Is it good or bad to fish with FADs? What are the real impacts of the use of drifting FADs on pelagic marine ecosystems?

Abstract

The use of fish aggregating devices (FADs) by purse seine fisheries has come under increasing criticism for its potential deleterious impacts on tuna stocks, for high levels of by‐catch and threats to the biodiversity of tropical pelagic ecosystems. Here, we review the current state of scientific knowledge of this fishing technique and current management strategies. Our intent is to encourage objective discussion of the topic and highlight areas worthy of future research. We show that catching juvenile tuna around FADs does not necessarily result in overfishing of stocks, although more selective fishing techniques would likely help obtain higher yield. Levels of non‐tuna by‐catch are comparable to or less than in other commercial tuna fisheries and are primarily comprised of species that are not considered threatened. Accordingly, to minimize impacts on ecosystem balance, there is merit in considering that all species captured in purse seine fisheries (excluding vulnerable species such as turtles and sharks) should be retained, but the consequences of such a measure should be carefully examined before implementation. The take of vulnerable species could be further reduced by introduction of additional mitigation measures, but their potential benefits would be limited without parallel efforts with other gears. Finally, there is no unequivocal empirical evidence that FADs represent an ‘ecological trap’ that inherently disrupts tuna biology although further research should focus on this issue. We encourage RFMOs to expand and improve their FAD management plans. Under appropriate management regimes, FAD fishing could be an ecologically and economically sensible fishing method.

A critique of the ecosystem impacts of drifting and anchored FADs use by purse-seine tuna fisheries in the Western and Central Pacific Ocean

“…A particularly important aspect for future investigation will also be how FAD density affects tuna behaviour and whether "ecological trap" hypotheses (Marsac et al 2000;Hallier and Gaertner 2008) are valid for the WCPO. The recent review of the global impacts of FADs on tuna highlighted the need for hypotheses associated with FAD density to be tested in multiple oceans (Dagorn et al 2012). Combined with improved understanding of the impacts of FADs on individual and stock-wide biology, this knowledge will inform management decisions on the impacts of FADs within the WCPO.…”

“…Purse seine sets on floating objects are also more fuel efficient relative to free school sets (Suuronen et al 2012). These circumstances help create greater stability in effort and catches for purse-seine operators (Dagorn et al 2012). The distribution of natural floating objects such as logs, or large megafauna is variable across the ocean and their presence is not always predictable even a Corresponding author: brunol@spc.int within an area where floating objects are likely to occur in higher densities (Dagorn et al 2012).…”

“…These circumstances help create greater stability in effort and catches for purse-seine operators (Dagorn et al 2012). The distribution of natural floating objects such as logs, or large megafauna is variable across the ocean and their presence is not always predictable even a Corresponding author: brunol@spc.int within an area where floating objects are likely to occur in higher densities (Dagorn et al 2012). Consequently the use of artificial fish aggregating devices (FADs) has increased, which has reduced the uncertainty of finding floating objects and generated new opportunities to fish with greater reliability in all oceanic areas.…”

“…Two types of FADs have been deployed: drifting FADs (dFADs) which are used in most purse-seine tuna fisheries across the globe; and anchored FADs (aFADs) which for purse-seine tuna fishing are unique to the WCPO and deployed specifically in the archipelagic waters in the western sector (Williams and Terawasi 2011;Dagorn et al 2012).…”

An individual-based model of skipjack tuna ( Katsuwonus pelamis ) movement in the tropical Pacific ocean

“…However, like animal movement, real fishing operations occur at the scale of individual boats and fleets that also have their own individual behaviours. While spatial and temporal aggregation may be sufficient to capture the experienced mortality in some cases, feedbacks between fishers and fish, such as occur with the use of free-floating fish aggregating devices in tuna fisheries, may cause significant local-scale changes to both fleet and tuna behaviour (Dagorn et al, 2013;Leroy et al, 2013b;Maufroy et al, 2016). More broadly, the incorporation of IBMs alongside Eulerian models as two components of a hybrid-approach that have the flexibility of robust parameter estimation, yet can examine dynamics across varying spatiotemporal scales should be developed for modelling of marine species distribution (Rose et al, 2015;Tyutyunov and Titova, 2017).…”