New Information and Recommendations on Sea Turtle Ecology in the BHS
Excerpted from Ecosystem Based Management in the Bird’s Head Seascape, Conservation International, et.al.
The Bird’s Head Seascape is a refuge to four of the world’s seven sea turtle species, and holds globally important nesting beaches and foraging grounds. These threatened species travel through the coastal waters of the BHS on their long migratory journeys to the Pacific and Indian Oceans. Throughout their lifecycle, sea turtles play an important role in the ecology and well-being of coastal and open ocean environments. Scientists believe that Hawksbill turtles may maintain the health of coral reef systems by grazing on sponges and coralimorphs, which if left to grow unchecked, overgrow corals and kill the reef. Because of these relationships, researchers believe that declining numbers of Hawksbill turtles may be a factor in the inability of reefs to resist increasing pressures from pollution, algal overgrowth, overfishing, and climate change. Constant grazing by Green sea turtles increases the health and growth rate of seagrasses. As the top predators of jellyfish, Leatherback sea turtles are thought to inadvertently protect larval fish from predation. Sea turtles are also culturally important to people throughout the tropical Pacific, playing an important ceremonial role. Even though sea turtles are protected by law in Indonesia, they are threatened by people and predators who remove eggs from nests, fishers who hunt adults, and fishing nets that entangle and drown individuals at sea. Sea level rise and coastal development put them at further risk by reducing the size and condition of nesting and foraging habitats worldwide. Information on the location of important turtle nesting beaches, feeding grounds, and migratory pathways is critical to managing these iconic species, especially if migrations include passage through areas where they may be killed. Between 2005 and 2009, local community groups in Raja Ampat, Abun and Cendrawasih Bay were trained to monitor Leatherback and Green turtle populations. WWF-Indonesia scientists and partners used satellite tags to document the migration patterns and distribution of 5 Olive Ridley and 11 Green turtles over a one to two year period. Inputs reflect results from these and other sea turtle studies in the region.
Sea turtles in the BHS are threatened by:
- Illegal poaching of eggs, and hunting of adults for meat and carapace;
- Destruction of turtle nests and egg predation by monitor lizards, dogs, and pigs;
- Loss of nesting habitat due to coastal development (seawalls, beach modification, and erosion from vegetation removal), sea-level rise, and storms;
- Loss of seagrass beds used as Green turtle foraging grounds through the smothering with mud and sand from coastal development, land reclamation and road construction, and trampling during gleaning;
- Entanglement and drowning as bycatch in long lines and trawls, or in discarded fishing nets, especially gill nets, beach seine, and pound nets, especially during nesting season;
- Changes in sex ratios of hatchlings caused by increased temperatures of beaches affected by sedimentation from mining run-off, forest clearance around watershed areas, and loss of coastal vegetation such as mangroves, Pandanus, and other beach trees;
- Baiting for the shark finning fishery attracts sharks to hatchling areas, leading to high rates of hatchling predation;
- Plastic ingestion leading to death by gut blockage and starvation.
KEY FINDINGS AND INPUTS
- Individual Green, Hawksbill, and Leatherback sea turtles returned to the same nesting areas about every three to four years;
- Nesting beaches with the highest number of nests have wide and high sandy stretches, suitable sand/substrate structure, beach vegetation (especially trees), and no beach lights.
- The following beaches in the BHS were discovered to be regionally and in some cases globally important nesting beaches:
• Green turtles: Ayau-Asia, Piai-Sayang, Waigeo, Venu-Kaimana, Pisang-Tuturuga-FakFak, Wairundi
• Hawksbill turtles: Misool, Wayag-Sayang, Venu-Kaimana
• Leatherback sea turtles: Abun-Jamursba Medi, Warmon, Kaironi
• Olive Ridley sea turtles: Abun-Jamursba Medi, Warmon, Kaironi
- After remaining in an area for a few months to nest, individuals of all species dispersed to areas outside the BHS, including to the Arafura Sea, South Kalimantan, throughout Southeast Asia, Eastern Australia, New Zealand, and even North America to reside and feed. Two of six Green turtles remained in the BHS to reside and feed during inter-nesting periods.
- Increased terrestrial input and sedimentation to beaches is increasing sand temperature 1o C and potentially altering hatching success and sex ratios.
- Olive Ridley turtles are at risk of being hooked by longline fisheries operating in the Western Pacific, Banda and Aru Seas.
- Important turtle nesting beaches should be protected from poaching by setting up community patrols, community based monitoring, and local community agreements to stop harvesting of eggs and hunting of adults.
- It is important to protect turtle nesting beaches and foraging grounds (seagrass beds) from the impacts of coastal development by a) ensuring sand mining, seawall, road or other construction activities do not occur in areas of turtle nesting beaches b) protecting beach and dune vegetation, especially large trees, and c) protecting nesting beaches and foraging grounds from sedimentation associated with coastal development and mining.
- Collaborate with provincial and national fisheries authorities to enforce the use of turtle-excluder devices for trawls in the Arafura Sea, and introduce regulations requiring circle hooks for long lines throughout the BHS and Eastern Indonesia.
- Local fisheries authorities should prohibit the use of passive fishing gear (gill nets, pound nets, beach seine) from an area within 50 km of nesting beaches, and in seagrass beds.
- Establish a municipal trash disposal system that prevents any trash from reaching the ocean or beaches. Create a public campaign against litter, particularly in Sorong, Manokwari, Kaimana, Waisai, and on all passenger ferries.
- Encourage shipping lanes in the BHS to avoid inter-nesting areas at a vicinity of 15 km from nesting beaches to protect turtles during their peak nesting period (Hawksbill and Green turtles: April and September; Leatherbacks: June/July; Olive ridleys: March/April).
- In case of necessary nest relocation, follow best practices to ensure physical conditions lead to high hatching success and even sex ratio. Protocols for nesting beach management has been developed by WWF and can be accessed at: www.wwf.or.id/about_wwf/ whatwedo/marines_species/publication or contact WWF and University of Papua for the most recent practices.
– Adnyana I.B., I.M. Jayaratha, 2009. Post-Nesting Migrations of Olive Ridley Turtles (Lepidochelys olivacea) from The Bird’s Head Peninsula of Papua,
Indonesia. Udayana University, Bali. Indonesia. Brief Technical Report.
– Adnyana I. B., C. Hitipeuw, 2009. Nesting Beach Monitoring Manual. WWF-Publication in Bahasa Indonesia. www.wwf.or.id/berita_fakta/publications/?
– Benson, S.R., P.H. Dutton, C. Hitipeuw, B. Samber, J. Bakarbessy, D. Parker, 2007.Post-Nesting, Migrations of Leatherback Turtles (Dermochelys
coriacea) from Jamursba-Medi, Bird’s Head Peninsula, Indonesia Chelonian Conservation and Biology 6(1):150-154.
– Hitipeuw, C., P.H. Dutton, S.R. Benson, J. Thebu, J. Bakarbessy, 2007. Population status and internesting movement of leatherback turtles, Dermochelys
coriacea, nesting on the northwest coast of Papua, Indonesia. Chelonian Conservation and Biology 6(1):28–36.
– Troeng, S., M. Chaloupka, 2007. Variation in adult annual survival probability and remigration intervals of sea turtles. Marine Biology, 151(5): 1721-