Global spatio-temporal patterns in tropical tuna purse seine fisheries on drifting fish aggregating devices (DFADs): Taking a historical perspective to inform current challenges

Abstract

-This study provides a historical overview of the use of drifting fish aggregating devices (DFADs) in purse seine fisheries since the early 1990s, using global tuna fisheries datasets from the four tuna Regional Fisheries Management Organizations (RFMOs). Tropical tuna purse seine fisheries typically target large yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tunas on free-swimming schools and skipjack (Katsuwonus pelamis) and juveniles of yellowfin and bigeye associated with drifting objects. DFADs have enabled global skipjack catches to markedly increase, and have also introduced major scientific issues for all tuna-RFMOs. In particular, they have strongly modified the fishing strategies of purse seiners that fish on a combination of free-swimming and DFAD-associated schools. Consequently, the cumulated search time traditionally used to quantify nominal fishing effort to assess the status of tuna stocks is inconsistent and cannot be used to derive time series of abundance indices from catch-per-unit of-effort (CPUE). In addition, the lack of information available on the construction, deployment, and use of DFADs has prevented effective monitoring of the fishing pressure over the last two decades exerted by purse seine fleets using this fishing mode. Juveniles of tropical tunas represent a substantial proportion of purse seine catch on DFADs in the three oceans, which has raised particular concern for some bigeye stocks that have been subject to overfishing in the past. Catches of juvenile tunas by DFAD fishing may also result in a decrease in recruitment for fisheries that target adult tunas such as longliners. In addition, some demographic parameters of tunas and other species associated with DFADs may be affected by the resultant habitat modification arising from the widespread deployment of DFADs. Evidence in the literature and provided by the ratio-estimator method suggest that fishing DFAD-associated schools may result in about 100 000 t of bycatch and discards annually. In addition, there is further potential for ghost fishing related mortality of sensitive species such as marine turtles and pelagic sharks. In this context and following a precautionary approach, we finally discuss the increasing need for all tuna-RFMOs to reduce, or at least monitor and control, the use of DFADs to mitigate their adverse effects not only on yellowfin and bigeye stocks but also on open-ocean ecosystems.

Use of video monitoring to quantify spatial and temporal patterns in fishing activity across sectors at moored fish aggregating devices off Puerto Rico

“…Moored and drifting FADs (mFADs and dFADs) are now commonly utilized by all major fishing sectors (e.g. industrial, semiindustrial, artisanal and recreational) throughout all tropical and sub-tropical regions of the ocean , Fonteneau et al 2013, Gershman et al 2015. While industrial fleets that utilize dFADs are required to report associated catch and effort to regional fishery management organizations, comparable quantitative estimates of mFAD catch and effort do not exist, and while thought to be a fraction of those associated with dFADs (Dempster and Taquet 2004), the figures are still substantial due to the sheer magnitude of use around the world (Itano et al 2004, Taquet 2013.…”

Marine pollution originating from purse seine and longline fishing vessel operations in the Western and Central Pacific Ocean, 2003–2015

“…Lost or discarded FADs in the marine environment can be harmful to marine life through ghost fishing, entanglement and acting as habitat for the spread of invasive species (Macfadyen et al 2009;Fonteneau et al 2013;Davies et al 2014). They also have the potential to wash ashore onto coastlines and reefs as marine debris (Greenpeace 2015;Sagapolutele 2015).…”

Fishery management, development and food security in the Western and Central Pacific in the context of climate change

“…WCPO fisheries are diverse, with participating fleets utilizing longline, purse seine, troll, pole and line, handline, and other gears. Highly effective anchored and drifting Fish Aggregating Devices (FADs) are increasingly utilized with great effect and major bycatch (Fonteneau et al, 2013;Hallier and Gaertner, 2008;Leroy et al, 2013).…”