Horseshoe Crab Radio Tracking Station Set Up on Reeds Beach

In conjunction with Cellular Tracking Technologies (CTT) and the Cape May Part Science Center, the American Littoral Society installed on May 8 a radio tracking station and a series of nodes along the shore of Reeds in Middle Township, NJ.

This station will aid in the Littoral Society’s goal of tracking the movements of horseshoe crabs as they come back to spawn year after year. These new PowerTags are in addition to the tags the Society has been using for years that provide some basic insight on crab movement when tagged crabs are recaptured.

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.

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.

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Horseshoe crab populations in the Delaware Bay have been severely reduced over the past 30 years, largely due to harvest for bait and blood, and the loss of suitable egg laying habitat. The Littoral Society and other environmental organizations are currently seeking endangered species protection for horseshoe crabs due to their reduced numbers (as much as 90 percent below population levels in the 1980s) and their importance to the ecosystems they inhabit.
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Since Hurricane Sandy in 2012, the Littoral Society has also restored several beaches along the bay (including Reeds) so that they are suitable sites for female crabs to lay eggs.

Nine nodes have been placed along the length of Reeds Beach atop evenly spaced poles as the primary means of tracking the crabs. These nodes receive the signal from the radio tags that were glued to the shells of 25 crabs last year and then transmit it to a Yagi antenna, which picks up signals roughly parallel to the shoreline. That signal is decoded into GPS data which can be seen on a laptop.

Another antenna, called an omni, can receive a signal in a 360-degree arc, including out into the water.

Horseshoe crabs exhibit something called estuary fidelity, which is the tendency to return each year to the same estuary (bay) to spawn. However, within the same year horseshoe crabs tend to stay close to the same beach through the spawning season. The data gathered from this project is invaluable in trying to understand horseshoe crab habits around spawning and could help influence decisions on which beach habitats should be preserved.

The antenna and nodes will help us determine if the crabs tagged last year will return to Reeds Beach, which should help us gain a better understanding of how to help them.