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.


This study is summarised as evidence for the following.

Action Category

Use acoustic devices on fishing gear

Action Link
Marine and Freshwater Mammal Conservation
  1. 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)

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