For the first time, horseshoe crabs in the Indian River Lagoon will be tracked with acoustic tags that monitor their movements and behavior. Monitoring animal movement with acoustic tags can provide data that helps manage the ecosystems those animals inhabit.

The Indian River Lagoon hosts the largest concentration of nesting horseshoe crabs in Florida. The large congregation of crabs made it an ideal location for a tagging project of this kind. The acoustic tags do not harm the animals, and similar to a GPS device, track their movements in the water and send the detailed data to scientists.

Since 2019, volunteers with the Horseshoe Crab Citizen Science Project have tagged horseshoe crabs in the lagoon with numbered tags that don’t transmit movement data. In 2021, 41 volunteers counted 73,709 horseshoe crabs and tagged 1,567. Beachgoers can call in and report sightings of tagged crabs when spotted on the beach, but data is limited to which animals are spotted and reported and does not give information about how far the animals travel.

“Acoustic tagging helps monitor their movements in the water, so we don’t have to rely on people,” said Holly Abeels, UF/IFAS Extension and Florida Sea Grant agent who is part of the project. “Our citizen science project is wildly successful, but these acoustic tags will give us a whole new look into how these animals move. We will learn where they travel and when they are coming in and out of the bay. Right now, we don’t really know once they leave the beach where they travel to.”

Knowing animal movements will also help make conservation decisions that help the species and the lagoon.

For example, the data gained from tracking the horseshoe crabs can guide the placement of wave attenuation devices (WADs) in the lagoon. These hollow, pyramid-shaped concrete devices dampen strong waves before they hit the shoreline to minimize erosion, but could interrupt horseshoe crab traffic if not properly placed and minimize impact to the horseshoe crabs’ natural movements and behaviors.

Additionally, better understanding the movements and behavior of the animals will provide further insight for the Florida Fish and Wildlife Conservation Commission, which monitors and manages horseshoe crab populations around the state.

“Horseshoe crabs are important members of the intercoastal ecosystem,” said Berlynna Heres, Florida Fish and Wildlife Commission researcher working on the project. “They are integral to the environment and losing them would have cascading effects. If we lose horseshoe crabs, we lose a food source for many nesting shorebirds and other wildlife, so it’s important for us to maintain our biodiversity and conserve the populations we have.”

“We don’t know a lot about horseshoe crab behavior beyond their breeding habits,” said Heres. “This will help us learn more about their other activities when they are not on shore to breed. The more we learn about what they’re doing when they’re not spawning, the better equipped we are to make decisions and improvements that support their populations.”

Fifteen crabs will be randomly selected for tags. The monitor batteries have a lifespan of roughly 16 months and will provide data throughout that time. The tags will remain on the crabs after they are no longer active but pose no risk to the health of the animals.

This project is managed by the Florida Department of Environmental Protection and funded by one of the department’s Citizen Support Organizations: Friends of the Spoil Islands. Florida Fish and Wildlife Conservation Commission, UF/IFAS and Florida Sea Grant are partners of the project.

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