Virginia Institute of Marine Science
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.
CLASSIFICATION; MODELS; BEHAVIOR; SCHOOLS
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The work of DMK and AM was supported by the AMPED project (www.amped.ird.fr) through a grant from the French National Research Agency (ANR, www.agence-nationale-recherche.fr), Systerra Programme, grant number ANR-08-STRA-03. AM also benefited from a grant of France Filiere Peche (www.francefilierepeche.fr). R. J. was financially supported by an ARTS grant from IRD (www.ird.fr) and managed by Campus France (www.campusfrance.org). The fisheries data analysed in this publication were collected by the Mixed Research Unit 212 'Exploited Marine Ecosystems' of the Institut de Recherche pour le Developpement (IRD) through the EU-funded Data Collection Framework [DCF, Reg (EC) 1543/2000 and 199/2008]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
: Maufroy A, Chassot E, Joo R, Kaplan DM (2015) Large-Scale Examination of Spatio-Temporal Patterns of Drifting Fish Aggregating Devices (dFADs) from Tropical Tuna Fisheries of the Indian and Atlantic Oceans. PLoS ONE 10(5): e0128023. doi:10.1371/journal.pone.0128023