Browsing by Subject "Leatherback sea turtle (Dermochelys coriacea)"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Bycatch Mortality of Leatherback Turtles in Trinidad's Artisanal Gillnet Fishery
    (2006) Gass, Jordan
    Although listed globally as critically endangered, leatherback turtles maintain a strong nesting population in Trinidad. Trinidad supports an estimated population of 6,000 nesting females, which despite increased beach protection still face significant risk in the form of coastal gillnets. Incidental captures also impact fishers, who incur financial losses in reduced fishing time from net damage and associated repair costs. During the 2005 nesting season, my project used fisher participation in villages in the northeast region of Trinidad to attempt to measure bycatch levels. The methods used to quantify bycatch are described and results discussed. Challenges encountered during the project are also assessed to plan modifications of project methods to enhance fisher participation and confidence in results.
  • Thumbnail Image
    ItemOpen Access
    Mark-Recapture Estimation of the Leatherback Sea Turtle (Dermochelys coriacea) Nesting Population at Matura Beach, Trinidad
    (2004) Hodge, Christina E
    Many researchers believe that Caribbean leatherback sea turtle (Dermochelys coriacea) populations are increasing. Since Trinidad currently hosts the world’s third largest leatherback nesting assemblage, accurate population estimates are needed for this area. Nature Seekers, Inc., a community-based environmental management organization, has been monitoring leatherback nesting on Matura Beach since 1990 and began its tagging project in 1999. The tagging project’s main goal was to determine the number of turtles nesting each year, but saturation tagging has not been possible given the resources available. However, as a season progresses, untagged turtle encounters constitute a smaller percentage of the overall leatherback encounters. The steady increase in percent of previously tagged turtles encountered during the season indicates that a significant portion of the population is being tagged and makes within season mark-recapture population estimation possible. This project examines the rate of recapture of tagged turtles, trends in the timing of recapture events, and the requirements for mark-recapture estimates of leatherback nesting populations. The probability of encountering an individual leatherback varies based on the time of the season and the number of days since it was last encountered. To account for this variability, each season was divided into cohorts based on a nine day nesting cycle. Closed capture, time dependent population estimates were derived for each cohort using Program Capture. Data from the 2000, 2001, and 2003 nesting seasons yielded mark-recapture population estimates averaging 62 percent greater than the minimum number of turtles encountered. This is consistent with the 40 percent beach coverage estimate provided by Nature Seekers at the initiation of this analysis. The 20 to 24 day average time between encounters of individual leatherbacks also supports the theory that Nature Seekers observes slightly less than half of the nesting events on Matura Beach since leatherbacks are known to nest every nine to ten days. Developing models to estimate sea turtle populations in situations where saturation tagging is not possible is critical for determining the status of endangered leatherback sea turtles. Future efforts should be directed toward improving nesting beach coverage, developing more accurate tagging effort indices, examination of the degree of nesting beach population closure, and the development of leatherback encounter probability models.
  • Thumbnail Image
    ItemOpen Access
    SPATIAL AND TEMPORAL TRENDS IN SEA TURTLE STRANDINGS IN NORTH CAROLINA, 1980-2003
    (2004) Chan, Valerie Ann
    Natural and anthropogenic activities cause injured or dead sea turtles to wash ashore or strand along coastlines. In North Carolina, the NC Wildlife Resources Commission collects stranding information on sea turtles as part of the Sea Turtle Stranding and Salvage Network, which was formed in 1980. In this study, I characterized temporal and spatial trends in sea turtle strandings in North Carolina. I described temporal trends in sea turtle strandings by year, season, sex, cause of death (if known), and mean body size, overall and by species. I also looked at spatial trends in stranding locations to determine if they were uniformly or aggregately distributed, overall and seasonally, by dividing the shoreline into 10 km bins and creating histograms. Stranding numbers have increased over the past 23 years, but seem consistent since 1995 when effort is believed to have been standardized. Strandings generally increased from May through July as well as from November to December. For turtles whose sex was reliably classified by observers, all species except leatherbacks exhibited a heavy female bias; leatherbacks showed a male bias. Mean size of strandings per species appears roughly constant. With the exception of leatherbacks whose mean stranding size corresponded with adults, the mean size of all species corresponded with juvenile size classes. Spatially, strandings are not uniformly distributed, but appear clumped around several areas along the North Carolina coast including the east ends of Raleigh, Onslow, and Long Bays, and just north of Cape Hatteras. These strandings correspond seasonally with alongshore currents modeled by Hart et al. (submitted). I was unable to find any correlation between frequency of surveys and numbers of stranding reports normalized for shoreline distance, suggesting that the distribution of the stranding data are not biased by sampling effort.