Counting Horseshoe Crabs to Save Them
A horseshoe crab floats by the shore on Union Beach in New Jersey. The species is listed as Near Threatened by the International Union for the Conservation of Nature. (Photo: Peter Massas, Flickr CC BY-SA 2.0)
Horseshoe crabs are important in the Atlantic ecosystem, and also in medicine. They are an ancient species but lately in decline. Reporter Karen Zusi profiles a Massachusetts Audubon Society tagging program that will provide an accurate census and reliable information to understand how many can be safely harvested.
CURWOOD: It’s Living on Earth, and I’m Steve Curwood. For healthy oceans, it’s not enough to protect just the top of the food chain – the cod or halibut or swordfish we eat. The bottom of the food chain is vital too. That could be the plankton or the tiny forage fish eaten by many species – or it could be the extraordinary prehistoric-looking horseshoe crab. These helmet-shaped arthropods have been around for millions of years, and up and down the east coast of the US, volunteers come out to count them as the females come ashore to spawn. And on Cape Cod, as Karen Zusi reports, scientists and volunteers are tagging and labeling the crabs to help conserve them.
[SOUNDS OF WAVES AND BIRDS]
ZUSI: There are a lot of reasons why someone might appreciate the lowly horseshoe crab. Eel and conch fishermen use them as bait, and medical companies draw blood from the animals. Horseshoe crab blood will clot in the presence of bacteria, so these companies can use the crab’s blood to make sure vaccines and medical implants are free of germs. Their blood is worth sixty thousand dollars a gallon.
ZUSI: But horseshoe crab populations are dropping. To preserve them, scientists and volunteers on Cape Cod are wading into the water to count and tag the animals. Special labels help them keep track—Mark Faherty, the science coordinator at Audubon’s Wellfleet Bay Sanctuary, describes the standard process.
FAHERTY: The way that you apply the tag seems sort of barbaric, but according to research that’s done, it doesn’t seem to hurt the crab. You drill a hole through the corner of their shell and then you use your thumb and put this tag on, and they stay on, and uniquely identify that crab. And that data’s used by researchers to estimate crab movements, crab survival, how they’re using the spawning beaches, that kind of thing.
ZUSI: The Massachusetts Audubon Society just recruited graduate student Michael Long to lead their newest horseshoe crab study. With researchers from the University of Massachusetts, he will be tagging the crabs this summer with a telemetry label instead, glued onto the crab’s shell.
FAHERTY: My acoustic study is going to be putting on acoustic receivers out in the bay, and acoustic markers on the crabs. The receivers have about a 600-meter detection radius so anytime a crab that’s marked with an acoustic receiver comes within 600 meters of that receiver, it will mark where it is. So based on where each crab pings you can kind of track its movements around the bay. And you can’t beat living out on Cape Cod during the summer.
ZUSI: None of this would be possible without the Audubon Society’s volunteers. They come from all walks of life, but they have a few things in common—as the science coordinator, Faherty should know.
FAHERTY: Good people. Good, honest, conservation-minded people who have nothing better to do. We get a lot of retired teachers or retired professionals who still have a lot of energy, and they want to do stuff.
ZUSI: At an Audubon horseshoe crab conference, Long organizes new volunteers to help him count horseshoe crabs on the beach, and Faherty trains them in the basic survey procedures. The training session was supposed to be on a real beach, but after some flooding, Faherty elected to stay on the edge of the marshes. And it let the volunteers get a close-up look at some other wildlife.
[CHATTER, MULTIPLE VOICES] Look, red fox! Wind direction… Red fox sighting! How pretty! Wow. I see them daily where I live. Has he—has he got a vole? Probably. Meadow vole? He’s so completely nonplussed by us. Look, it’s nature at a nature sanctuary. It’s gone. “Oh, look, a human.”]
ZUSI: Once they got down to business, the volunteers were trained to divide the beach into small sections, count the horseshoe crabs, and record all of their information. The volunteers go out to survey when female crabs are coming to lay their eggs in the sand. Males follow to fertilize the eggs after they’re laid.
FAHERTY: The male crabs you quickly learn to recognize because they’re by themselves. They will mate with a model, if you make a model of a horseshoe crab—the males will congregate around it. They’ll spawn. They’ll spawn with your boot. These are just hormonally-charged animals that are ready to mate with anything. Females are not lonely for long in the horseshoe crab world.
FAHERTY: All right, you’re trained! [LAUGHTER] Go forth and survey! It’s official.
ZUSI: Karl and Judi Goldkamp, a retired couple from Orleans, are two of these Audubon volunteers. They’ve helped with everything from frogs to turtles, but the horseshoe crab is special.
KARL GOLDKAMP: For me, it’s a surprise. You know, if you don’t know this, and you go, “Holy cow! You know, who knew that there were that many horseshoe crabs that actually met at the beach and had this function to do?” If you weren’t exposed to that, you realize that it is here and now that nature is happening. There is a real window. They know it, and it’s all timing. It just takes you out of wherever you are. You gotta to be there to watch it or you miss it.
JUDI GOLDKAMP: But they have a great use. They’re needed for medical uses, but then you also have harvesting for bait and both are necessary. So part of it is--how do we get all this to work together, and keep the supply of horseshoe crabs at the maximum that you can, with allowing all the different uses of it? So. [Karl] That’s why you’re doing it? I thought you did it because I dragged you into it. [Judi] That’s part of it too. [LAUGHTER]
ZUSI: With all of this information, and the help from their volunteers, scientists hope to figure out how many horseshoe crabs can be harvested sustainably, and from where. The research will help state wildlife regulators set limits on harvest, and ensure that the horseshoe crabs are around for generations to come. For Living on Earth, I’m Karen Zusi in Wellfleet.
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