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 humanmade 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 and 12,000 dFAD trajectories in the Atlantic Ocean 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 21% to 40% (depending on effort redistribution after closure) 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 Indian Ocean, and in an elongated strip of areas adjacent to the western African coast for the Atlantic Ocean. 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. Highlights► dFAD beaching rate increased dramatically over 2008-2013 and then stabilized at ~18%. ► dFAD beaching locations clearly identify coastal beaching hotspots. ► Beaching risk depends on the upper ocean circulation and its seasonal variability. ► Prohibiting dFAD deployments in the highest risk areas significantly reduces beaching. ► Spatial closure optimization can account for seasonal variability in beaching risk.

An integrated scheme for the management of drifting fish aggregating devices in tuna purse seine fisheries

“…However, area closure may reduce the potential of beaching in sensitive marine habitats. For example, 21%-40% of beaching could be prevented if deployments were prohibited in riskiest areas, and hotspots for beaching did not coincide with areas of high dFAD deployment activities, thus causing relatively minimal impact of area closure on fisheries (Imzilen et al, 2021). However, spatial and temporal dynamics of beaching are highly dependent on regional geography and oceanography.…”

Sources of marine debris for Seychelles and other remote islands in the western Indian Ocean

“…Drifting Fish Aggregating Devices (dFADs) are buoyant drifters used primarily by purse-seine fisheries to aggregate tuna. The majority of these dFADs are tracked remotely using satellite-transmitting GPSequipped buoys and, as a result, dFADs are one of the only types of marine debris that can be tracked directly from source to sink Imzilen et al (2021). Macmillan et al (2022) identified over 3000 dFAD beaching events across Seychelles, and analysed beaching rates and seasonality.…”

“…As a result, whilst there are indications from bottle labels, no quantitative estimates exist for the relative importance of sources of debris for Seychelles, along with other remote island groups in the western Indian Ocean. Good constraints exist on source regions for one specific type of fishing gear, drifting Fish Aggregating Devices (dFADs), accumulating on Seychelles' beaches (Macmillan et al, 2022;Imzilen et al, 2021), but this has not been generalised to all marine-based sources of debris. The primary purpose of this study is to provide environmental practitioners working with remote western Indian Ocean islands with a first quantitative estimate for debris sources, and to make available a product that can be adapted to future improved constraints on marine debris physics.…”

A standard processing framework for the location data of satellite-linked buoys on drifting fish aggregating devices

“…Gerritsen and Lordan 2011;Hintzen et al, 2012;Lambert et al, 2012;Lee et al, 2010), the design of a standardized framework to capture the heterogeneity that typifies DFAD-related data for their integration into research and management processes is now emerging as a key priority. Buoy location data, in particular, are critical to achieve some of the major objectives of DFAD management; including estimating and monitoring the actual number of DFADs at sea (Chassot et al, 2019;Escalle et al, 2021;Gershman et al, 2015), improving the conservation measures regarding DFAD limitations and their enforcement by fishermen (Goñi et al, 2017;Lennert-Cody et al, 2018), or defining strategies to mitigate their stranding in sensitive areas (Curnick et al, 2020;Davies et al, 2017;Escalle et al, 2021Escalle et al, , 2019Imzilen et al, 2022Imzilen et al, , 2021. Hence, a processing framework to transform this vast amount of industrial data into harmonized information, notably through standard procedures, independent of the characteristics of the databases, appears to be of primary importance.…”