The Significance of Crab Island’s Flatback Sea Turtles

Most major sea turtle rookeries in the world have received some level of scientific attention to assess the status of the nesting population. Most are well known. However, Crab Island remains a scientific mystery despite the fact that it supports the world’s largest nesting population of the threatened flatback sea turtle.

Crab Island was first reported in 1972 during initial assessments to be of world significance for flatback sea turtles. Numbers nesting at Crab Island are significantly larger than any other nesting site and remains the most internationally important site known for the species. It is thought to support the majority of the nesting population of flatback sea turtles. Threats to this rookery threaten the species as a whole. However, the current status is unknown, the threats to the population have not been quantified and conservation management is uninformed.

The turtles face an uncertain future. Assessments on the mainland have identified predation by feral pigs and goannas on close to 100% of nests laid, meaning no eggs are hatching. Sea turtles will also be one of the first species impacted by climate change – incubation is very dependent of temperature. A change of only a couple of degrees will result in high mortalities or skewed sex ratios. On low lying beaches like Crab, sea level rise is a concern, as is sea temperature change resulting in impacts to feeding habitats. The island’s close proximity to Bamaga and Thursday Island warrants further monitoring to identify harvesting levels. Anecdotal evidence suggests eggs are collected on a regular basis and some adult turtles are also harvested. Unlike most rookeries in Australia the island is not offered any formal protection and is not located within a marine park. There is no active management of the island or restrictions placed on access. As visitation to Cape York increases areas like Crab Island are becoming more and more popular as a destination. It is also unclear whether commercial fishing operations are having an impact on feeding or nesting turtles within their range. Their choice of habitat may see them come in to conflict with commercial fishing operations and while the use of TEDs (Turtles exclusion Devices) on commercial fishing vessels has reduced turtle bycatch there is still a major issue of turtles being caught in discarded nets or ‘ghost nets’ from illegal foreign fishing vessels.

Baseline data is necessary to determine what the current status of the population is and to identify any trends. This study hopes to inform the process by providing valuable biological data, as well as prompt actions which increase the protective status of the population.