Biology and conservation of marine turtle nesting in the Dominican Republic

Resumen

The loss of biodiversity has become one of the most pressing issues, which has lead to a growing global concern about the status of the biological resources on which human life depends. In recent decades there has been a decrease in individual populations of many species. In the Caribbean, marine turtle’s nesting rookeries have been reduced considerably, mainly due to human exploitation. A number of rookeries in this region have been studied for several decades and their status is well documented; however, many other Caribbean rookeries remain poorly described. The Dominican Republic (DR) is an area where information on marine turtle nesting activity is scarce and outdated. Surveys in the 1970s and 1980s constituted the main reference on the status of marine turtles in the DR; although more recent reports indicate that these species are under continuous threats. The lack of comprehensive studies and recent information, coupled with the evident threatened status of marine turtles in the country demanded an updated assessment to help target effective conservation actions. The present PhD study aims to identify the main marine turtles nesting rookeries in DR, describing the current spatio-temporal patterns of nesting, and assessing the likely impact of the current threats to these nesting stocks, based on a period of 5 years (2006 - 2010) of systematic survey within a conservation project. For the first time in recent decades we have documented the presence of three marine turtle species (Dermochelys coriacea, Eretmochelys imbricata and Chelonia mydas) still nesting in the DR; although the third species was found nesting in very low numbers. Nesting is concentrated in the protected areas of JNP and Saona Island, with nesting outside these areas being relatively scarce. Comparison of these results with earlier reports indicates that a profound decline appears to have taken place in the last thirty years. Illegal take of eggs was identified as the main threat to marine turtles, particularly on the eastern beaches of JNP. The present study highlights the need for adequate protection and management of these areas for marine turtle conservation in the DR, since the country seemed to be an important marine turtle nesting area in the past. In order to face threats, particularly egg take, an official program of artificial incubation was established to protect turtle clutches at JNP and Saona Island. In the JNP, clutches of the western and eastern beaches of the park (called WB and EB respectively), were incubated in hermetic boxes stored in Park rangers’ huts located in both places. The present study included the assessment of efficiency of this conservation measure through the investigation of how artificial incubation might be influencing the hatching success of clutches and the resultant sex ratios. The results revealed that the incubation method significantly influenced hatching success of clutches. In situ clutches had greater hatching success than those artificially incubated in WB and in EB. On the other hand, the incubation method significantly influenced incubation duration. Clutches artificially incubated in EB had longer incubation duration than in situ clutches and clutches artificially incubated in WB. Clutch relocation is currently the only viable conservation option for clutches on EB due to intense egg take, but steps are needed to ensure that natural sex ratio is not distorted. However, on the WB of JNP, in situ clutch incubation seems possible through beach protection. Hawksbill nesting population of Saona Island also face egg take as a major threat. Hence, a similar official conservation program, including artificial incubation, was also carried out for hawksbill clutches at Saona. In a four-year period study, a total of 400 hawksbill nests were recorded in 5 sampling areas of nesting beaches at the south coast of Saona. No significant effects of artificial incubation in hatching success were detected between years or incubation type. Likewise, there was no significant difference in emergence success between years or incubation type compared to in situ incubation. On the other hand, in 21 of the 22 artificially incubated clutches mean temperature during the thermosensitive period was lower than the pivotal temperature derived from laboratory studies, suggesting a male bias in artificially incubated clutches. Current level of egg take is unsustainable for the long term preservation of this nesting population. The low percentages of female hatchling production inferred from clutch temperature data calls for urgent changes in the conservation strategy adopted in Saona. Studies of in situ hatching success leaded to determine the reproductive value of the western beaches of JNP for the leatherback turtle as well as allowing obtaining data on beach parameters potentially affecting clutch incubation. A total of 64 leatherback clutches spanning three nesting seasons (2007, 2008 and 2009) were studied. The results of this study show that clutches of leatherback turtles in the JNP western beaches presented unusually high hatching success (75.2%) for this species, compared to other rookeries in the Caribbean and elsewhere. This study is particularly relevant in relation to La Cueva beach; this sector hosts 20% of the total clutches laid at western beaches of the Park and demonstrated the highest hatching success levels. However, it is less protected because it is located in the buffer zone out of the Park limits and deserves more protection. Given the exceptional value of hatching success and the current and potential threats affecting leatherback nesting beaches, additional efforts in regulation and management of the protected area are needed. During the conservation project of marine turtles nesting in DR a total of 10 hawksbill females were satellite tagged and tracked after nesting. For the study of the habitat-use patterns nesting hawksbills of Saona Island remained in the adjacent waters to their nesting beaches using small home range areas during internesting intervals. Core activity areas occurred in shallow waters mainly within 200 m isobaths and associated with coral reefs at the eastern-most tip of the island. The home ranges overlapped, showing similar location and extension both across turtles and years. This study highlights the relevance of DR protected areas for the conservation of hawksbill‘s internesting and foraging habitats, showing the need of enforcing existing legislation for the protected areas in the country. The present study also corroborates that the waters off Nicaragua and Honduras are exceptionally important foraging areas for the species in the Caribbean, as well as showing the turtles’ vulnerability in these waters.