Acoustic harassment devices reduce seal interaction in the Baltic salmon-trap, net fishery

Published source details Fjälling A., Wahlberg M. & Westerberg H. (2006) Acoustic harassment devices reduce seal interaction in the Baltic salmon-trap, net fishery. ICES Journal of Marine Science, 63, 1751-1758.
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This study is summarised as evidence for the following.

	Action	Category
	Use acoustic devices on fishing gear Action Link

Use acoustic devices on fishing gear

A replicated, controlled study in 1998–2000 at 19 pelagic sites in the northern Baltic Sea, Sweden (Fjälling et al. 2006) found that using acoustic devices at salmon trap-nets resulted in an increase in intact fish catches and a decrease in damaged fish and fishing gear, likely due to reduced grey seal Halichoerus grypus predation. Trap-nets with acoustic devices had higher intact fish catches (26 kg/day), lower average quantities of fish damaged by seals and birds (4 kg/day) and fewer new holes in fishing gear (result reported from text, which does not match data in table) than those without acoustic devices (fish catches: 12 kg/day; damaged fish: 7 kg/day). Salmon trap-nets were deployed at each of 19 sites (3–9/year) with acoustic devices (total 600 fishing days, 755 trap-net lifts) and without acoustic devices (total 493 fishing days, 668 trap-net lifts). Trap-nets consisted of a leader net starting close to the shore and ending in a funnel-shaped net and fish chamber (10 x 5 x 5 m). An acoustic device (Lofitech Fishguard) was deployed on a raft next to the fish chamber with the transducer at a 5 m depth (emitting 250–500 ms pulses at 15 kHz). Eight commercial fishers recorded catch weight, numbers of fish damaged by seals and birds, and damage to fishing gear during a total of 1,423 trap-net lifts across three fishing seasons in 1998–2000.

(Summarised by: Anna Berthinussen)