Identification of static netters fishing trajectories with high resolution data and their evolution in the Bay of Biscay since 2015: Potential implications for short-beaked common dolphin bycatch

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Since winter 2016, an increase in strandings of small cetaceans has been recorded along the French Atlantic seaboard. This mortality, which concerns mostly the short-beaked common dolphin (Delphinus delphis), is mainly due to bycatch in fishing gears. Highly vulnerable towards this issue, this protected species is more and more threatened in the Bay of Biscay. Fine scale knowledge on fisheries practices, which are ever evolving, is paramount to address the bycatch issue. The objective of this study was to identify the individual trajectories of static netters flying the French flag and to highlight possible changes in their practices between 2015 and 2019, during the winter period. An analysis of AIS data from vessels over 15 m of length, using a clustering method (HCPC), enabled us to define a typology of the static net fishery trajectories. The possible main trajectories of static netters flying the French flag were identified. Among these, one trajectory was linear with a constant navigation path and was used by offshore gillnetters targeting hake. This trajectory increased in frequency between 2015 and 2017. This study improves knowledge on practices of passive fishing gears that present a risk of short-beaked common dolphin bycatch such as gillnets and trammel nets in the Bay of Biscay. Further analysis of AIS data from other years and fishing fleets, adding environmental data or even dolphin distribution, are needed for a full understanding of the bycatch issue and towards the implementation of efficient mitigation measures.