Spatial management can significantly reduce dFAD beachings in Indian and Atlantic Ocean tropical tuna purse seine fisheries

Abstract

Debris from fisheries pose significant threats to coastal marine ecosystems worldwide. Tropical tuna purse seine fisheries contribute to this problem via the construction and deployment of thousands of man-made drifting fish aggregating devices (dFADs) annually, many of which end up beaching in coastal areas. Here, we analyzed approximately 40 000 dFAD trajectories in the Indian Ocean (IO) and 12 000 dFAD trajectories in the Atlantic Ocean (AO) deployed over the decade 2008-2017 to identify where and when beachings occur. We find that there is tremendous promise for reducing beaching events by prohibiting deployments in areas most likely to lead to a beaching. For example, our results indicate that around 40% of beachings can be prevented if deployments are prohibited in areas in the south of 8°S latitude, the Somali zone in winter, and the western Maldives in summer for the IO, and in an elongated strip of areas adjacent to the western African coast for the AO. In both oceans, the riskiest areas for beaching are not coincident with areas of high dFAD deployment activity, suggesting that these closures could be implemented with relatively minimal impact to fisheries. Furthermore, the existence of clear hotspots for beaching likelihood and the high rates of putative recovery of dFAD buoys by small-scale fishers in some areas suggests that early warning systems and dFAD recovery programs may be effective in areas that cannot be protected via closures if appropriate incentives can be provided to local partners for participating in these programs.

Quantifying the increase in fishing efficiency due to the use of drifting FADs equipped with echosounders in tropical tuna purse seine fisheries

“…Our results convincingly demonstrate how and when the use of echosounder buoys in- This increasing trend highly suggests that the benets of using this technology have been sucient to cause shers to change shing strategy from one in which random encounters of foreign FOBs and free schools were important components of overall shing eort to a strategy increasingly directed towards the vessel's own FOBs for which the sher has access to echosounder information. The potential contribution of this change to the recent increase in dFAD deployments (Lopez et al 2017, Imzilen et al 2020) is an important avenue for future research.…”

“…Buoys from the manufacturer Marine Instruments, which dominate French deployments from 2012 onward, also included echosounder data, if the buoy had one, and a list of vessel or company names with access to the buoy trajectory and echosounder data. Buoy positions were classied into onboard and in the water positions using a random forest algorithm based primarily on buoy speed, water temperature and timestep between successive positions (Maufroy et al 2015, Imzilen et al 2020.…”