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INSTRUCTION KIT:
SURVEYING HORSESHOE CRABS

Return to Horseshoe Crab Monitoring Web Site

CONTENTS:

  1. This sheet of instructions
  2. Date of census and High Tide Times Table
  3. A 20 meter string for estimating pace length
  4. Pacing trial form
  5. Tally sheets for recording data.
  6. Beach site sheet for recording volunteer and physical information (names of observers and recorders, amount of cloud cover, etc.)
The 1 square meter quadrat used for sampling will be provided by survey coordinators. (Benjie Swan (609) 465-6552 or Bill Hall (302) 645-4253)

PREPARATION FOR THE SURVEY:

Determine your pace  Follow these instructions before your first assigned time to survey and preferably on a beach since pace length is affected by the surface you are walking on. This should take 15-20 minutes to complete.

Note: Each person only has to determine their pace ONCE for the whole season.

  1. Lay the 20 meter string out straight on the ground. You will use this to fill out the Pacing Trial Form.
  2. Count the number of paces it takes you to walk the length of the string using your normal stride. Remember that a pace is two steps. Enter this number in the space next to TRIAL 1 on the Pacing Trial Form.
  3. Repeat this process twice more. Enter the second number next to TRIAL 2 and the third number next to TRIAL 3.
  4. These three numbers are A, B, and C on the Pacing Trial Form. Add A, B, and C, and divide this number by three to find D, your average number of paces per 20 meters.
  5. Divide D by 20 to find your average number of paces per meter (E on the form).
Note: The average number of paces per meter is probably different for each person, because it depends on your stride length. It is important you do this yourself and know these numbers before you arrive at the beach.

Clothing and accessories

  • Wear appropriate clothing for weather and wet conditions at the water's edge. Consider using sunscreen during the day and insect repellent when needed. If thunderstorms are present do not go onto beach.
  • Bring a headlamp or flashlight. Headlamps are the most useful because they free up both hands.
  • Bring a clipboard or hard surface to write on. Also, bring a couple of pencils and a means to sharpen the pencils.
  • Work gloves may be useful if there are high densities of horseshoe crabs on the beach. You will have to lift animals up to count those underneath.
  • Shoes are a necessity. We recommend water shoes, old sneakers, or boots. Do no go barefoot.
  • An accurate wristwatch is needed for recording arrival time,as well as time survey is begun and finished.

SURVEY PROTOCOL:

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 survey findings for the season. Even if the weather prevents you from doing the survey, please fill out the survey sheet with all possible information and explain why the survey could not be completed.
  • To survey the 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 horseshoe crabs. Flip a coin to decide which end of the beach section you will start: if heads, start at the down-bay end; 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-kilometer long, then you would pace 500 meters from the access to the starting location you chose by flipping a coin. The survey coordinators, Benjie Swan and Bill Hall, will provide 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 Quadrats

  • 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 the 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 the obstruction, walk to 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 1st and 2nd quadrats within the first 20 m stretch. Then pace 20 m from each random starting point to place the 3rd and 4th 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 section is shorter than 1 km: Divide the length of the beach section 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 1st and 2nd quadrats within the first 20 m stretch. Continue in this way until you have sampled 100 quadrats. (See survey protocol diagram on reverse of beach site sheet.)
    2. When you have arrived at the correct quadrat location, place the quadrat at the toe of your 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 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.
    4. If there are 2 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.
    5. It is the observer's responsibility to make sure the recorder gets all the tallies before pacing to the next quadrat.

Counting Horseshoe Crabs

  • Once the quadrat is in place try not to move it again 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 there are numerous animals, 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 on the Tally Sheet. If the recorder is working with another observer, keep the tally in your head until the recorder can record the quadrat counts for you. Don't pick up the quadrat and move to the next quadrat location until you know the recorder has recorded all information for your present quadrat.
  • Report zero (0) when there are no horseshoe crabs within the quadrat. 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.

Once you are done surveying

Record the time in the space marked END OF SURVEY on the Beach Site Sheet.
Send all of the following to the address below: (Note: PLEASE DO NOT SEND FAX! WE NEED THE ORIGINAL DATA SHEETS!)
Benjie Lynn Swan
Limuli Laboratories
7 Bay Avenue, Dias Creek
Cape May Court House, NJ 08210
Phone No. (609) 465-6552
Fax No. (609) 465-0313
U.S. Department of the Interior || U.S. Geological Survey
11649 Leetown Road, Kearneysville, WV 25430, USA
URL: http://www.lsc.usgs.gov
Maintainer: lsc_webmaster@usgs.gov
Last Modified: August 23, 2007 dwn
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