Abstract
An understanding of population dynamics is needed to assess the viability of migra- tory species. Monitoring of marine turtles at foraging grounds may detect changes in population trends that would take decades to be seen at nesting beaches. Mixed Stock Analysis using molec- ular markers provides a tool for estimating the origin of turtles sampled at foraging grounds. Here, we analysed mitochondrial DNA sequences of 90 immature green turtles at 2 foraging grounds in northwestern Sabah, Malaysia. We used data from 30 Indo-Pacific green turtle rookeries as the baseline for tracing the origin of turtles at the 2 foraging grounds. The inferred origins of turtles at the 2 locations were not different and indicated that the majority originated from 3 major popula- tions in Southeast Asia, the Turtle Islands of Sarawak in northwestern Borneo (29%), the Turtle Islands Heritage Protected Area (TIHPA) (28%) and Peninsular Malaysia (25%). Previous analy- ses indicated a 1:4 female-biased sex ratio at the foraging grounds, and based on our results, this largely reflects the use of unshaded beach hatcheries at some of the source rookeries for decades, which resulted in mostly female hatchlings. This result is supported by differences in the origins of male and female turtles. The result suggests a greater proportion of males originating from Peninsular Malaysia and fewer males originating from Sarawak and possibly the TIHPA com- pared to females. We discuss the implications of hatchery practices that influence sex ratios of hatchlings and recommend future research to improve the management of marine turtles in the region.
Highlights
Green turtles Chelonia mydas are circumglobally distributed and they are the most abundant large herbivore in many shallow marine habitats, they are considered globally endangered (IUCN 2004)
The relocation of eggs in Malaysia resulted in as much as a 100% female hatchling production from both the Turtle Islands Heritage Protected Area (TIHPA) (Chan 1988, Tiwol & Cabanban 2000) and hatcheries in Peninsular Malaysia (Limpus 1993, Ibrahim 1994), and this practice probably persisted for several decades
Laparoscopic examinations similar to those performed by Miller & Limpus (2003) showed that this foraging aggregation had a highly female-biased sex ratio of 80% female, indicating a possible link with the biased sex ratios of hatchlings previously incubated at hatcheries in the region (e.g. Tiwol & Cabanban 2000) as well as natural sex bias observed at some beaches
Summary
Green turtles Chelonia mydas are circumglobally distributed and they are the most abundant large herbivore in many shallow marine habitats, they are considered globally endangered (IUCN 2004). Laparoscopic examinations similar to those performed by Miller & Limpus (2003) showed that this foraging aggregation had a highly female-biased sex ratio of 80% female, indicating a possible link with the biased sex ratios of hatchlings previously incubated at hatcheries in the region (e.g. Tiwol & Cabanban 2000) as well as natural sex bias observed at some beaches It is not known, what proportion of the turtles at these foraging grounds originated from the different populations within the region. This study uses MSA to determine the origins of foraging male and female juvenile green sea turtles to consider possible links with rookeries thought to have strongly female-biased offspring production in the recent past, including rookeries with a long tradition of relocating nests into unshaded hatcheries
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