ABOUT THE PROGRAM
Florida Horseshoe Crab Watch is a citizen science-based program created to achieve the following goals:
Tag crabs and perform spawning beach surveys to collect data for estimating population size of horseshoe crabs in Florida waters.
Establish population metrics such as size, sex ratio, breeding behavior, and mass of horseshoe crabs.
Determine environmental variables associated with spawning behavior.
Establish habitat requirements and critical spawning beaches for horseshoe crabs.
Educate the public, both volunteers and others, about horseshoe crabs with the goal of increasing public participation and investment.
Origin
Florida Horseshoe Crab Watch was developed through a collaboration between FWC-FWRI, University of Florida’s Institute of Food and Agricultural Science Nature Coast Biological Station (UF/IFAS), University of Florida’s Department of Biology (UFDB), and Florida Sea Grant (FSG). The program was modeled on a long-term sampling project conducted on Seahorse Key, an island within the Cedar Keys National Wildlife Refuge (Brockmann and Johnson 2011), on the Delaware Horseshoe Crab Survey (Smith et al. 2002), and on Project Limulus (Mattei et al. 2015).
Survey design
The Florida Horseshoe Crab Watch program consists of beach spawning surveys, measuring and tagging a sample of spawning horseshoe crabs, and re-sighting the previously tagged animals. To the extent possible, the protocol is designed to follow the procedures of the Delaware Bay surveys (Smith et al. 2002). But the biology of Florida horseshoe crabs differs from that of Delaware horseshoes, which required some changes to the survey protocol. Florida horseshoe crabs are seasonal and are found nesting from late February through May (varying from year to year) and again from late August through October (Rudloe 1980; Sasson et al. 2020), so we conduct surveys in both the spring and the fall (Delaware Bay has only one season, April–June). We know that Florida horseshoe crabs are strongly influenced by inundation (tides and wind surge), more animals are present when water levels are higher (Rudloe 1980; Barlow, Powers, and Kass 1988; Brockmann and Johnson 2011). Therefore, each round of sampling consists of beach-transect surveys on three dates at the time of the highest predicted high tides, which are consecutive days, on or around the new or full moon. (In Delaware Bay surveys, sampling was done on the day of the new or full moon, two days before and two days after). As did the Delaware Bay survey, we used only daytime high tides, as nighttime tides occur at too late an hour for volunteers. The surveys begin at the time of the predicted high tide, and four rounds of surveys (two new moon and two full moon) are conducted each season. We chose not to sample using the quadrat method used in Delaware Bay, because horseshoe crab populations in Florida are much sparser than those in Delaware, so all crabs in a designated area can be counted (Smith and Bennet 2004). Also, Florida horseshoe crabs are often patchily distributed, which violates assumptions of random encounters on which quadrat sampling is based.
Site selection
Survey locations are established after a season of scouting surveys to ensure that they represented viable spawning beaches. When possible, beaches deemed hot spots, based on high abundance of horseshoe crabs in the public-report data, are selected for Florida Horseshoe Crab Watch surveys, but some are not used because they are not sufficiently accessible for volunteers. The survey distance for each beach transect is determined by beach size and physical landmarks or blockages.
Survey protocol
For each survey, volunteers begin walking the shoreline at the time of the predicted maximum high tide. Volunteers work in pairs recording the number of horseshoe crabs observed nesting on the beach or just offshore or swimming near the beach (because of water turbidity, this is not more than 1 m offshore). A note was made distinguishing between paired horseshoe crabs (male attached to a female), unpaired males, unpaired males in physical contact with pairs (i.e., satellites) and unpaired females, and of the numbers of each (Brockmann 2003). After walking the survey area, volunteers pick up at random horseshoe crabs to be tagged and gently place them into buckets, where they are held until the spawning survey is complete. If any previously tagged horseshoe crabs are observed, the tag number and status of the horseshoe crab (alive or dead) is recorded. If dead, the tag is removed, the number recorded, and the tag discarded. If the horseshoe crab is alive, its tag number is recorded, and the animal is returned to the water at the shoreline. Any data collected from previously tagged horseshoe crabs during the surveys are submitted to the USFWS by the Florida Horseshoe Crab Watch statewide coordinator. These data are used as part of a range-wide program to establish horseshoe crab population size and movements. Tags include a website link so that members of the public who find a tagged crab can report it directly to the USFWS (ASMFC 2020). Once the volunteers reached the end of the beach transect, the horseshoe crabs that are captured are measured and tagged. Each individual is examined for its condition, which is used as an estimate of age (young, medium, old; Shuster 2009), and whether it is missing any limbs. Individuals are then sexed, the prosoma width (mm) measured, and the crab weighed (g) using a spring scale or digital scale (Shuster 2009). Finally, a tag with a unique number, provided by the USFWS, is inserted into the prosoma on the left side. This is done by creating a small hole in the shell using a sharpened awl and inserting the tag into the hole. The tag is ribbed so it cannot fall out after it is pressed into the shell (Figure 1; Beekey and Mattei 2008). For each survey, data about volunteers’ efforts are also recorded on the data sheet, including the number of miles traveled, the number of hours donated, and the number of interactions with the public. Interactions with the public included encounters with anyone in the area who asked the volunteers what they are doing; these events constitute part of the program’s outreach.
Coordination structure and training
The Florida Horseshoe Crab Watch program is maintained by one statewide coordinator who oversees site coordinators. Site coordinators are normally education coordinators at science-based organizations such as UF/IFAS, the Florida Department of Environmental Protection and environmental nonprofits such as the Marine Discovery Center in New Smyrna Beach. Some site coordinators are not affiliated with an organization. Site coordinators are trained individually or in small groups. This training includes the basic volunteer training (described below) and coordinator specific training. The site coordinator manages the survey locations, local survey schedule, and recruitment of volunteers. Once a site coordinator is trained, a volunteer training event is held. These training events are designed to be systematic and thorough. They began with an overview of horseshoe crab biology, life history and anatomy, and management and an introduction to citizen science. Volunteers were encouraged to ask questions throughout the presentation as a means encouraging their interest and engagement. After the presentation, a series of YouTube videos, developed by FWRI, UF/IFAS, and FSG, are shown to introduce and demonstrate the survey process. The YouTube (Florida Horseshoe Crab Watch) training videos are available to view at any time by volunteers, coordinators, and the general public. Finally, the volunteers cycle through five stations designed to mimic survey data collection. Each volunteer practices determining the sex and age of horseshoe crabs, measuring, weighing, and tagging crabs, and recording data. If the training is held near the first survey date of the season, volunteers join the coordinator for an on-site practice survey. This allows for further hands-on experience and the opportunity for volunteers to ask questions before surveys. If an on-site practice survey is not possible before the first survey of the season, a mock beach transect is created to demonstrate a typical survey. Once volunteers have attended the training event, they are eligible to sign up to formally participate in Florida Horseshoe Crab Watch surveys.
Data Analysis and Results
Data collected are used to establish horseshoe crab population size within Florida. These data take an average of 10 years to establish. But preliminary data have been used to inform management decisions on both a county, state, and national level. All data is publicly available by request. The program has spurred multiple new discoveries relating to horseshoe crabs, including never before observed epibiont relationships, and spawning behavior tied to wind action, rather than tidal action. An overview of methods, and data accuracy of the Florida Horseshoe Crab Watch Program, and the Horseshoe Crab Spawning Public Reports are currently in the process of publication in Citizen Science: Theory and Practice. The methods above are an excerpt for this publication. Additionally, the program has facilitated a greater sense of community engagement, and natural resource appreciation.
Florida Horseshoe Crab Watch Biological and Morphological Trends
Horeshoe Crabs are sexually dimorphic female horseshoe crabs are larger and weight more than males. The Florida Horseshoe Crab Watch Program collects sex, age, width, and weight data from all crabs tagged. With this data we see general trends in size and weight of the crabs. We also can observer sex ratios and age trends. The following data represents the programs's findings. The weight and prosoma width data has been cleaned, removing NAs and outliers (greater or less than 3 standard deviations of the mean). All NAs in the sex and age data were excluded from analysis.
Statewide, the average female horseshoe crab weights 1279.3 grams and has a prosoma width of 208 mm. Male horseshoe crabs on average weight 433.9 grams and have a prosoma width of 153.9 mm.
The sex ratio varies by county, but on a state wide scale there is a ratio of 1.4 male horseshoe crabs for every 1 female horseshoe crab.
Finally, the general age makeup of horseshoe crabs that have reached sexual maturity is, 35% young crabs, 45% medium aged cabs, and 20% old aged crabs. Horseshoe crabs can live for well over 10 years after they reach maturity, so young crabs are at least 9 years of age, and crabs with worn shells are likely to be over 15 years old.
Yearly Florida Horseshoe Crab Watch Statistics
Data gathered during the January 1st, 2018 to December 31st, 2018 period consisted of 393 unique sampling events across 24 sites. With a total of 5998 counted, 1393 crabs tagged, and 73 crabs resighted.
The county with the largest number of crabs observed during the spring season was Franklin County with 1176 counted. During the fall Levy County saw the largest number of crabs with 1461 counted.
The county with the highest number of crabs per meter was Nassau County with 5.046 crabs per meter surveyed. During the fall Nassau County saw the largest number of crabs per meter with 0.32 crabs per meter surveyed.
The county with the most surveys during the spring season was Volusia County with 93 surveys. During the fall Levy County had the most surveys with 55 surveys.
The county with the most tagged crabs during the spring season was Levy County with 356 tagged crabs. During the fall Levy County saw the largest number of crabs tagged with 394 tagged.
The county with the most resighted crabs during the spring season was Levy County with 8 resighted crabs. During the fall Levy County saw the largest number of crabs resighted with 44 resights.
Yearly Florida Horseshoe Crab Watch Volunteer and Outreach Statistics
Florida Horseshoe Crab Watch also records hours spent, miles driven, and educational contacts made while volunteering for the program. The following statistics showcase the incredible amount of time and effort made by volunteers during the January 1st, 2018 to December 31st, 2018 period. These data were collected by 202 volunteers who donated a total of 2658 hours and drove a total of 45714 miles and educated a total of 1075 members of the public while surveying.
The county with the most unique volunteers during the spring season was Levy County with 55 volunteers. During the fall Levy County saw the largest number of unique volunteers with 45 volunteers.
The county with the volunteers who donated the most time during the spring season was Volusia County with 591.9 hours. During the fall Levy County saw the largest number of hours donated with 392.25 hours.
The county with volunteers who drove the most miles during the spring season was Levy County with 8250.5 miles. During the fall Levy County had the largest number of miles driven with 9101.5 miles.
The county with the most educational contacts in the the spring season was Volusia County with 243 educational contacts made. During the fall Levy County saw the largest number of educational contacts made with 122 contacts.
Summarized tables can be found below. Raw data is avalible upon request, please reach out to FHCWCoordinator@myfwc.com
| County | Sex | Weight | PW |
|---|---|---|---|
| Brevard | F | 896.5 | 184.6 |
| Brevard | M | 407.3 | 145.1 |
| Charlotte | F | 310.0 | 136.0 |
| Dixie | F | 1322.1 | 210.9 |
| Dixie | M | 424.6 | 152.7 |
| Franklin | F | 1647.1 | 227.0 |
| Franklin | M | 550.3 | 168.6 |
| Hernando | F | 995.1 | 190.9 |
| Hernando | M | 344.0 | 141.0 |
| Hillsborough | F | 871.0 | 182.8 |
| Hillsborough | M | 308.6 | 137.0 |
| Indian River | F | 994.4 | 195.9 |
| Indian River | M | 371.0 | 143.8 |
| Lee | F | 1180.0 | 193.7 |
| Lee | M | 357.0 | 140.4 |
| Levy | F | 1388.0 | 215.4 |
| Levy | M | 436.7 | 157.4 |
| Manatee | F | 914.0 | 190.1 |
| Manatee | M | 357.3 | 142.6 |
| Monroe | F | 1247.1 | 209.4 |
| Monroe | M | 432.4 | 154.4 |
| Nassau | F | 2329.8 | 268.4 |
| Nassau | M | 884.6 | 200.2 |
| Pasco | F | 854.7 | 182.3 |
| Pasco | M | 306.3 | 136.2 |
| Pinellas | F | 1069.7 | 195.8 |
| Pinellas | M | 367.5 | 144.3 |
| Sarasota | F | 993.3 | 190.0 |
| Sarasota | M | 323.6 | 137.7 |
| Taylor | F | 1304.7 | 206.0 |
| Taylor | M | 466.5 | 154.6 |
| Volusia | F | 872.0 | 196.5 |
| Volusia | M | 402.7 | 149.3 |
| County | ratio |
|---|---|
| Brevard | 1.51 |
| Dixie | 1.57 |
| Franklin | 1.13 |
| Hernando | 1.33 |
| Hillsborough | 1.40 |
| Indian River | 0.62 |
| Lee | 2.33 |
| Levy | 1.39 |
| Manatee | 1.23 |
| Monroe | 1.12 |
| Nassau | 1.86 |
| Pasco | 2.93 |
| Pinellas | 1.78 |
| Sarasota | 6.00 |
| Taylor | 1.61 |
| Volusia | 0.84 |
| Year | Season | County | Surveys | TotalCrab | Tag | Resight | CrabsperMeter | EduContacts |
|---|---|---|---|---|---|---|---|---|
| 2018 | Spring | Dixie | 5 | 40 | 21 | 0 | 0.010 | 16 |
| 2018 | Spring | Franklin | 23 | 1176 | 132 | 5 | 0.128 | 78 |
| 2018 | Spring | Hillsborough | 9 | 18 | 0 | 0 | 0.003 | 1 |
| 2018 | Spring | Levy | 55 | 752 | 356 | 8 | 0.063 | 201 |
| 2018 | Spring | Nassau | 39 | 156 | 87 | 1 | 5.046 | 168 |
| 2018 | Spring | Pinellas | 18 | 104 | 0 | 0 | 0.007 | 27 |
| 2018 | Spring | Taylor | 6 | 2 | 2 | 0 | 0.001 | 10 |
| 2018 | Spring | Volusia | 93 | 234 | 145 | 1 | 0.003 | 243 |
| 2018 | Fall | Dixie | 8 | 77 | 41 | 2 | 0.013 | 28 |
| 2018 | Fall | Franklin | 18 | 146 | 54 | 4 | 0.020 | 48 |
| 2018 | Fall | Hernando | 9 | 155 | 71 | 2 | 0.033 | 67 |
| 2018 | Fall | Hillsborough | 7 | 18 | 0 | 0 | 0.003 | 0 |
| 2018 | Fall | Levy | 55 | 1461 | 394 | 44 | 0.150 | 122 |
| 2018 | Fall | Manatee | 1 | 0 | 0 | 0 | 0.000 | 0 |
| 2018 | Fall | Nassau | 30 | 8 | 7 | 1 | 0.320 | 42 |
| 2018 | Fall | Pinellas | 8 | 641 | 4 | 1 | 0.103 | 0 |
| 2018 | Fall | Taylor | 9 | 1010 | 79 | 4 | 0.257 | 24 |
| Year | Season | County | UniqueVol | TotalHours | Mile |
|---|---|---|---|---|---|
| 2018 | Spring | Dixie | 5 | 47.00 | 1200.0 |
| 2018 | Spring | Franklin | 24 | 227.50 | 5933.0 |
| 2018 | Spring | Hillsborough | 1 | 0.00 | 0.0 |
| 2018 | Spring | Levy | 55 | 400.75 | 8250.5 |
| 2018 | Spring | Nassau | 13 | 334.70 | 3978.4 |
| 2018 | Spring | Pinellas | 3 | 0.00 | 0.0 |
| 2018 | Spring | Taylor | 8 | 24.50 | 1228.0 |
| 2018 | Spring | Volusia | 23 | 591.90 | 3233.0 |
| 2018 | Fall | Dixie | 10 | 64.50 | 1410.0 |
| 2018 | Fall | Franklin | 26 | 283.00 | 6715.0 |
| 2018 | Fall | Hernando | 7 | 33.50 | 239.0 |
| 2018 | Fall | Hillsborough | 1 | 0.00 | 0.0 |
| 2018 | Fall | Levy | 45 | 392.25 | 9101.5 |
| 2018 | Fall | Manatee | 1 | 2.50 | 11.0 |
| 2018 | Fall | Nassau | 14 | 176.80 | 2474.0 |
| 2018 | Fall | Pinellas | 11 | 0.00 | 0.0 |
| 2018 | Fall | Taylor | 17 | 80.00 | 1941.0 |
