NOAA Technical Memorandum
NMFS-AFSC-84
Observations of harbor porpoise in the vicinity of acoustic alarms on a set gill net
Abstract
Large and small-scale fishery experiments have demonstrated that attaching acoustic devices (pingers) on gill nets reduces harbor porpoise (Phocoena phocoena) entanglement and mortality. However, the mechanism for mortality reduction is unknown. We conducted shorebased observations of a set gill net that was alternately set with and without alarms for 2- to 5-day periods during 27 days between 11 July - 6 August 1996. When the acoustic alarms were attached to the net, harbor porpoise were displaced by an acoustic buffer with a radius of at least 125 m around the net (P <0.01), which demonstrated the effectiveness of pingers in reducing entanglement.
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