Acoustic abundance estimation of wintering Norwegian spring spawning herring, with emphasis on methodological aspects
Working paper
Permanent lenke
http://hdl.handle.net/11250/105253Utgivelsesdato
1994Metadata
Vis full innførselSamlinger
Originalversjon
This report is not to be cited without prior reference to the authorsSammendrag
The spawning component and part of the juvenile stock of Norwegian spring spawning
herring have been wintering in a fjord system in northern Norway in recent years.
Conditions for measuring the stock size have been excellent. Here, results are presented
from the December 1993 and January 1994 cruises with RIV "Johan Hjort", supplemented
by measurements with RIV "Michael Sars" in December 1993. Following a review of the
biology, principal elements of the survey are described, namely design, acoustic
measurements, and biological sampling. A variety of auxiliary studies, some ongoing, are
breifly reviewed. The subjects of these are ( 1) acoustic extinction, (2) fish orientation in
situ, (3) fish target strength in situ, ( 4) geographic differences in size distribution and
associated dynamics, ( 5) herring fat content, ( 6) hydrography with respect to herring
distribution, (7) inter-ship calibration of echo integrators, and (8) multi-frequency echo
integration. Methods of analysis: criteria for echogram interpretation, stratification, global
averaging, and geostatistical estimation of variance, are described. Results of the acoustic
survey are expressed through absolute numbers for abundance, composite size distribution,
and estimates of confidence associated with the degree of coverage based on geostatistics.
The results are placed in the context of other methods of assessment and prognoses. Error
sources in the acoustic abundance estimate are enumerated and critiqued. Outstanding
problems, if obvious, are mentioned.