Fish aggregating devices drift like oceanographic drifters in the near-surface currents of the Atlantic and Indian Oceans

TL;DR

This study shows that fish aggregating devices (FADs) used in tuna fisheries can serve as cost-effective, satellite-tracked surface drifters, providing valuable near-surface current data comparable to traditional oceanographic drifters.

Contribution

It demonstrates that FADs, equipped with GPS, can reliably measure near-surface currents, offering a new, cost-effective data source for oceanographic research and global observing systems.

Findings

FADs' surface velocities are highly correlated with drifters in Atlantic and Indian Oceans.

Subsurface structures of FADs cause measurable slowing, especially in the Atlantic.

Fishermen's data can supplement and enhance existing ocean surface current datasets.

Abstract

Knowledge of ocean surface dynamics is crucial for oceanographic and climate research. The satellite-tracked movements of hundreds of drifters deployed by research and voluntary observing vessels provide high-frequency and high-resolution information on near-surface currents around the globe. Consequently, they constitute a major component of the Global Ocean Observing System (GOOS). However, maintaining this array is costly and in some oceanic regions such as the tropics, spatio-temporal coverage is limited. Here, we demonstrate that the GPS-buoy equipped fish aggregating devices (FADs) used in tropical tuna fisheries to increase fish catchability are also capable of providing comparable near-surface current information. We analyzed millions of position data collected between 2008 and 2014 from more than 15,000 FADs and 2,000 drifters, and combined this information with remotely-sensed near-surface current data to demonstrate that the surface velocity components of FADs and drifters are highly correlated in the Atlantic and Indian Oceans. While it was noted that the subsurface structures of FADs (typically made of recycled fishing nets) did slow them down relative to the drifters, particularly in the Atlantic Ocean, this bias was measurable and could be accounted for in future studies. Our findings show that the physical meteorological and oceanographic data collected by fishermen could provide an invaluable source of information to the GOOS. Furthermore, by forging closer collaborations with the fishing industry and ensuring their contributions to global ocean databases are properly acknowledged, there is significant scope to capture this data more effectively.