Tag You’re It! An Update on the Radio Tag Horseshoe Crab Study

Female horseshoe crab with US Fish and Wildlife Service Tagging Program button tag and CTT radio tag at Reeds Beach, Cape May County, NJ.

​In May of 2023, our partnership with the Cape May Point Science Center (CMPSC) began, which allowed us to team up with Cellular Tracking Technologies (CTT) to take our horseshoe crab research to the next level.

Our goal is to track the behavior and movement patterns of horseshoe crabs during the spawning season. To gather this data, tags which transmit radio telemetry data were affixed to the horseshoe crab’s shell. Whenever these tagged crabs came ashore, the time and beach location were tracked and recorded.
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The Delaware Bay is home to the largest population of spawning Atlantic horseshoe crabs, (Limulus polyphemus). The horseshoe crabs come ashore to spawn and lay eggs during the months of May and June, with peak spawning occurring during new and full moon events at high tide.

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A female horseshoe crab can lay up to 4,000 eggs at a time, and up to 80,000 eggs per season. Horseshoe crabs are keystone species, playing a very important ecological role. Migratory shorebirds, like the threatened Red Knot, (Calidris canutus), use the Delaware Bay as a stopover during their migrations from the tip of South America to the Canadian Arctic. They rely heavily on the easily digested fats and nutrients found in horseshoe crab eggs to regain weight and fuel their continuing migration.

Working closely with CTT to kickstart this pilot study, 25 horseshoe crabs were equipped with cellular tracking devices at Reeds Beach in Middle Township, NJ along the Delaware Bay. A station was installed at a house adjacent to the beach, which would serve as the main hub for receiving the data. Heading south, five nodes were installed along the high tide line at Reeds, Cooks, Kimbles, and Pierces Point beaches.  The nodes receive signals every time a tagged horseshoe crab comes ashore near them, which is then sent to the main data hub at Reeds Beach.

Preliminary data has shown horseshoe crab activity on beaches around high tide with tagged males coming ashore more frequently than females. Of the 25 tagged crabs, 17 of them have resurfaced again. While the tagged female crabs only resurfaced once or twice after tagging, the males were much more active – one male was detected on the beach 10 different times. One of the tagged female crabs moved 500 meters south from Reeds to Cooks Beach from one night to the next!

On July 4, 2023, a big storm event took place which completely knocked the station down, putting a temporary halt to our data collection.
 
We are currently working on analyzing the data from 2023 and planning for the year to come. We look forward to further incorporating the use of radio tags in our horseshoe crab tagging program, as well as working to help bridge gaps in horseshoe crab science with CTT and CMPSC!
 
The addition of radio tags to the horseshoe crab tagging program was made possible thanks to our gracious donors, Rob and Wendy Wilson.

The Littoral Society continues to fight for the protection of horseshoe crabs, while working to restore spawning habitats.
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Our annual monitoring effort includes collecting data for use in assessing movement and behavior in horseshoe crabs, along with gauging our habitat restoration success and supporting the U.S. Fish and Wildlife Service’s Cooperative Tagging Program.