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

Published source details Tixier P., Gasco N., Duhamel G. & Guinet C. (2015) Habituation to an acoustic harassment device (AHD) by killer whales depredating demersal longlines. ICES Journal of Marine Science, 72, 1673-1681.
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This study is summarised as evidence for the following.

	Action	Category
	Use acoustic devices on fishing vessels Action Link

Use acoustic devices on fishing vessels

A controlled study in 2011 of a pelagic area in the southern Indian Ocean off the Crozet Islands (Tixier et al. 2015) found that when an acoustic device was turned on during fishing hauls, killer whales Orcinus orca were recorded further from the fishing vessel than when the device was turned off, but distances decreased after the first exposure to the device. Killer whales of two family groups were recorded at greater distances from the fishing vessel during hauls when an acoustic device was turned on for the first time (average 933 m) compared to when it was turned off (average 277 m). Average distances to the vessel decreased significantly during successive exposures to the acoustic device for both groups (first exposure: 800–1,000 m; after 5–22 exposures: 90–240 m). In February 2011, a fishing vessel targeting Patagonian toothfish Dissostichus elegenoides deployed an acoustic device (comprising 40 transducers placed 8–10 m below the vessel) during hauls of 23 ‘long lines’ (each 5.4 km long with 4,500 hooks) with killer whales present. During 15–20-minute intervals, the device was alternately turned off (silent; total 31 intervals) or on (emitting 0.5–1 second sounds at 6.5 kHz; total 45 intervals). An onboard observer recorded the distance of killer whales from the vessel. Individuals within two family groups were identified from photographs.

(Summarised by: Anna Berthinussen)