Project Title: Population Assessment of Sea Turtles in Lake Worth Lagoon, Year 2
Project Manager: Paul Davis
Organization: Palm Beach County (Florida Government)
Grant Amount: $18,340.00
Completion Date: 2007-06-26
Summary: Lake Worth Lagoon (LWL) is a 20 mile long body of water located just west of the Atlantic Ocean along the coast of Palm Beach County, Florida. The lagoon was historically a freshwater lake, but it has been severely altered by human activities since the late 1800s. Today, the LWL is a moderately polluted estuarine waterway that receives ocean water from two man-made inlets. Palm Beach County has extensive monitoring of its high density nesting beaches, yet little is known about the sea turtles utilizing the LWL. The Lake Worth Lagoon Management Plan recommends evaluating sea turtle populations in the lagoon to provide information that will guide lagoon restoration management decisions. This information will also be useful in comparing this population with other inshore Florida populations. Five species of sea turtle have been reported in the lagoon, largely from stranding reports, incidental take from dredges, and anecdotal observations. Sighting data collected during aerial manatee surveys exists, but this information is ancillary and not species specific. This project will collect data primarily by netting which will be augmented by visual observations. The five main objectives of this project are: 1. Obtain baseline data on species abundance, size frequencies and sex ratios; 2. Determine Catch per Unit Effort (CPUE) at specific sites in the LWL; 3. Document the prevalence of fibropapillomatosis (FP), a potentially deadly disease that occurs at a high frequency among sea turtles in Indian River Lagoon and Florida Bay. 4. Obtain blood samples for genetic, sex ratio and disease analysis. 5. Determine habitat preference of sea turtles within the LWL by collecting GPS coordinates of sighting and captures and overlaying this with existing habitat data.
Results: Two sampling events were conducted by InWater Research Group, Inc during this reporting period. Sampling Event 8 was conducted on December 4 – 6, 2006. Seven visual transects were conducted covering 15.90 km of the Lake Worth Lagoon (LWL). A total of 46 green sea turtles were sighted on transect, generating a sighting rate of 0.25 green sea turtles/km. An additional six green sea turtles were spotted off transect, primarily during netting activities. Sampling Event 9 was conducted on April 2 – 4, 2007. Fourteen visual transects were conducted covering 43.91 km of the LWL. A total of 16 green, 2 loggerhead, and 1 unidentified sea turtles were sighted on transect, generating a sighting rate of 0.44 sea turtles/km. An additional 18 green sea turtles were spotted off transect, primarily during netting activities.
To date, 217 green, 5 loggerhead, and 1 unidentified sea turtles have been sighted during sampling events. The vast majority of sea turtle sightings have occurred in the northern portions of the LWL, especially in the vicinity of Little Munyon Island. This area contains some of the most robust seagrass beds in the LWL and apparently can support the foraging requirements of several green sea turtles.
During Sampling Event 8, tangle nets were set five times in the vicinity of Little Munyon Island and JD MacArthur Beach State Park, totaling 2.02 km net hours. One green sea turtle was captured during netting activities, generating a Catch Per Unit Effort (CPUE) of 0.49 turtles per km/net hour. Straight carapace length (SCL) for the turtle was 39.5 cm. The turtle was afflicted with FP and a blood sample was obtained. During Sampling Event 9, tangle nets were set four times in the vicinity of Little Munyon Island and JD MacArthur Beach State Park, totaling 0.89 km net hours. Seven green sea turtles were captured during netting activities, generating a CPUE of 7.89 turtles per km/net hour. Green sea turtle SCL ranged 32.3 cm – 61.7 cm. Two of the captured greens were afflicted with FP. Five dietary and seven blood samples were obtained.
Overall, 41 green sea turtles have been captured, 58% of which have been afflicted with FP. Additionally, four green sea turtles (13%) have required transfer to a rehabilitation facility due to healing boat injuries, monofilament entanglement, or severe FP. Green sea turtle SCL has ranged 29.8 cm – 61.7 cm, with a mean of 43.3 cm. One loggerhead sea turtle (72.0 cm) was captured in June 2005 and required transfer to a rehabilitation facility due to a healing boat injury.
Overall, FP has been observed in 23 of 40 (58%) captured green sea turtles. The percentage of green sea turtles afflicted with FP has ranged from 0% (March 2005) to 100% (June, September, and December 2006). Due to the small sample size, a true trend in seasonality cannot be drawn, though it appears FP frequency and severity may be more prevalent in the winter; additional sampling events are required to draw more complete conclusions.
As additional sea turtle data is collected in the LWL, ERM continually incorporates it into its permit comments and recommendations to the Lake Worth Lagoon Management Plan (currently under revision). (Author: Paul Davis)