Tagging Horseshoe Crabs on Fishers

by Jane Ahrens

This spring, during the spawning season, Science Teacher Carol Giles and her team of volunteers tagged horseshoe crabs on Fishers Island. Carol is a trained site coordinator, helping to collect data on horseshoe crab spawning, abundance, size, sex, and tag returns. The data collected through this program is used to assess the status of horseshoe crabs in New York State, and will help determine the management and conservation of this important species throughout the region.

This tagging program is conducted under the authority of the Fish and Wildlife Act of 1956. It is coordinated by Cornell University Cooperative Extension’s Marine Program, working with the New York State Department of Environmental Conservation to develop and organize the New York horseshoe crab monitoring network.

Half an hour before high tide, on twelve evenings around both the full and new moons in May and June, the dedicated volunteers met at Dock Beach – this often occurred between 9pm and midnight. With bug spray and flashlights in hand they waded into the shallow water to find the horseshoe crabs that had come in to mate. In all, fifty horseshoe crabs were tagged with numbers between 311201 – 311250, and over the 12 nights, they counted hundreds of horseshoe crabs of various sizes. (Tag # 311201- 311225 were tagged on 6/11/14.  Tag # 311226-311243 on 6/25/14.  Tag # 311244-311250 on 6/27/14.) It will be interesting to see if they return to Fishers for future breeding!

Many thanks to all the volunteers who lent a hand including teachers Tawnya Eastman and Jared Kaplan, Rob and Karen Goodwin, Chris and Kathy Dollar, Greg and Anne Marie Thibodeau, Karen Tirabassi, Gail Cypherd, and Gina Scumaci; students Craig Mrowka, Jack Morrissey, Ian Tirabassi, AJ Eastman, Emma Cypherd, Noah Cypherd, Molly Cypherd, Constance Toldo, Fred Toldo, Amber Ferguson, Arrianna Suarez-Reyes, John Biaz, Lydia Doucette, Christina Toldo, Ian Tirabassi, Wyeth Bonser, Ben Weber, Andrew Edwards, Will Swenson and Grant Swenson; and FIS alumni Ken Edwards, Lori Edwards Swenson and Whitney Edwards.

If you find a tagged horseshoe crab, or even just the tag, please take a moment to complete and submit this form:
Horseshoe Crab Resighting Form

About Horseshoe Crabs
from eol.org/ Encyclopedia of Life

Horseshoe crabs are typically active at night, with activity peaking around the time of the full moon. They dig for food, such as worms, algae and molluscs in the sediment. During the spring and summer, adults migrate in huge numbers towards sandy beaches and congregate in the shallow water. Breeding is associated with the lunar and tidal cycles, with most adults arriving at the full or new moon and within a couple of hours of high tide. The direction of the waves guides the females towards the beach. Males patrol along the bottom of the beach in the shallow water, waiting to intercept beach-bound females.

Pairs make their way to the high tide mark and the male fertilises the eggs as they are laid into a 15 centimetres deep nest in the sand. From 2,000 to 20,000 eggs may be produced in a single clutch. Very often there may be more than one male accompanying each female; in some cases there have been as many as 14 males to one female. As the tide begins to retreat, the horseshoe crabs make their way back to the sea. 

The sticky eggs hatch after around five weeks, but this is dependent on temperature. The larvae, which are known as ‘trilobite’ larvae may remain buried in the sand in aggregations for a number of weeks before emerging at high tide. After they enter the water, they undergo a ‘swimming frenzy’ of constant, vigorous activity. Six to eight days after emerging, they moult into the first juvenile stage, which is very similar in appearance to the adult stage. At this point they cease swimming and start to live on the bottom.

Horseshoe crabs are slow-growing. Males reach sexual maturity at 9 to 11 years of age and females between 10 to 12 years. Although it is difficult to assess age in this species, the average life-span is thought to be 20 to 40 years. The horseshoe crab is an essential part of the ecosystem in which it occurs. Their eggs provide a valuable source of food for many species including wading birds, sea turtles, alligators and fish. Furthermore, the action of the crab as it ploughs the sea bed in search of food aerates the substrate, resulting in a higher level of species richness.

Featured Photo

USCG Eagle passing the Race early morning March 18, 2023 on her return from the Chesapeake Bay . Photo Credit Marlin Bloethe

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