The catch with French Polynesia’s long-line fisheries

Nestled in the middle of the Pacific Ocean, with the nearest land mass thousands of miles away, French Polynesia is a mosaic of 118 islands and atolls. Picture white sandy beaches, juxtaposed by dark volcanic mountains, and atolls where snorkelling with humpback whales is commonplace. Due to the underwater paradise provided by its deep blue lagoons, French Polynesia is renowned for famous diving spots and being a world-class destination to spot the elusive tiger shark (Galeocerdo cuvier). Every year, countless shark fanatics congregate in Fakarava to swim amongst schools of nurse, hammerhead and tiger sharks.

Like most shark species, tigers are vulnerable to exploitation, harvested for their fins, skin and the high content of vitamin A, found in their liver, which can be manufactured into vitamin oil. Similarly, they show life history traits of slow regeneration times meaning that if populations decrease dramatically, the chance of recovery is small. For now, tiger sharks are classified as near threatened by the International Union for Conservation of Nature, and a protected species in this area of the world. They therefore cannot legally be targeted for harvest by fisheries, providing a glimmer of hope for the long-term fate of this species.

Despite this, due its geographic position French Polynesia has a high potential for fisheries and has led to many interactions between the sharks and fishermen. A recent study found 38% of sharks recorded in the Vallee Blanch ecotourism site, have at least one fishery interaction in their lifetime. For large sharks, the direct trauma of a hook puncture is unlikely to have a significant effect, with a survival rate greater than 97%. However, retention times of hooks are relatively unknown and could affect survival rate post-release. In the worst case, stainless steel hooks can stay implanted for seven years, increasing chance of further entanglement and potentially obstructing feeding. Worryingly the scientists have not yet been able to identify the origin of hooks or whether lines are cast by local or remote fishermen. Furthermore, tiger sharks are migratory and hooks could be embedded anywhere on a long seasonal migration.

The use of photo identification has capitalised on tiger shark tourism, allowing individuals to be identified and hook retention logged, thus providing an insight for scientists. Studies around photo identification supported by satellite tagging show spatial movement in the region would complement this further by identifying hotspots for fishermen and tiger shark interaction. This will assist in the implementation of mitigation strategies such as the use of corrodible hooks, which has shown success in various Australian and US fisheries. The encouraging cooperation of fishermen and scientists provide optimism for the future existence of our sharks.

Pelorus has teamed up with leading shark scientists and local dive specialists to assess the ecological role of tiger sharks in French Polynesia. The project focuses on deploying satellite and acoustic tags, equipped with video cameras to capture never before seen mating behaviour and habitat selection. This research aims to close knowledge gaps and assess movement patterns within the archipelago, to determine the potential for regional adaptation and draw comparisons with the Hawaiian population.