THE EFFECT OF ANTHROPOGENIC ACTIVITY ON SEA TURTLE NESTING AND HABITAT USAGE IN FLORIDA, USA
Linz, Raschelli Anna-Elizabeth
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Sea turtles have complex life histories that make them difficult to study. Using easily-accessible data, such as nesting and stranding occurrences, can help to efficiently elucidate driving factors in the population dynamics of these imperiled species. The overall goal of the present study was to assess the efficacy of sea turtle protective measures in Florida. To accomplish this goal, two analyses were conducted. The first analysis sought to describe the relationship between nesting numbers of three species of marine turtles, the loggerhead (Caretta caretta), green (Chelonia mydas), and leatherback (Dermochelys coriacea), common in Florida and various anthropogenic and environmental variables. The analysis examined whether these species nest preferentially on beaches with less anthropogenic disturbance, and was accomplished by formulating generalized linear mixed models (GLMM) to predict nesting numbers for each of the study species. The variables used to predict this response variable were (i) the presence of protective measures, (ii) the presence of access restrictions, (iii) human population of the nearest town, (iv) geographic region, (v) beach angle, (vi) average annual sea surface temperature (SST), (vii) median φ for sediment size, and (viii) presence of lighting ordinance. Beach was analyzed as a random effect in the GLMM. This study also attempted to determine whether sea-turtle strandings in Florida depend on anthropogenic and environmental covariates. This was accomplished by conducting a series of point-pattern intensity analyses on sea-turtle strandings and (i) annual average SST, (ii) gridded human population, and (iii) presence of lighting ordinances. Most notably, the models illustrated a negative relationship between loggerhead turtle nesting numbers and presence of protective measures, and a positive relationship between green sea-turtle nesting numbers and presence of lighting ordinances. It was also found that nesting numbers of both of these species had a negative relationship with population of the nearest town. The notable results of point-pattern intensity analyses identified increased stranding incidence in areas with higher human population and presence of county-wide lighting ordinances. Although lighting ordinances appear to be implemented in optimal locations, the negative relationship between loggerhead turtle nesting numbers and presence of protective measures suggests that protected beaches are in suboptimal locations to aid nesting females. Lack of nesting in highly populated areas suggest that the two more-coastal species exhibit an aversion to cues that signal areas of high human population, whereas increased stranding incidence associated with areas of high human population density suggests that increased anthropogenic activity does pose a threat to marine turtles. This study underscores the importance of post-establishment assessment of protective measures, as compromises with developers or industry can render these attempts at protecting wildlife ineffective. The negative assessment results of the present study may motivate change to better help target species, while confirmation that measures are effective can secure more support for future efforts.