Fróðskaparrit - 01.01.1992, Síða 39

TESTING ACOUSTICAL METHODS .. .
43
3 species, as were whistles from the pilots
and the lags.
There is a need for modification of the
acoustic fish: it has to be made insensitive
to low frequency overloading by propeller
noise. Several schemes are possible,
including tuning of the transducers to ultra-
sonic frequencies. This is in part the solu-
tion used in the SONAR.
The primary acoustic detection with the
SONAR of the lags is particularly encour-
aging. It suggests a practical method for
adding an acoustic survey capability at no
cost for ships already equipped with this
instrument. The method can be used both
during dedicated transect cruises as well as
during other activities. If a SONAR is not
installed and an acoustic survey capability
is wanted, an improved version of the
acoustic fish may be worth considering.
Acknowledgements
Dorete Bloch, Føroya Náttúrugripasavn, and Hjalti í
Jákupsstovu, Fiskirannsóknarstovan, were instrumental
in providing ship time. SNF covered travel expenses and
the ongoing development of the acoustic fish through
grant no. 11-7721 to the BioSonar Group.
1987 and NASS-89 data. Rep. int. Whal. Commn
(Special Issue 14).
Møhl, B. 1990. The feasibility of obtaining vital para-
meters by acoustic means. Joumal ofNorth Atlantic
Studies 2(1-2): 77-78.
Thomas, J.A., Fisher, S.R., Ferm, L.M. and Holt, R.S.
1988. Acoustic detection of cetaceans using a towed
array of hydrophones. In: Donovan, G.P. (Ed.). Rep.
int. Whal. Commn (Special Issue 8): 139-149.
Úrtak
Meðan Magnus Heinason var á kann-
ingarferð á Føroya Banka í juni 1992, varð
eitt einfalt lurtitól til at upptaka stuttbylgju-
ljóð (“ a simple, 2-hydrophones, ultrasonic
sensitive detector”) sleipað aftaná skip-
inum. Hetta varð roynt fyri at kanna eftir,
um tólið kundi nýtast til at leita eftir tann-
hvali. Royndin eydnaðist hampiliga væl, tá
ið siglt varð við lítlari ferð. Harafturat vísti
astikið í skipinum seg at vera rættuliga gott
til at leita við, tá ið tað bert varð nýtt sum
móttakari.
Bertel Møhl
Zoophysiology
University of Aarhus
Denmark
References
Adler-Fenchel, H. 1988. Acoustically derived estimate
of the size distribution for a sample of sperm whales
(Physeter catodon) in the Westem North Atlantic.
Can. J. Fish. Aquat. Sci. 37: 2358-2361.
Au, W.W.L. 1988. Detection and recognition models of
dolphin sonar systems. In: Nachtigall, P.E. and
Moore, W.B. (eds.). Animal Sonar. Plenum Press,
N.Y.: 753-768.
Buckland, S.T., Cattanach, K.L., Gunnlaugsson, T.,
Bloch, D., Lens, S. and Sigurjónsson, J. In press.
Abundance and distribution of long-fmned pilot
whales in the North Atlantic, estimated from NASS-