dc.contributor.author | Luyeye, Nkosi | |
dc.contributor.author | Coetzee, Janet | |
dc.contributor.author | Boyer, D. | |
dc.contributor.author | Misund, Ole Arve | |
dc.date.accessioned | 2012-10-04T15:55:44Z | |
dc.date.available | 2012-10-04T15:55:44Z | |
dc.date.issued | 1997 | |
dc.identifier.citation | This report is not to be cited without prior reference to the authors | no_NO |
dc.identifier.uri | http://hdl.handle.net/11250/105769 | |
dc.description.abstract | A series of pelagic trawl sampling trials on pelagic species distributed near surface off Angola
were conducted by R/V «Dr. Fridtjof Nansen» operating a medium sized pelagic trawl with a
vertical opening of about 20 m. The results have been analysed with respect to effects such as
vessel and gear avoidance, time of day, towing speed and tow duration. Numerous trawls
targeting on dense sardinella shoals failed to yield large catches. Shoals that were at the trawl
depth as the vessel passed over were often observed far below the foot rope of the trawl,
indicating vertical avoidance. Often shoals in the net mouth were recorded by the net sonde
for long periods. It was assumed that these fast swimming fish were able to swim along with
the trawl, and escaped out of the trawl when slowing down the towing speed during hauling.
No correlations were, however, found between towing speed in the range 2.7 - 5.0 knots and
the total catch of sardinella. Increasing the tow duration during the day to more than 120
minutes also failed to yield consistently higher catches. At night, there was a negative
correlation between tow duration in the range 15 - 60 min and the catch size, simply because
the trawl was towed for a longer time to obtain proper samples in areas with scattered
recordings. During the day sardinella was caught both inshore and further offshore, while
horse mackerel was caught further offshore only. Both species were well represented in the
catches made at night. There were substantial day and night differences in the length distributions of sardinella with small sardinella being caught only at night. | no_NO |
dc.language.iso | eng | no_NO |
dc.publisher | ICES | no_NO |
dc.relation.ispartofseries | ICES CM Documents;1997/W:12 | |
dc.subject | trawl | no_NO |
dc.subject | trål | no_NO |
dc.subject | pelagic fish | no_NO |
dc.subject | pelagisk fisk | no_NO |
dc.subject | sampling | no_NO |
dc.subject | prøvetaking | no_NO |
dc.subject | stock assessment | no_NO |
dc.subject | bestandsberegning | no_NO |
dc.title | Trawl sampling of small pelagic species off Angola. Effects of avoidance, towing speed, tow duration and time of day | no_NO |
dc.type | Working paper | no_NO |
dc.subject.nsi | VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Catch: 925 | no_NO |
dc.subject.nsi | VDP::Mathematics and natural science: 400::Geosciences: 450::Oceanography: 452 | no_NO |
dc.subject.nsi | VDP::Agriculture and fishery disciplines: 900::Fisheries science: 920::Fish health: 923 | no_NO |
dc.source.pagenumber | 18 s. | no_NO |