F I S H and F I S H E R I E S , 2013, 14, 391–415 Is it good or bad to fish with FADs? What are the real impacts of the use of drifting FADs on pelagic marine ecosystems? Laurent Dagorn1, Kim N. Holland2, Victor Restrepo3 & Gala Moreno4 1Institut de Recherche pour le De´veloppement (IRD), UMR 212, PO Box 570, Victoria, Seychelles, 2Hawaiian Institute of Marine Biology (HIMB), University of Hawaii, PO Box 1346, Kaneohe, HI, 96744, USA, 3ISSF, 805 15th Street NW, Washington, DC, 20005, USA and 4AZTI-Tecnalia/Herrera Kaia., Portualdea, z/g, 20110, Pasaia, Gipuzkoa, Spain Abstract Correspondence: The use of fish aggregating devices (FADs) by purse seine fisheries has come under Laurent Dagorn, Institut de Recherche increasing criticism for its potential deleterious impacts on tuna stocks, for high pour le De´veloppe- levels of by-catch and threats to the biodiversity of tropical pelagic ecosystems. ment (IRD), UMR Here, we review the current state of scientific knowledge of this fishing technique 212, PO Box 570, and current management strategies. Our intent is to encourage objective discussion Victoria, Seychelles of the topic and highlight areas worthy of future research. We show that catching Tel/Fax: +248 4224 742 juvenile tuna around FADs does not necessarily result in overfishing of stocks, E-mail: laurent. although more selective fishing techniques would likely help obtain higher yield. [email protected] 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 threa- Received 7 Nov tened. Accordingly, to minimize impacts on ecosystem balance, there is merit in 2011 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 repre- sent 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 fish- ing could be an ecologically and economically sensible fishing method. Keywords By-catch, ecological trap, FAD, purse seine, tuna Introduction 392 Purse seine fishing on floating objects 394 Impacts on tuna stocks 395 Impacts on non-target species: by-catch 399 Impacts on habitats and ecological consequences 401 The route towards the sustainable use of drifting FADs 407 Monitoring the numbers of electronic buoys and numbers of FADs (FAD management plans) 407 Reducing fishing mortality of juvenile bigeye and yellowfin tuna 408 © 2012 John Wiley & Sons Ltd DOI: 10.1111/j.1467-2979.2012.00478.x 391 Are FADs bad? L Dagorn et al. Reducing the fishery-induced mortality of by-catch 409 Conclusion 411 Acknowledgements 412 References 412 This study discusses only the industrial use of Introduction drifting FADs. The use of FADs by purse seine Many species of marine fishes aggregate around fleets started in the 1980s and rapidly expanded floating structures such as drifting logs or palm throughout the early 1990s. In the remainder of fronds (Castro et al. 2002; Taquet et al. 2007). this review, the term ‘FAD’ refers to any man- This behaviour was first reported in 200 AD in made floating object built for the purpose of fish- the Mediterranean, when the Roman author Op- ing, whereas the term ‘log’ refers to any natural pian described the use of floating objects to catch object and the term ‘floating object’ is used when dolphinfish (Coryphaena hippurus, Coryphaenidae) referring to both FADs and logs. (cited in Dempster and Taquet 2004). In the late The use of drifting FADs by the purse seine fish- 1950s, the first tuna (Scombridae) purse seiners ery raises the possibility of three potential negative operating in the eastern Pacific Ocean found it impacts: (i) reduction in yield per recruit of target was feasible to capture schools of tunas associated species (tunas), (ii) increased by-catch and pertur- with natural floating objects such as logs (Hall bation of pelagic ecosystem balance and (iii) dele- 1998). Thereafter, industrial tuna purse seiners terious alteration of the normal movements of the increasingly focussed on using drifting floating species associated with FADs (Fonteneau et al. objects to expedite and augment their catches. 2000; Bromhead et al. 2003; Morgan 2011). There are two main reasons for this focus. First, First, let us address the issue of how FADs might because floating objects are visible at the surface contribute to overfishing of tuna stocks. Although (or their positions are already known – see below), FAD catches are usually mainly comprised of adult they help fishers reduce the search time required skipjack tuna (Katsuwonus pelamis, Scombridae), to locate fish schools. Finding and keeping track of they are also usually characterized by the co- floating objects has been further advanced by occurrence of small yellowfin (Thunnus albacares, attaching radio beacons or satellite-linked GPS Scombridae) and bigeye (T. obesus, Scombridae) units. This permits tracking in real time and from tuna (although there are large regional and sea- great distances. Recently, the practice of attaching sonal variations in the co-occurrence of these spe- satellite-linked echosounder fish finder units to cies). By contrast, purse seine catches on free- floating objects further improves efficiency by swimming schools are typically dominated by informing fishers as to which ones might have fish large yellowfin tuna and skipjack tuna. Because of underneath and are then worth visiting. Second, the common presence of small bigeye and yellow- floating objects increase the vulnerability of tunas fin tuna in sets on floating objects, this practice, if to fishing; sets around floating objects have higher not managed, could affect the yield per recruit of success rates (90%) than those made on free- these species and could lead to excessive reduction swimming schools (50%) (Fonteneau et al. 2000; of stocks. Suzuki et al. 2003; Miyake et al. 2010). Because Second, FADs also attract non-tuna species floating objects provided such a major increase in (Hunter and Mitchell 1967), and these species are the catchability of tunas (Marsac et al. 2000), fish- taken when purse seiners fish on FADs (Hall ers started to construct and release artificial fish 1998; Romanov 2002; Amande` et al. 2010). aggregating devices (FADs). There are two basic Thus, the capture of non-target species associated categories of FADs – anchored and drifting. with floating objects could negatively impact biodi- Anchored FADs are primarily (although not exclu- versity either by removing by-catch species in sively) used in small-scale coastal, semi-artisanal unsustainable quantities or by selective removal of and sport fisheries, whereas open ocean drifting some components of the pelagic ecosystem. In con- FADs are used by industrial purse seine fisheries. trast, free-swimming school sets are usually char- 392 © 2012 John Wiley & Sons Ltd, F I S H and F I S H E R I E S , 14, 391–415 Are FADs bad? L Dagorn et al. acterized by low amounts of by-catch of non-target tional Commission for the Conservation of Atlantic species. However, even though by-catch at FADs Tunas, ICCAT, the Indian Ocean Tuna Commis- may be quite small, the fact that fishing on float- sion, IOTC, and the Western and Central Pacific ing objects is a part of the fleet’s overall strategy Fisheries Commission, WCPFC) have implemented results in an increase in by-catch for the purse several measures to regulate the use of FADs seine fishery as a whole (Romanov 2002). (Table 1), and some research projects dedicated to Finally, the release of large numbers of FADs in FADs have been conducted. However, major gaps the ocean could change the natural environment in knowledge still exist, and there is a need to of tunas. The potential effects of such habitat mod- review what is known about the impacts of FAD ification on the behaviour and biology of tunas fishing and to investigate new management mea- have been grouped under the ‘ecological trap’ sures. hypothesis (Marsac et al. 2000; Hallier and Gaert- The objective of this study is to review the cur- ner 2008). This hypothesis contends that deploy- rent knowledge about tropical tuna purse seine ing FADs in unnaturally large numbers could fisheries and the relevant aspects of the biology either entrain tuna in locations that they might and behaviour of species that associate with float- normally leave or, conversely, take them to places ing objects. More than 60% of the literature on to which they would not normally go, thereby FADs (combining drifting and anchored FADs, impacting negatively their biology (e.g. growth Dempster and Taquet 2004) are non-peer- rate or reproductive success). reviewed articles, with a large portion being work- After reviewing these potential impacts, Fonte- ing documents presented at Tuna RFMOs meet- neau et al. (2000) and Bromhead et al. (2003) ings. A decade after the reviews by Fonteneau concluded that, owing to the lack of quantitative et al. (2000) and Bromhead et al. (2003), we aim data, potential negative long-term effects of FADs to present the scientific and management progress on tuna stocks and pelagic ecosystems were diffi- made in this field, providing an evaluation of what cult to evaluate and remained hypothetical. How- is actually known and what is not known. We ever, they cautioned that the continuing use of hope to encourage objective discussion of the good FADs at a large scale could have detrimental and bad features of fishing on floating objects and effects.