Acoustic assessment of Norwegian spring spawning herring in the wintering area, December 1995 and January 1995
Original version
This report is not to be cited without prior reference to the authorsAbstract
The abundance of the mature component of the stock of Norwegian spring
spawning herring has been estimated based on a series of echo integration
surveys. These were performed in the wintering area of Ofotfjord, Tysfjord,
and Vestfjord in December 1994 and January 1995 using the SIMRAD EK500/38 kHz
echo sounder and Bergen Echo Integrator postprocessing system. Compensation
has been made for extinction, assuming that the ratio of extinction and
backscattering cross sections is 2.41. Three considerations have dictated the
form of stratification of the wintering area: coastline compexity, presence of
herring, and herring size distribution as determined by pelagic trawling. The
variogram has been computed for each stratum to determine the characteristic
scale size of aggregation. Geostatistical theory has been applied to estimate
the variance associated with abundance estimates due to the degree of survey
coverage in relation to observed aggregation properties and fjord geometry.