Horseshoe Crab Monitoring

American or Atlantic Horseshoe Crab

(Limulus polyphemus)

Join volunteers with Save Coastal Wildlife (SCW) nonprofit to help count and tag mating horseshoe crabs along the shores of Raritan Bay and Sandy Hook Bay, the northern bayshore region of New Jersey.

Since 2009, volunteers with Save Coastal Wildlife and the Bayshore Regional Watershed Council have been monitoring horseshoe crab spawning activity. Volunteers walk a bayside beach at several sites during the same time to count the number of crabs present. Volunteers also tag single crabs to keep track of their whereabouts and movements within New York Harbor and to find out how many horseshoe crabs have already been observed as part of our ongoing effort to understand the mysterious life of a 400 million old species, an ancient mariner.

It’s exciting work that is contributing to long-term research and helping people to better understand and protect horseshoe crabs, especially those that live in urban-suburban waters along the east coast of the United States, including New York Harbor.

A cluster of male crabs surrounding a female in hopes of mating with her.

A cluster of male crabs surrounding a female in hopes of mating with her.

Save Coastal Wildlife and the Bayshore Regional Watershed Council are working with the U.S. Fish and Wildlife, the National Park System, and New Jersey Department of Environmental Protection, Division of Fish and Wildlife to to coordinate and implement this project.

But we need your help! We cannot do this alone. We need interested and thoughtful people to help. We encourage participants to get involved with our annual horseshoe crab monitoring program in the spring.

Training usually takes place starting in April of every year. All volunteers will be trained. During a training session, people will learn how to record data and tag horseshoe crabs for an upcoming project.  Trained volunteers will monitor horseshoe crabs on full moon and new moon evenings the following May and June.

Save Coastal Wildlife members depend on citizen volunteers of all ages to help count, tag, measure and return horseshoe crabs to the water.

Join volunteers with Save Coastal Wildlife

Spend an evening on a bayside beach in search of mating pairs of Atlantic Horseshoe crabs!


All new volunteers are expected to attend a training session before helping to count or tag horseshoe crabs in the field during May and June.

Training takes place during late April.

The location is usually the Bayshore Waterfront Park in Port Monmouth, NJ.


Training for Horseshoe Monitoring usually takes place at the Bayshore Waterfront Park. Address: 719 Port Monmouth Road, Port Monmouth, NJ 07758






Current Monitoring Locations


Sandy Hook, Gateway NRA at Plum Island.

Address: Parking Lot B, Hartshorne Road, Highlands, NJ 07732. Volunteers please meet at Parking Lot B near the Bathroom Pavilion. Beach Captains: Laura Bagwell & Shannon Evens


Mouth of Many Mind Creek in Atlantic Highlands.

Address: Gravel parking lot near 10 Simon Lake Dr, Atlantic Highlands, NJ 07716. Volunteers please meet in gravel parking lot at the end of First Avenue located on the side opposite the marina. Beach Captains: Joe Reynolds & Joe/Robin Sheridan and family


Leonardo Beach in Middletown Township

Address: near 218 Beach Avenue, Leonardo, NJ 07737. Volunteers please meet on the beach near the parking lot at the end of Beach Avenue located near the Leonardo state marina. Beach Captains: Sue Provost & Donna MacDonald


Keyport Harbor in the Borough of Keyport

Address: On-street parking near 50 Cedar Street, Keyport, NJ 07735. Volunteers please meet at the northern end of Cedar Street, located next to Cedar Street Park. Cedar Street can be accessed via 1st Street or Pine Street in the Borough of Keyport, not far from the Keyport/Union Beach border and Chingarora Creek. Beach Captains: Ron Dente & Paul Mandela


Cliffwood Beach, Aberdeen Township

Address: Entrance to beach parking lot located near 625 Ocean Blvd, Keyport, NJ 07735. Volunteers meet inside the parking lot nearest the beach located on Ocean Blvd, situated on the border of Aberdeen Township and Old Bridge Township. *** Please note that some access roads to this site via Cliffwood Beach may flood during high tide events. For safety, please access this site via Old Bridge Township from US Route 35 and Raritan Blvd and Ocean Blvd. Beach Captains: Christine Balint & Frank Huza



Basic Protocol to Monitor Horseshoe Crabs



VERY IMPORTANT: Never do anything you feel uncomfortable doing.

Arrive at the designated beach site at least 30 minutes prior to the scheduled time to meet the Beach Captain(s). The Beach Captain will provide volunteers with specific instructions for your location. You will be surveying in a group. No individuals! 

Watch where you step!  Sometimes female or mating horseshoe crabs bury themselves deep in the sand while laying eegs.

Watch where you step! Sometimes female or mating horseshoe crabs bury themselves deep in the sand while laying eegs.

NO RUNNING!! Especially in the dark. Take your time. Please be mindful of large rocks, bricks, buckets, driftwood and other objects on the beach that might cause you to trip and fall. Please be careful and mindful of your surroundings. Always think safety first!  

NO BARE FEET! Shoes are a necessity.  We recommend rubber boots, waders, hip boots, water shoes, or old sneakers.  A good pair of waterproof boots is preferred for May monitoring dates when water temperatures are still chilly.
Don't forget to dress for the weather. Dress warmly, but also wear something to get dirty and/or wet. Work gloves may be useful to hold crabs. Bring a headlamp or flashlight.  Headlamps are useful because they free up both hands to carry items. 

Consider using insect repellent at night. It can be buggy along a bayside beach during dusk and twilight hours.
Volunteers under the age of 18 must be accompanied by an adult.  Children, scouts, or students under the age of 18 must be accompanied by a parent, teacher, scout leader, or a legal guardian.
IF THUNDERSTORMS ARE PRESENT, OR CONDITIONS ARE UNSAFE, DO NOT GO ONTO THE BEACH. A beach captain will determine if the survey should be cancelled or continued later that same evening.


Lots of stuff can be found living on horseshoe crabs

Drawing by Susan J Draxler

Protocol to Tag HSC


The following text describes the protocol when attaching plastic button tags (Beach captains at each site will have alcohol, cotton swabs, and antiseptic solutions to carry out this system):

Only single crabs will be tagged. Never tag crabs that are in pairs or clusters. Crabs will only be selected for tagging activities within the monitoring area or transect zone on the beach after the crab has been counted or surveyed by an observer. 

Attach only one tag per animal.  If the animal is damaged near the attachment area, do not tag the animal.

1. Tags will be attached to the left posterior (rear) point of the prosoma (first section of body).  There is a high concentration of fibrous material within the body in this area, which minimizes bleeding.  Before drilling the attachment hole, clean off any epibionts (barnacles, etc.) near the attachment site.
2.USFWS (US Fish & Wildlife) recommends first cleaning the area where the hole will be drilled by rubbing the spot with alcohol.

3.Next the drill should be dipped into a Betadine antiseptic solution to disinfect the drill before making the hole in the shell (prosoma).

4. The tag is attached by drilling a 5/32" hole (7/64” for small tags) through the left side of the prosoma near the dorsal edge and then pushing the plastic pin (with tag) into the hole as far as it will go (it should NOTgo all the way through the prosoma and come out the other side).

5. This procedure should be repeated for every individual that is being tagged.

6. All tags will be used in consecutive sequential procedure. One number after another.

7. Any crabs found with tags already attached to the shell are to be reported to the Beach Captain and recorded on the re-sighting form.
If you plan to tag crabs, please bring a cordless drill with tape on a 5/32-inch drill bit up 1/8" from the tip to tag the crabs. Also, we will need measuring tape and rulers that measure in millimeters. Bring plenty of clipboards, pens/pencils, flashlights or headlamps.


Protocol to Conduct Spawning Survey

Surf Line: The point offshore where waves and swells are affected by the underwater surface and become breakers.

Surf Zone: The zone within which waves approaching the coastline are breaking.

The following text describes the methods on how to count horseshoe crabs or conduct a spawning survey on the edge of a bayside beach.

When you visit your chosen beach area on the designated date, the beach captain will split volunteers into two teams consisting of: 1) a team for transect-based count horseshoe crab spawning survey; 2) a crab tagging team consisting of at least one trained tagger.


Bring a clipboard or a hard surface to write on.  Also bring a couple of pens or pencils.

You will be surveying in a group with at least two people. No individuals.

Each beach will be sampled along a transect of 1,000 feet in the surf zone along an estuary. 

1. As you walk to the starting location find a stick (1 to 2 ft. long) that you can use to determine high tide. When you get to the starting location, stand the stick in the sand at the tide line. The tide line is the highest point on the beach that the water reaches. Move the stick up the beach as the water reaches higher on the beach. Begin the survey when the tide begins to recede and the water no longer reaches the stick. Record your starting time on the Beach Site Sheet where it says START OF SURVEY.

2. The “horseshoe crab line” you will follow is not a straight line and may be above or below the water line or the surf zone - typically the area where the waves break and wash over the horseshoe crabs, especially males seeking females.

If there is an obstruction or discontinuation in the beach section (bulkhead, large boulder, etc.), pace up to the obstruction, walk to the other side of it, and then continue your pace count on the other side. Do not include the width of the obstruction in your transect.

3. Count the animals of each sex separately. If a horseshoe crab is not buried, the two most common ways to determine its sex are its size and position. Males are for the most part smaller and clasped or crowded on top of females. The first pair of appendages for males is also bulbous (like a marble), so they have the strength to clasp a female tightly. The bulbous shape is diagnostic for males. 

There also tends to be more males than females.

4. To survey horseshoe crabs, you will start at one end of a marked section of beach.  At the “start time,” you should begin counting all horseshoe crabs (dead or alive, single males and females, swimming pairs, buried pairs, and clusters) along a 1,000 feet of beach. 

5. The Observer (first person) will walk along the "horseshoe crab line" and count out loud the number of horseshoe crabs and the Recorder (second person) records these observations on the Data Sheet. The Observer should always focus on counting horseshoe crabs that are spawning on the beach according to the following rules:

a.Crabs above the Surf Zone (on beach): Count all that are present.
b.Crabs in the Surf Zone: Count all that are present and include the submerged crabs that are obviously part of the spawning event.

6. Continue this way until you have sampled a 1,000 foot transect.

VERY IMPORTANT: You can stop while counting, but do not walk backwards and re-count!!!  

horseshoe-crab (1)_Fotor.jpg

Horseshoe Crabs Tracks in the Sand