A method to reduce survey bottom trawl variability
Working paper
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http://hdl.handle.net/11250/104856Utgivelsesdato
1991Metadata
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This report is not to be cited without prior reference to the authorsSammendrag
A technique for limiting the variability of trawl doorspread is described. In addition,
modifications of trawling technique which enable the doors to stay upright and maintain
constant ground contact under different trawling conditions are presented. Observations were conducted using a standard Campelen 1800 otter trawl in 270 m of water. Doorspread was
restricted by means of a restraining rope mounted between the warps, 150 m in front of the
doors. When the restraining rope was in place, doorspread varied little and was not influenced
by warp length; the doorspread was approximately 51 m for warp lengths of 600 to 800 m.
With the restraining rope removed, doorspread increased from 54 to 63 m as warp length was
increased over the same range. It was also demonstrated that doors would stay upright and
maintain the same ground contact under varying conditions, if warp length was adjusted
correctly according to depth. This was based on a requirement that warp tension and elevation
angle be adjusted so that 2/3 of the door weight in water is counteracted by the upward pull
of the warp at the end nearest the door.