Near-bottom sampling with bottom and pelagic trawls
Working paper
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http://hdl.handle.net/11250/104260Utgivelsesdato
1987Metadata
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This report is not to be cited without prior reference to the authorsSammendrag
The Institute of Marine Research, Bergen, has carried out
combined bottom trawl and acoustic surveys for cod and haddock
in the Barents Sea - Svalbard area since 1981. These investigations
have demonstrated clearly that the currently applied survey
methods considerably underestimate the young age groups of cod.
For haddock the survey abundance estimates have been considerably
higher than those used in the stock assessment. Part of the
problem has been shown to be be low bottom trawl efficiency for
small fish. It has also been indicated that the pelagic trawl
has low efficiency for cod.
In this paper variation in length and species composition from
samples taken with a bottom trawl and with a pelagic trawl on and
off bottom are analyzed. Differences in sampling efficiency and
the problems connected with combining data from different trawls
during routine surveys are discussed.