Grant: 11-013R
Project Title: Population Assessment of Sea Turtles in the Lake Worth Lagoon – Phase III
Project Manager: Paul Davis
Organization: Palm Beach County (Florida Government)
Grant Amount: $9,460.00
Completion Date: 2012-05-15

Summary: 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. Under Phases I and II, Inwater Research Group (IRG) has been conducting marine turtle population assessments in Lake Worth Lagoon on behalf of PBC ERM since 2005 by conducting 3 day sampling events every quarter. The objectives of this work have been and have confirmed that juvenile green sea turtles are present year-round, specific areas have particularly high abundance similar to Indian River Lagoon, provided baseline data on abundance, size class structure, sex ration, and extent of fibropapillomatosis (FP) of marine turtles in the lagoon. This work has confirmed that LWL provides important developmental habitat for green turtles. This project is Phase III and will focus a reduced level of effort on the areas and time of year where turtles are most abundant, and will include continued quantitative sampling by visual transect to examine long-term trends in turtle abundance, as well as capture and tagging efforts that will include an assessment of rates and severity of FP in captured turtles.

Results: Five days of field effort were conducted by InWater Research Group, Inc during the period of this grant report. Approximately 128 kilometers of transects were conducted in the southern lagoon near the Boynton Inlet and in the northern lagoon near Little Munyon Island. Sampling events were conducted on August 22 – 25, 2011. The remaining sampling events were postponed due to poor weather conditions associated with Hurricane Irene. Sampling events resumed on August 31 and September 6, 2011. Quantitative visual transects using the “H.U.N.T.” (haphazard, unmarked, nonlinear transect) method, the “rodeo” method and dip nets were used for observations and captures.

Approximately 68 kilometers of HUNT transects were conducted near Little Munyon Island on August 22, 23, 24 and September 6, 2011. A total of 203 juvenile green sea turtles were observed. Sixteen juvenile green sea turtles were captured by dip net and/or hand captured using the “rodeo” method. This included an individual that was first captured in the LWL on August 23, 2011 and recaptured again in the Lagoon on September 6, 2011. Another individual, captured on August 23, 2011, was observed with flipper tags KSC927 and KSC976. This individual was captured during a cold stun event on January 7, 2010 in Mosquito Lagoon in Brevard County and released in the ocean at Juno Beach on January 13, 2010.

A total of 203 juvenile green sea turtles were observed in the vicinity of Little Munyon Island generating an Abundance Level of 2.98 green sea turtle observations per kilometer. Dip net and hand captures using the “rodeo” methods were used to capture sixteen juvenile green sea turtles. As in other phases, all turtles were measured, weighed, photographed and tagged with flipper and PIT tags prior to release. Straight carapace length (SCL) for the turtles was between 26.8 cm and 48.4 cm with a mean average of 38.2cm. Seven of the 16 captured greens were afflicted with FP. Two of the turtles were reported with light tumor loads, 3 had moderate tumors and 2 had heavy tumor loads and required transfer to a rehabilitation facility due to the severity of FP. Blood and dietary samples were obtained from both turtles; analysis will be discussed in the final report.

Throughout the course of this project, over 712 kilometers of transects have been conducted in the LWL. Between 2005 to present, 17 sampling events have been completed yielding approximately 555 juvenile green and 5 loggerhead sea turtles observations. The vast majority of sea turtle sighting have occurred in the northern portions of the LWL, especially in the vicinity of Little Munyon Island. This study indicates that the robust seagrass beds near Little Munyon Island create a valuable developmental habitat for green sea turtles.

Approximately 60 kilometers of HUNT transects were conducted near the Boynton Inlet on August 22, 24 and 30, 2011. A total of 5 juvenile green sea turtles were observed generating an abundance level of 0.08 green turtle observations per kilometer. Due to limited sightings, turtles were not captured in the southern portion of the lagoon.

The project has been publicized through press releases, and ERM’s monthly and quarterly newsletters. ERM also hosted a technical series presentation which discussed the results of the project with stakeholders. Educational posters have been installed in boat ramps near the project sites. As additional sea turtle data is collected in the LWL, ERM continually incorporates it into its permit comments and recommendations that pertain to the management of the Lake Worth Lagoon Management Plan.