Modelling drifting FADs trajectories arriving at essential habitats for sea turtles in the Pacific Ocean
Purse seine fishers extensively deploy drifting Fish Aggregating Devices (FADs) to aggregate and catch tropical tuna, with 46,000 to 65,000 FADs deployed in the Pacific Ocean annually, and 16,000–25,000 FADs in the eastern Pacific Ocean (EPO) only. Main concerns related to the loss and abandonment of FADs are i) marine pollution; ii) the potential risk of entanglement of sea turtles and other marine fauna in FAD netting while drifting at sea or when stranded; and iii) the potential to cause ecological damage to vulnerable ecosystems via stranding events, including reefs, beaches, and other essential habitats for sea turtles. To explore and quantify the potential connectivity between FADs and important oceanic or coastal sea turtles habitats in the Pacific Ocean, a series of passive-drift Lagrangian simulation experiments were undertaken based on possible FAD drifting behaviour. Corridors of connectivity between industrial FAD fishing grounds and zones of important habitats for sea turtles were identified. For FADs deployed in the EPO, the main areas of concern appear to be the turtle habitats in the south-eastern Pacific Ocean, corresponding to oceanic leatherback turtle (Dermochelys coriacea) migration and feeding grounds. Moderate accumulation of FADs was also detected in the equator, coastal and oceanic habitats and nesting sites around Mexico, Costa Rica and Panama. Finally, a large equatorial area, south of Hawaiʻi, important leatherback turtle foraging habitat, exhibited large numbers of FADs transiting when deployed in the equatorial zones north of the equator, from both the EPO and WCPO. It should be noted that the connectivity patterns detected appear to be somewhat mitigated against by the current deployment distribution of FADs in the EPO. Additional research and analyses should be performed i) to better understand at-sea interactions between FADs and sea turtle populations and potential entanglements; and ii) to quantify the likely changes in connectivity and distribution of FADs within the equatorial fishing grounds and higher latitude sea turtle habitats, under proposed non-entangling and Biodegradable FAD measures or changes in FAD deployment strategies.
Note: This paper was published, with a different introduction, as IOTC-2022-WGFAD03-12 (attached).