Large-Scale Examination of Spatio-Temporal Patterns of Drifting Fish Aggregating Devices (dFADs) from Tropical Tuna Fisheries of the Indian and Atlantic Oceans

Since the 1990s, massive use of drifting Fish Aggregating Devices (dFADs) to aggregate tropical tunas has strongly modified global purse-seine fisheries. For the first time, a large data set of GPS positions from buoys deployed by French purse-seiners to monitor dFADs is analysed to provide information on spatio-temporal patterns of dFAD use in the Atlantic and Indian Oceans during 2007-2011. First, we select among four classification methods the model that best separates at sea from on board buoy positions. A random forest model had the best performance, both in terms of the rate of false at sea predictions and the amount of over-segmentation of at sea trajectories (i.e., artificial division of trajectories into multiple, shorter pieces due to misclassification). Performance is improved via post-processing removing unrealistically short at sea trajectories. Results derived from the selected model enable us to identify the main areas and seasons of dFAD deployment and the spatial extent of their drift. We find that dFADs drift at sea on average for 39.5 days, with time at sea being shorter and distance travelled longer in the Indian than in the Atlantic Ocean. 9.9% of all trajectories end with a beaching event, suggesting that 1,500-2,000 may be lost onshore each year, potentially impacting sensitive habitat areas, such as the coral reefs of the Maldives, the Chagos Archipelago, and the Seychelles

Dispositifs de Concentration de Poissons (DCP) des océans Atlantique et Indien : utilisation, efficacité de pêche et potentialités de gestion

Since the mid 1990s, the use of drifting Fish Aggregating Devices (dFADs) by purse seiners, artificial objects specifically designed to aggregate fish, has become an important mean of catching tropical tunas. In recent years, the massive deployments of dFADs, as well as the massive use of tracking devices on dFADs and natural floating objects, such as GPS buoys, have raised serious concerns for tropical tuna stocks, bycatch species and pelagic ecosystem functioning. Despite these concerns, relatively little is known about the modalities of GPS buoy tracked objects use, making it difficult to assess and manage of the impacts of this fishing practice. To fill these knowledge gaps, we have analyzed GPS buoy tracks provided by the three French fishing companies operating in the Atlantic and the Indian Oceans, representing a large proportion of the floating objects monitored by the French fleet. These data were combined with multiple sources of information: logbook data, Vessel Monitoring System (VMS) tracks of French purse seiners, information on support vessels and Local Ecological Knowledge (LEK) of purse seine skippers to describe GPS buoy deployment strategies, estimate the total number of GPS buoy equipped dFADs used in the Atlantic and Indian Oceans, measure the contribution of strategies with FOBs and support vessels to the fishing efficiency of tropical tuna purse seiners, identify potential damages caused by lost dFADs and finally to propose management options for tropical tuna purse seine FOB fisheries. Results indicate clear seasonal patterns of GPS buoy deployment in the two oceans, a rapid expansion in the use of dFADs over the last 7 years with an increase of 4.2 times in the Indian Ocean and 7.0 times in the Atlantic Ocean, possible damages to fragile coastal ecosystems with 10% of GPS buoy tracks ending with a beaching event and an increased efficiency of tropical tuna purse seine fleets from 3.9% to 18.8% in the Atlantic Ocean over 2003-2014 and from 10.7% to 26.3% in the Indian Ocean. Interviews with purse seine skippers underlined the need for a more efficient management of the fishery, including the implementation of catch quotas, a limitation of the capacity of purse seine fleets and a regulation of the use of support vessels. These results represent a first step towards better assessment and management of purse seine FOB fisheries.Depuis le milieu des années 1990, l’utilisation de Dispositifs de Concentration de Poissons (DCP), des objets artificiels spécifiquement mis à l’eau pour agréger des bancs de poissons, est devenue de plus en plus importante pour la pêche au thon tropical à la senne. Cette utilisation massive des DCP, qui s’accompagne d’une utilisation massive de dispositifs de suivi comme les balises GPS et les balises échosondeurs, est aujourd’hui source d’inquiétude pour les stocks de thons, les prises accessoires mais aussi pour le fonctionnement des écosystèmes pélagiques. Cependant, les modalités d’utilisation des DCP et des balises GPS qui servent à les suivre restent mal connues, ce qui complique considérablement l’évaluation et la gestion des impacts de ces pratiques de pêche. Afin d’améliorer les connaissances actuelles de la pêcherie, les positions des balises GPS utilisées par les 3 armements français dans les océans Atlantique et Indien, constituant une part significative des DCP utilisés dans ces deux océans, ont été analysées. Ces données ont été combinées avec des multiples sources d’information : les livres de bord, les trajectoires VMS des senneurs français ainsi que des entretiens avec les patrons français. Elles nous permettent de mieux comprendre les stratégies de mise à l’eau des DCP et des balises, d’estimer le nombre d’objets flottants utilisés par les flottes de senneurs dans les océans Atlantique et Indien, de mesurer la contribution des DCP et des navires auxiliaires à l’efficacité de pêche des senneurs, d’identifier des destructions potentielles d’habitats par les DCP échoués and pour finir de proposer des solutions de gestion pour la pêcherie. Les résultats montrent une grande saisonnalité dans les mises à l’eau des deux océans, une croissance rapide du nombre de balises GPS au cours des 7 dernières années puisqu’elle est multipliée par 4.2 dans l’Océan Indien et 7 dans l’Océan Atlantique, des dommages possibles causés à des écosystèmes côtiers fragiles avec une probabilité d’échouage de l’ordre de 10% et finalement une augmentation de l’efficacité de pêche entre 2003 et 2014 de l’ordre de 3.8-18.8% dans l’Océan Atlantique et 10.7%-26.3% dans l’Océan Indien. Les entretiens avec les capitaines des senneurs soulignent la nécessité d’une gestion plus efficace de la pêcherie, avec entre autres l’instauration de quotas, une régulation de la capacité de la flotte de senneurs et un meilleur suivi des navires auxiliaires. Les résultats obtenus constituent les premières étapes nécessaires à une meilleure gestion de la pêche sous objet flottan

Effects of the ICCAT FAD moratorium on the tuna fisheries and tuna stocks

International audienceCe document analyse le moratoire de l'ICCAT sur les DCP mis en oeuvre depuis 2013. L'analyse des prises réalisées sous DPC entre 2006 et 2012 a montré que 8,7 % et 5,3 % des captures sous DCP de thon obèse et d'albacore, respectivement, ont été réalisées dans les strates du moratoire. Pour ces dernières années (2013-2014), deux grandes flottilles ont opéré dans la zone : les flottilles de senneurs européens et associés et les navires ghanéens. Les deux flottilles ont bien respecté le moratoire au cours de ces années. La mise en oeuvre du moratoire a entraîné en janvier et février une diminution significative des captures sous DCP de la flottille ghanéenne, mais pas de la flottille européenne, étant donné que, pendant le moratoire, cette flottille pêchait efficacement sous DCP dans d'autres zones de pêche. Il n'y a pas eu de capture plus élevée dans la zone du moratoire en mars 2013-2014 et aucun changement visible dans la pêche en bancs libres. Les prises totales sous DCP ont été élevées au cours de la période 2011-2014. Ce moratoire a eu très peu d'impact en matière de protection des thons juvéniles ; il n'y a aucune preuve que ce règlement puisse améliorer considérablement l'état des stocks. Il conviendrait d'envisager une gestion alternative plus efficace de la pêche sous DCP, des fermetures de zones plus grandes et des mesures visant à réduire la surcapacité actuelle de la pêche sous DCP. RESUMEN Este documento analiza la moratoria de ICCAT a los DCP implementada desde 2013. El análisis de las capturas sobre DCP en 2006-2012 demostró que un 8,7% y un 5,3% de las capturas sobre DCP de patudo y rabil, respectivamente, fueron realizadas en los estratos de la moratoria. Para los años recientes (2013-2014), dos flotas principales han estado operando en la zona: los cerqueros europeos y asociados y los buques ghaneses. Ambas flotas han cumplido bien la moratoria durante estos años. La implementación de la moratoria ha producido un descenso significativo en las capturas de DCP durante enero-febrero para la flota ghanesa, pero no para la flota europea ya que durante la moratoria dicha flota ha pescado de forma eficaz sobre DCP en caladeros alternativos. No se produjeron capturas mayores en la zona de la moratoria en marzo de 2013-2014 y no se produjo ningún cambio visible en la pesca sobre bancos libres. Las capturas totales sobre DCP han sido elevadas durante el periodo 2011-2014. Esta moratoria ha tenido muy poco impacto en la protección de los túnidos juvenilesThis paper analyzes the ICCAT FAD moratorium implemented since 2013. Analysis of FAD catches in 2006-2012 showed that 8.7% and 5.3% of bigeye and yellowfin FAD catches respectively were caught in the moratorium strata. For recent years (2013-2014), two major fleets have been operating in the area: the European and associated purse seiners, and Ghanaian vessels. Both fleets have been well following the moratorium during these years. The moratorium implementation has produced a significant decrease in FAD catches during January February for the Ghanaian fleet, but not for the European fleet, as during the moratorium, this fleet was efficiently fishing on FADs in alternate fishing grounds. There was no higher catches in the moratorium area in March 2013-2014 and no visible change in the free school fishing. Total FAD catches have been high during the 2011-2014 period. This moratorium had very little impact in the protection of juvenile tuna; there is no evidence that this regulation may significantly improve stock status. More efficient alternate management of the FAD fishing should be envisaged, larger closed areas and measures targeting to reduce the today overcapacity of the FAD fishery

Recovery at sea of abandoned, lost or discarded drifting fish aggregating devices

Tropical tuna purse-seine fishing vessels contribute to abandoned, lost or discarded (ALD) fishing equipment by deploying large numbers of drifting Fish Aggregating Devices (dFADs). Here we analysed more than 80,000 dFAD trajectories (56,263 tracking buoys) in the Indian and Atlantic oceans from 2012 to 2018. We found that more than 40% of dFAD trajectories ultimately drifted away from fishing grounds, becoming ALD. About 20% of these lost dFADs passed within 50 km of major ports, indicating that port-based programmes could be effective in collecting ALD dFADs at sea. We also identified areas within the fishing grounds where most dFADs exit and where high-seas recovery could be valuable. For example, most dFADs leaving Indian Ocean fishing grounds along their eastern border at ~70° E, particularly in October–December, do not return to fishing grounds. Despite considerable logistical challenges, at-sea dFAD recovery offers promising options for reducing the ecological footprints of purse-seine fisheries.

Example of vessel (blue line) and buoy (red line) trajectories inferred from VMS and buoy GPS positions, respectively.

<p>After leaving the port of Abidjan (black square) the boat heads to the East in the direction of the Gulf of Guinea, before heading to the West in the direction of Dakar and conducting a series of fishing sets (grey dots). The overlap of the buoy and vessel trajectories indicates that the vessel turned on this particular buoy (1) before entering the port of Dakar. The buoy was likely deployed after leaving the port, shortly after performing a fishing set (2).</p

Smoothed mean densities of observed (as declared in logbooks, a) and predicted dFAD fishing sets (as derived from the corrected RF outputs, b) for the period 2007–2011.

<p>Densities were calculated on a 1° grid and smoothed using the two dimensional density estimation function <i>kde2d</i> of the MASS package in R (bandwidth chosen according to the rule-of-thumb provided in the function <i>bandwith</i>.<i>nrd</i>).</p

Time (a) and distance (b) at sea per ocean (in d and km) as a function of recapture month.

<p>Time (a) and distance (b) at sea per ocean (in d and km) as a function of recapture month.</p

Fishing on floating objects (FOBs): How French tropical tuna purse seiners split fishing effort between GPS-monitored and unmonitored FOBs

Fishing on floating objects (FOBs) dominates catch in tropical tuna purse seine fisheries. One frequently cited advantage of deploying GPS-monitored FOBs is that the position information can be used for directed fishing to reduce search time for tuna. However, purse seiners also fish on foreign objects for which position information is not available. It is critical to quantify the prevalence of fishing on GPS-monitored versus unmonitored FOBS in order to understand how they impact fishing effort and catch per unit effort (CPUE). We analyzed French commercial, observer, and FOB trajectory data in the Atlantic and Indian oceans to determine how often purse seine vessels fish on GPS-monitored FOBs. Only 2.7-20.4% of French FOB fishing sets over 2007-2013 in both oceans were made on GPS-monitored FOBs. Though increasing over time, the low percentage suggests that French vessels do not primarily use GPS-monitored FOBs to reduce search time for tuna. We hypothesize that fishery-wide FOB deployments have important collective consequences for overall fishing effort, and recommend that future effort metrics should be based on fishery-wide FOB activities.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Yearly proportion of vessels of the French purse seine fishing fleet for which information on GPS buoys was available during 2007–2011 in the Atlantic Ocean (AO) and Indian Ocean (IO).

<p>Note that 100% coverage means that 100% of the fishing vessels have provided data but not that they have provided data for the totality of their GPS buoys.</p><p>Yearly proportion of vessels of the French purse seine fishing fleet for which information on GPS buoys was available during 2007–2011 in the Atlantic Ocean (AO) and Indian Ocean (IO).</p

Performance of the classification methods, as a mean of the indicator on the 100 cross-validation iterations for the VEL, MLR, ANN and RF method.

<p>For the MLR, ANN and RF methods, 95% confidence intervals of the difference between the indicator for method and the VEL method are given in square brackets.</p><p>Performance of the classification methods, as a mean of the indicator on the 100 cross-validation iterations for the VEL, MLR, ANN and RF method.</p