Habituation to an acoustic harassment device (AHD) by killer whales depredating demersal longlines

• Published in: ICES Journal of Marine Science
• Main Authors: Tixier, P., Gasco, N., Duhamel, Guy, Guinet, Christophe
• Other Authors: Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), Institut National de la Recherche Agronomique (INRA)-La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), Département Milieux et Peuplements Aquatiques, Muséum national d'Histoire naturelle (MNHN)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: acoustic harassment device AHD; depredation; killer whales; longline fisheries; [SDE]Environmental Sciences; Crozet Islands
• Online Access: https://hal.science/hal-01060230; https://doi.org/10.1093/icesjms/fsu166

International audience Acoustic harassment devices (AHDs) have been increasingly implemented in various fisheries that suffer significant losses caused by odontocetedepredation. However, the efficacy of AHDs to deter odontocetes from fishing gear remains poorly investigated. To determine the effectiveness ofAHDsin deterring depredation,weexperimentally tested a high amplitude device (195 dB re 1 mPa 6.5 kHz 1 mfrom the source) froma Patagoniantoothfish Dissostichus elegenoides longliner operating off the Crozet Islands, while it was subjected to heavy depredation by killer whales Orcinusorca. This species usually depredates longlines within a 10- to 300-m range from the vessel, as they only have access to fishing gear during hauling.Weexpected this distance to increase in response to the acoustic disturbance created by the AHD. The distances of 29 killer whales from the vessel(n ¼ 1812 records) were collected during phases of AHD activation and phases during which the AHD was turned off. Two multiexposed killerwhale social units fled over 700 m away from the vessel when first exposed to the AHD. However, they remained within a 10- to 300-m rangeand depredated longlines again past the third and seventh exposures, respectively, showing an insignificant behavioural response to further activationsof the AHD. When tested through generalized linear mixed models, the effect of AHD activation was only significant when killer whales werefirst exposed to the device. However, the effect disappeared after successive exposures suggesting that killer whales became habituated to the AHDand may sustain potentially harmful hearing disturbance to access the resource made available by longliners. In addition to raising significant conservationconcerns, this rapid return of initial depredation behaviour strongly suggests that AHDs are ineffective at deterring depredating killerwhales, and that fisheries should favour the use of other mitigation techniques when facing repeated depredation by this species.