The diamondback terrapin (Malaclemys terrapin) is the only resident brackish water turtle in the United States. Ranging from Massachusetts to Texas. This estuarine turtle spends much of its time in coastal wetlands such as marshes and mangroves but have been found in seagrasses. They feed primarily on bivalves, have strong site fidelity, and live to be 20-25 years in the wild. Studies on their basic biology and ecology have been published throughout their range with the exception of the Florida panhandle.
In 2005 the Marine Science Academy at Washington High School (MSA) was asked to survey coastal estuaries within the Florida panhandle to determine whether diamondback terrapins (Malaclemys terrapin) existed there.
Methods – Presence/Absence
To determine presence/absence MSA identified boat ramps near suitable terrapin habitat. “Wanted” signs were placed at these ramps with our contact information and beach walk surveys were conducted seeking terrapins or terrapin sign. Since the best time to conduct beach surveys is May and June (not suitable for high school), that part of the project moved to program director and his family.
Surveys were conducted and terrapins were found in each of the six counties between the Alabama state line and the Apalachicola River.
Methods – Relative Abundance
The next question was to assess their relative abundance. To do this the team followed a protocol used by Tom Mann with the Mississippi Department of Natural Resources we call the “Mann-Method”. There are recognized assumptions with this method.
- Every sexually mature female within the population nests each season.
- Each female will lay more than one clutch per season but never more than one in a 16-day period.
- You know where all nesting beaches are located.
- The sex ratio to males is 1:1.
Going on these assumptions, every track, nest, or depredated nest on the nesting beach within a 16-day window is equivalent to one female. If the sex ratio is 1:1, then each female is equivalent to one male, and you have a relative abundance of the population. That said, there are publications suggesting the female: male ratio could be 1:3 or even 1:5 in the Florida panhandle. We would report the relative abundance as 1:1 – 1:5 for each nesting site.
Another method of estimating relative abundance is conducting a 30-minute head count. From a fixed location, or drifting in a kayak across the lagoon, every head spotted in a 30-minute period is logged. The assumption here is that if the average number of heads / 30-minutes increase or decreases over time, the relative abundance within the population is increasing or decreasing as well.
Trained volunteers conducted these surveys at least once a week at each nesting beach from April 1 to June 30 each year.
2022 Data Update
- 47 volunteers were trained in March of 2022; 21 (45%) participated in surveys.
- 173 surveys were conducted; 346 hours were logged.
- Terrapins (or terrapin sign) were encountered during 43 of the surveys – Frequency of Encounters = 25% of the surveys.
- Surveys occurred in Escambia, Santa Rosa, Okaloosa, and Bay counties. Encounters occurred in all counties except Bay.
Beach Surveys – 2022
|County||# of Surveys||# of Encounters||Frequency of Encounters|
Head Count Surveys – 2022
|County||# of Surveys||Range of Heads/30-min||Mean of Heads/30 min|
Estimated Relative Abundance Using the Mann-Method
|County||Nesting Beach Surveyed||Ratio 1:1||Ratio 1:3||Ratio 1:5||Relative Abundance for the County|
|Santa Rosa||1||12||24||36||2-48 terrapins|
Terrapins Captured – tagged – and tissue samples collected
|County||# of Terrapins Captured/Tagged/Tissue Collected|
At the beginning of this project Objective 1 was to determine whether diamondback terrapins existed in the Florida panhandle. That objective has been met – they do, we have at least one verified record in all six counties between the Alabama state line and the Apalachicola River.
Objective 2 is to determine the relative abundance within these counties. The first step in addressing this objective is to determine where terrapins are nesting in each. Nesting beaches have been identified in Escambia, Santa Rosa, and Okaloosa counties – but we are not sure whether ALL of the nesting beaches in those counties have been identified.
Known nesting beaches in Escambia County have changed over time. Two of the three nesting locations have become inactive in recent years and other potential beaches have not been adequately surveyed to determine whether they are being used or not. Based on one active nesting beach, the relative abundance of terrapins in Escambia County is low. Estimations using the Mann-Method suggest that there are between 2-24 terrapins present.
There are numerous potential nesting locations in Santa Rosa County but only a few have been adequately surveyed. Currently there two active nesting beaches being surveyed and the relative abundance at these has run between 30-80 animals at one location, 6-36 at the other. Going with this, there are between 6-80 terrapins present.
Okaloosa has only recently been surveyed. There are currently three active nesting beaches being surveyed and most of the nesting is occurring at one of those. The location of these beaches suggests that these are all animals of the same group or clad and part of the same population. Based on the results there are between 2-72 terrapins present.
Surveys are JUST getting underway in Bay County and no surveys have been conducted in Walton.
These data suggest that the relative abundance in each county is less than 100 and small when compared to other locations within their range.
The results are only as good as the data being used. The volunteers participating in this project are doing an excellent job, but the frequency of nesting beach visits and head counts surveys are lower than needed to make accurate assessments. Several of the nesting beaches are in difficult places for volunteers to reach frequently and thus not surveyed as frequently as we would need. More volunteer participation could help this. Keep in mind that the Mann-Method also focuses on nesting females and males, immature females are not accounted for so the population would be slightly larger than estimated using this method. That said, we do believe that the populations in this part of their range are most likely smaller than other parts of their range. These surveys will continue.
Questions or comments can be directed to Rick O’Connor, Florida Sea Grant, University of Florida IFAS Extension, firstname.lastname@example.org.
Source: UF/IFAS Pest Alert
Note: All images and contents are the property of UF/IFAS.