Deactivated drifting fish aggregating devices (dFAD) are commonly deployed to attract tuna and facilitate their capture, but their impact on marine ecosystems and debris generation remains a critical environmental concern.
Understanding deactivated dFADs
Tropical tuna purse-seine fisheries around the world deploy more than 100,000 dFADs annually. These devices, equipped with satellite-transmitting GPS buoys, can be deactivated remotely—often when they drift out of fishing zones or into areas inaccessible to large vessels. Once deactivated, these buoys typically stop transmitting location data to fishermen and scientists, leading to significant gaps in our understanding of their environmental impact. However, these buoys continue to function, collecting data that, until now, has largely gone unreported.
A unique dataset reveals new insights
From 18 July–7 August 2020, scientists had access to a unique dataset: position information from buoys that had been deactivated but continued to transmit data to buoy manufacturers. This provided a rare glimpse into the "afterlife" of dFADs, revealing not only their continued journey but also their potential to strand along coastlines, posing risks to marine habitats.
Key findings from the study:
- Increased detection of dFADs: Deactivated buoys accounted for an average 17.2% increase in daily detected dFADs during the study period, illustrating a significant undercount in traditional surveys.
- Impact on stranding rates: Inclusion of these deactivated buoys led to a 23.7% increase in detected strandings, highlighting the importance of monitoring these devices even after deactivation.
- Stranding motivations: Half of the buoys deactivated before stranding were in shallow waters less than 50 meters deep, indicating that the risk of stranding motivates many deactivation decisions. This suggests a preventive approach to environmental management.
- Lifespan of deactivated buoys: The estimated half-life of these buoys—101.3 days—aligns with previous studies, suggesting a prolonged period during which these devices can impact marine environments even after their operational use has ended.
Implications for future management
This study underscores the critical need for continuous tracking of all dFADs, regardless of their operational status. By ensuring that deactivated dFADs remain part of our observational datasets, scientists and policymakers can more accurately assess and mitigate their environmental impacts. This approach not only improves our understanding of dFAD dynamics but also enhances our ability to protect marine ecosystems from the unintended consequences of industrial fishing practices.
Read the full paper, First look at the distribution of deactivated dFADs used by the French Indian Ocean tropical tuna purse-seine fishery, in ICES Journal of Marine Science.
