Subject: abstract: Hector's dolphins and pingers (fwd)
Mike Williamson (pita@www1.wheelock.edu)
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
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---------- Forwarded message ----------
Date: Fri, 26 Sep 1997 09:22:48 -0400
From: Dagmar Fertl <Dagmar_Fertl@mms.gov>
Reply-To: Marine Mammals Research and Conservation Discussion
<MARMAM@UVVM.UVIC.CA>
To: MARMAM@UVVM.UVIC.CA
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.
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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
3-7.
Stone, G, NEW ENGLAND AQUARIUM, CENT WHARF, BOSTON, MA 02110 USA
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.