The following is an abstract from the latest issue of Aquatic Mammals;
it is posted as a courtesy to the European Association for Aquatic
Mammals and the journal editor, Dr. Jeanette Thomas. Aquatic Mammals is
the scientific, peer-reviewed journal of the European Association for
Aquatic Mammals (EAAM). More information on the EAAM, society membership,
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journal-related inquiries may be directed
to the journal editor:
Dr. Jeanette A. Thomas
Laboratory of Sensory Biology
Western Illinois University-Quad Cities
3561 60th Street
Moline, IL 61265, USA
Phone +1 309 762 9481, ext. 262
Fax +1 309 762 6989
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Mooney, T.A.*, P.E. Nachtigall, and W.W.L. Au. 2004. Target strength of a
nylon monofilament and an acoustically enhanced gillnet: Predictions of
biosonar detection ranges. _Aquatic Mammals_ 30(2):220-226.
*Hawaii Institute of Marine Biology, University of Hawaii, P.O. Box 1106,
Kailua, Hawaii 96734, USA
Thousands of marine mammals die each year in fisheries-related
entanglements. A substantial number of these animals entangle themselves in
gillnets. Two populations in immediate danger are the coastal stock of the
mid-Atlantic bottle-nose dolphin, _Tursiops truncatus_, and the Gulf of
Maine harbour porpoise, _Phocoena phocoena_. We investigated the efficacy of
using an alternative net material made with barium sulphate hypothesized to
be acoustically more reflective than traditional nets. By using simulated
dolphin echolocation clicks, the target strength of the experimental net was
compared with the target strength of a similar gauge nylon net. Results
demonstrated that at angles greater than normal incidence, but less than
40°, the new barium sulphate net was acoustically more reflective than the
nylon net; however, there was no significant difference in the target
strength of the two nets at 0°. At angles greater than 40°, both nets were
difficult to discern from background noise. Target strengths of the nets
were used to calculate detection ranges for _T. truncatus_ and _P.
phocoena_. Both species should be able to detect the experimental nets at a
distance greater than the nylon nets. For _T. truncatus_, this distance may
be enough to reduce entanglement; however, because of _P. phocoena's_ lower
source level echo-location signals, they may not detect either net with
echolocation in time to avoid contact.
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