Boat strike assessment on resident sea turtle in Mabul Island, Sabah, Malaysia

• Main Author: Phu, Jiun Lang
• Format: Thesis
• Language: English; English
• Published: 2020
• Subjects: QL640-669.3 Reptiles and amphibians
• Online Access: https://eprints.ums.edu.my/id/eprint/40962/1/24%20PAGES.pdf; https://eprints.ums.edu.my/id/eprint/40962/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/40962/

Boat strike is one of the major threats to sea turtles especially at shallow reef areas where boat traffic is heavy. In the Southeast Asian region, there is no published study on boat strike on sea turtles. The current study aims to determine the effects of boat strikes on the reside;nt sea turtles in Mabul Island ( 4.246° N 118.630° E), which is one of the tourist hotspots and is also key foraging ground of green ( Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles, located in southeast Sabah, Malaysia. Wild green and hawJ<sbill turtles in Mabul were hand-captured in the reefs and were brought onto the boat for data collection. A detailed physical examination was done on all captured turtles before they were released back to the water. The data consisted of 432 individual sea turtles caught from March 2013 to November 2017 (43 days of field work), with 405 (93.7%) greens and 27 (6.3%) hawksbills. There were 38 (9.4%) green turtles and no hawksbill turtle found to have boat strike injuries. A total of 58 boat strike injuries were documented, which consisted of cut wounds (58.6%), parallel cuts (19.0%), deep incised wounds (13.8%), and blunt force wounds (8.6%), with cut wound being the dominant type (X2 = 36.207, df = 3, p < 0.01). This study developed a novel approach to categorise the severity of these injuries using the ranking system, with increasing order of severity from Ranks 1 to 6. The number of different boat strike injury severity rankings were evenly distributed (x2 = 3.508, df = 4, p = 0.48). The severity of the boat strike injuries on sea turtles is dependent on the boat speed and the ability of the turtles to avoid the approaching boats. The current study showed that the posterior part of the carapace of a sea turtle is most susceptible to boat strikes compared to other parts of the body. The established dive sites located in close proximity to the island (between 200 and 350 m from Mabul) were found with highest percentages of turtles with boat strike injuries: Paradise 1 (15.4%), Paradise 2 (11.1), Panglima Reef (10.9), and Lobster Wall (9.5%), as opposed to those further away (between 1,000 and 1,500 m from Mabul): Ray Point (4.7%) and Eel Garden (4.3%). Higher percentage of sea turtles with boat strike injuries found at Paradise 1, Paradise 2, and Panglima Reef may be caused by the higher localised boat traffic (between 5 and 20 passing boats every minute at daytime) surrounding the island as motorised boats are the main mode of transportation in Mabul. It is suggested that boat speed regulations should be implemented at these areas and reef areas with depth < 20 m as foraging turtles will swim to the surface to breathe. This study has provided important baseline information on the effects of boat strike incidents on green turtles and this issue needs to be addressed as Mabul is one of the key foraging grounds for green and hawksbill turtles coming from various natal origins.