Influence of Different Factors on Abundance Estimates Obtained from Simultaneous Sonar and Echo Sounder Recordings
Journal article, Peer reviewed
Permanent lenke
http://hdl.handle.net/11250/109259Utgivelsesdato
2011-12-28Metadata
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- Articles [3001]
Originalversjon
10.2174/1874252101105010042Sammendrag
Use of horizontal guided sonar in addition to vertical echo sounder may improve biomass estimation of pelagic
fish schooling near the surface. But proportions of horizontal guided sonar to vertical echo integration estimates have been
shown to be very variable, and it is necessary to provide better knowledge on factors that influence acoustic recordings of
fish near surface before a reliable method of combining sonar and echo integration estimates can be established. To
explore factors that influence horizontal sonar recordings of fish biomass near surface, we collected and analysed data
from two acoustic surveys on Norwegian spring-spawning herring (Clupea harengus L.) in the Norwegian Sea in 1997
and 1998, and two acoustic surveys off the southwest coast of Africa, investigating pilchard (Sardinops sagax), anchovy
(Engraulis capensis) and round herring (Etrumeus whiteheadi) off the coast of Namibia in 1994, and sardinella
(Sardinella sp.) off the coast of Angola in 1995. The ratios of fish densities obtained by sonar to those obtained by echo
sounder varied both with respect to location and between different years within a specific location. For three of the four
surveys, the biomass estimated by sonar was significantly higher than the estimates by echo sounder, whereas in the
remaining survey there was no significant difference in estimated biomass. Periods of bad weather, shallow, or lowdensity
patchy fish distributions and mixture of the target species with other species contributed to the higher and more
variable sonar estimates. Still a goal should be to improve knowledge about the factors that contributes to variations
between simultaneously recorded echo sounder and sonar data. An aim should be to combine the recordings from both
methods in the biomass estimations, or at least assess which of the estimates that are less biased under the prevailing
environmental conditions and actual school distribution.