when something doesn't surprise me on that particular day. But we did have a tiger shark vomit up a complete pig's foot on us a couple of years ago. And that one I still remember. Where did it come from? My best guess is that some of our lobster and crab fisheries here in South Florida use pigs' feet as bait. And so somebody dumping out their traps after finishing fishing probably left a treat that a tiger shark found.
What are some of the big questions that you're trying to answer? What organizes your research?
At the largest scale, shark scientists broadly are trying to answer questions about what's happening to shark populations over time. And that requires something called fisheries independent monitoring, which is what we're doing. One of the difficult things about studying fish populations, if you're relying on data from fisheries, is that the regulations for those fisheries can change or the amount of effort can change really substantially depending on the value of the fishery at a particular time.
So like the data is skewed. If if if you're trying to catch something, you might see more of something.
So if you've been fishing within that fishery for decades with a net that has a particular size mesh and then NOAA decides that to avoid bycatch or because it's going to be more effective, they want to change the mesh size. All of a sudden, your past data and your future data can't accurately be compared anymore. anymore because your method has changed.
Are there other ways to get at this besides catching them? Like, do people use camera traps like they do on land?
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Chapters
6 chapters
1
What is fisheries independent monitoring and how do you catch and sample sharks in Florida?
0:02–2:37
2
What data do blood and tissue samples reveal about shark diets and genetics?
2:37–5:41
3
Which shark species are commonly caught in South Florida and which are only seasonal visitors?
5:41–11:25
4
How do researchers distinguish real population changes from increased detection (drones, cameras)?
11:25–15:08
5
What are the long-term trends for shark populations in Florida and which species are recovering slowly?
15:08–18:32
6
What surprising behaviors did your lab document about remoras and manta rays (cloacal diving)?
18:32–18:33
Speakers
2 identifiedMore from Science Friday
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