Delaware Bay Horseshoe Crab Survey

Setup

• Arrive at the beach at least 30 minutes before high tide. Record the time you arrive in the space marked ARRIVAL AT SITE on the Beach Site Sheet. 

• Fill out the beach site sheet as completely as possible. Addresses and phone numbers of each survey team member are important in case we have questions about the data. Your address is also needed so we can send you a report of the survey findings for the season. Even if the weather prevents you from doing the survey, please fill out the Beach Site Sheet with all possible information and explain why the survey could not be completed. 

• To survey horseshoe crabs, you will start at one end of a section of beach, walk to the other end, and along the way place quadrats to count crabs. Flip a coin to decide which end of the beach section you will start: if heads, start at the down-bay end; and if tails start at the up-bay end. Circle down-bay or up-bay on the Beach Site Sheet where it says STARTING LOCATION. 

• Find the boundaries of the beach section by pacing from the beach access. The distance to pace depends on the beach you will be surveying. For example, if the beach access is at the midpoint of the beach section and the beach section is 1 km long, then you would pace 500 m from the access to the starting location you chose by flipping a coin. The beach coordinators will provide any specific instructions for your particular beach. 

• 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. 

Placing the Quadrat

• You will be surveying in groups with at least two people. A survey protocol diagram which is printed on the back of the Beach Site Sheet illustrates the placement of quadrats described below. 

• The `horseshoe crab line' you will follow is not a straight line, and may be above or below the water line. 

• 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 pace count. 

1. The quadrats on the Tally Sheet are numbered 1-100.
   If the beach section is 1 km: Choose 2 random numbers from 0 to 19 (Use the random number sheet and instructions to select the random numbers) to locate the first and second quadrats within the first 20 m stretch. Then pace 20 m from each random starting point to place the third and fourth quadrats in the next consecutive 20 m stretch. Continue in this way until you have sampled 100 quadrats. (See survey protocol diagram on reverse of beach site sheet.)
   If the beach is shorter than 1 km: Divide the length of the beach by 50 to find the distance between every other quadrat. For example, if the beach is 400 m, 400/50 = 8. Within each 8 m stretch of beach you will place 2 quadrats. Choose 2 random numbers from 0 to 7 to locate the first and second quadrats within the first 8 m. Then pace 8 meters from each random starting point and place the third and fourth quadrats in the next consecutive 8 m stretch. Continue in this way until you have sampled 100 quadrat locations. (See survey protocol diagram on reverse of beach site sheet.)

2. When you arrive at the quadrat location, place the quadrat at the toe of your foot on the last step. Place one side of the quadrat even with the line of horseshoe crabs and the opposite side towards the bay. Once the quadrat is in place, follow the instructions below under Counting Horseshoe Crabs. 

3. Once you are each done counting and all information is recorded, pick up the quadrat, and pace to the next quadrat. Begin pacing from the toe of your last step. Note: If there are two observers, it may be easier to leapfrog, so that each observer starts at one of the random starting points and then paces to every other quadrat.

4. It is the observer's responsibility to make sure the recorder gets all tallies before pacing to the next quadrat. 

Counting Horseshoe Crabs

• Once the quadrat is in place, do not move it until you are done counting. 

• You will count all horseshoe crabs 'in the quadrat'. A horseshoe crab is considered 'in the quadrat' if more than half of its body is inside the quadrat. 

• When animals are numerous, you may have to lift some up to assure you've counted all of those underneath. Heavy work gloves will be useful for this. Try to minimize disturbance to the spawning horseshoe crabs. Spawning females will be partially buried in the sand while laying eggs. Do Not Lift Up A Partially Buried Horseshoe Crab. 

• 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 crowding on top of females. There also tends to be more males than females. 

• Report your count of each sex to the recorder who will record the information under TOTAL. Report zero (0) when there are no horseshoe crabs. Do not try to move the quadrat from the preselected quadrat location just to include one or more nearby animals. Empty quadrats are just as important as those with horseshoe crabs because they will help reflect changes in the population.