Potential environmental impacts caused by beaching or drifting fish aggregating devices and identification of management solutions and uncertainties

Drifting fish aggregating devices (dFADs) are widely used in tropical tuna purse seine fisheries to aggregate fish and make them easier to catch. The use of dFADs has been associated with a number of potential positive and negative impacts, touching on a range of ecological, economic and social issues. One negative environmental impact of dFADs is that they have the potential to wash ashore and become grounded or beached, potentially causing damage to marine habitats. However, other than anecdotal reports, this issue has received very little research attention to date. The lack of research on this topic means that the problem of beaching dFADs is not well defined, with the risk of beaching events mostly assumed and the extent and severity of impacts uncertain. The aim of this paper is to better characterise the potential problem of beaching dFADs. We examine the potential for dFAD beaching events to occur, which is determined by location of deployment, dispersal patterns, extent of efforts to prevent beaching events from occurring and, to a lesser extent, dFAD design. This discussion is illustrated with a case study examining the spatio-temporal dynamics of dFAD trajectories in the Indian Ocean and estimating the frequency of dFAD beaching events on coral reefs. The potential environmental impacts of beached dFADs are reviewed by looking at wider literature on other abandoned, lost, or otherwise discarded fishing gear, and we offer some thoughts on the classification of dFADs as marine pollution. Finally, we critically discuss a number of possible ways to reduce the number of dFAD beaching events on sensitive marine habitats. This includes regulatory measures, which would be applied by the tropical tuna Regional Fisheries Management Organisations or coastal and island state governments and advances in dFAD design, which would likely come from collaboration between fishing companies, researchers and NGOs/non-profit partnerships. Possible measures include reducing the overall number of dFADs in the water, i.e. though deployment limits, fee structures and reduced fleet capacity, or a localised reduction of dFAD deployments in sensitive areas; reduced lifetime of dFADs, through use of entirely bio-degradable materials; and the prevention of dFADs entering areas with sensitive habitats, through recovery initiatives (at sea and inshore) and innovative dFAD design