Subject: abstract: Hector's dolphins and pingers (fwd)

Mike Williamson (
Fri, 26 Sep 1997 19:30:43 -0400 (EDT)

"Follow in my wake, you've not that much at stake,
For I have plowed the seas, and smoothed the troubled waters"
                        Jimmy Buffett

---------- Forwarded message ----------
Date: Fri, 26 Sep 1997 09:22:48 -0400
From: Dagmar Fertl <>
Reply-To: Marine Mammals Research and Conservation Discussion
Subject: abstract: Hector's dolphins and pingers

     Close on the heels of the postings about pingers reducing harbor
     porpoise mortality, the following might be of interest to folks
     following this issue.


     Stone, G; Kraus, S; Hutt, A; Martin, S; Yoshinaga, A; Joy, L.  1997.
     Reducing by-catch: Can acoustic pingers keep Hector's dolphins out of
     fishing nets? MARINE TECHNOLOGY SOCIETY JOURNAL, Summer 1997 v31 i2 pp


     Underwater acoustic pingers, emitting a 10 kHz sound (with harmonics
     up to 110 kHz), were tested in New Zealand to evaluate their
     potential effectiveness in preventing entanglement and death of
     Hector's dolphins (Cephalorhynchus hectori) in gillnets. A 1996 study
     site was established in Akaroa Harbour, an area known for high
     concentrations of Hector's dolphins. A remote controlled device was
     installed which would raise and lower either active or passive
     acoustic pingers via a radio link from shore. Observations of dolphin
     movement and distribution were made from a land-based station using a
     theodolite and logged directly into a computer. Observers did
     not know if the pinger in the water was active or passive. This
     ''blind'' experiment was designed to measure the spatial difference in
     dolphin distributions between active or passive pinger use. Two data
     subsets were used in the analysis, representing the distance
     between sighted dolphins and an active pinger and the distance between
     sighted dolphins and a passive pinger. The distribution of the
     distance data was significantly non-normal (p<0.001), so the
     non-parametric Mann-Whitney rank sum test was used to compare
     dolphin distributions from the two subsets. In this analysis, all
     sightings data were included; the median distance value for the
     passive pinger trials was 299m (n=492) and the median distance value
     for the active or insonified trials was 372m (n=552). Results indicate
     that Hector's dolphin distributions were affected by the 10 kHz
     pingers and that dolphins avoided the immediate area where the pingers
     were active, but did not avoid the larger area of Akaroa Harbour. All
     dolphin sightings made during active pinger trials were distributed
     significantly farther from the sound source (p<0.001) than were
     sightings during passive trials.