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Sea turtle nesting trends for Florida, USA, come from the state's Index Nesting Beach Survey (INBS) Program as presented by Blair Witherington, Florida Fish and Wildlife Conservation Commission, Florida Marine Research Institute. Within the INBS program, 316 km of nesting beach divided into zones averaging 0.8 km in length have been monitored daily during a 109-day season each year starting in 1989. Additional beaches added since the program began bring the total length of Florida index beaches to 396 km. On index beaches, nests and nesting attempts (from track evidence) are recorded by species, location, and day using a standardized system of survey techniques, training, and data reporting. State nesting trends are not uniform for the entire state.
Daily surveys of sea turtle crawls (track evidence from nesting attempts) on nesting beaches are one of the most widely used indicators of sea turtle abundance. In Florida, USA, this evidence of sea turtle nesting activity is recorded within the Index Nesting Beach Survey (INBS) program. The consistent, standardized methods of the INBS program allow an accurate examination of sea turtle nesting trends that is not biased by changes in monitoring effort. The purpose of this presentation is to outline temporal and spatial trends in the nesting of three species using Florida beaches, loggerheads (Caretta caretta), green turtles (Chelonia mydas), and leatherbacks (Dermochelys coriacea).
The Index Nesting Beach Survey program comprises thirty two beach sites that represented the principal sea turtle nesting areas of Florida. Each beach is divided into zones approximately 0.8 km in length. The season that INBS surveys take place also is representative and is standardized among beaches to begin 15 May and end 31 August each year. Index Nesting Beach Surveys represent approximately 67%, 74%, and 34% of loggerhead, green turtle, and leatherback nests, respectively. To examine temporal nesting trends, researchers used a core set of index beaches totaling 316 km in length where surveys were conducted. To examine spatial nesting trends, we used data from all INBS beaches, totaling 396 km, for the most recent two years.
Florida index beaches are monitored each nesting season by a network of trained surveyors who follow a standardized protocol for crawl identification, survey methods, and data reporting. Surveyors conduct daily appraisals of tracks that have resulted from nightly nesting attempts by female turtles. Characteristics of tracks are used to assess the species of the turtle that made the track and whether the track resulted in a nest or an abandoned nesting attempt. Crawl assessment skills are reinforced at annual pre-season workshops, which all Index beach-surveyors are required to attend. The accuracy of morning track surveys is tested during the season by observing nesting turtles at night on a sample of beach sites and by comparing these verified nest/species identifications to the crawl observations made by surveyors the following morning. Preliminary results show that the error rate in nest identification is 7.5% for loggerhead tracks (n = 451) and 12% for green turtle tracks (n = 41), and that error in species identification is 1.5% (n = 139).
The spatial distribution of loggerhead and green turtle nesting was similar, each having peaks in nesting on the Atlantic coast at latitude 280 N. Leatherback nesting was largely restricted to the Atlantic coast between latitudes 270 and 280 N.
For the period 1989-2002, the annual number of loggerhead nests at the core set of index beaches ranged 39,091 to 59,918; green turtle nests ranged 267 to 6981; and leatherback nests ranged 27 to 357. Nesting in Florida by green turtles and leatherbacks has increased during the period of 1989-2002, but loggerhead nesting has shown a series of nesting ups and downs revealing no discernable trend for the 14-year period (Loggerhead - INBS, Green - State, Leatherback - INBS). Nesting numbers for green turtles showed a clear biennial periodicity, with odd years having low nesting and even years having high nesting. To reduce variation for linear regression, we grouped green turtle nesting into two-year (high-nesting/low-nesting) blocks (Green - INBS).
To examine spatial trends, researchers combined INBS zones into 10 beach groups and plotted nesting trends for each group (Loggerhead-Beaches, Green-Beaches). Correlation coefficients describing twelve-year slopes at each surveyed beach show considerable variation in temporal trends among beaches for both loggerhead and green turtle nesting.
However, these increases are not observed in every region of the state. Although significant nesting increases for loggerheads were seen in the southwest and central east-coast, regions of Florida, southeast Florida did not show this trend. Green turtle nesting seemed to have increased significantly at beaches where there were sufficient data, with the most prominent increases on southeast and central east-coast beaches. Leatherbacks were too few to divide this way among beach groups. Many of the beaches where nesting increases are seen can be characterized as having relatively sparse human habitation (undeveloped beach as in State, county parks, and wildlife refuges, or low-density single-family, non-commercial development) and relatively little artificial lighting visible from the beach.
The sea turtle nesting trends we portray are a retrospective look at previous years and cannot forecast future nesting. These trends describe only the segment of each turtle population that comprises adult females visiting nesting beaches. Because these trends are an index of the oldest members of the population, they lag decades behind events that affect their numbers.
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