New gear handling systems for coastal purse seining.

The paper is describing a new gear handling system for coastal purse seiners. The system consist of a hollow manuverable ring needle through which the purse wire is passing. Solid type rings can be used since the rings will remain on the ring needle or purse wire during the whole operation. The ring bridles are passing an open-topped power block. This system is working very well in combination with the automated net stacking system developed by FTFI during 1976-78. and it is possible to haul and stack the net with only two men and greatly reduce the strain of the work

New gear handling systems for coastal purse seining.

The paper is describing a new gear handling system for coastal purse seiners. The system consist of a hollow manuverable ring needle through which the purse wire is passing. Solid type rings can be used since the rings will remain on the ring needle or purse wire during the whole operation. The ring bridles are passing an open-topped power block. This system is working very well in combination with the automated net stacking system developed by FTFI during 1976-78. and it is possible to haul and stack the net with only two men and greatly reduce the strain of the work

Use of acoustics in studies of fish reaction to imposed stimuli

The general distribution pattern of fish in a large holding pen is described through the integrated echo intensity in six separate cells using transducers mounted below the pen. The reaction of fish to different stimuli, imposed in one of the cells, is quantified by the change in frequency distribution of the echo intensity relative to the undisturbed situation. The experiment was part of a small-scale test of equipment to be used for observations of the attraction-effect of fish to oil-rig structures. The method also seems to be suitable for general fish behaviour studies, particularly concerning attraction and avoidance effects

Survival of mackerel and saithe escaping through sorting grids in purse seines

Technology for efficient size-selection of mackerel and saithe in purse seines has been developed. A critical constraint for application of the technology is the survival of escaping fish. We have conducted a series of mesoscale experitnents where penned fish were forced through rigid grids and into new storing net pens to quantify the survival of mackerel and saithe. These experiments showed insignificant mortality of both mackerel and saithe. Full scale experiments during mackerel purse seining off western Norway and saithe purse seining in fjords in western and northern Norway have also been conducted. During these experiments control groups were established by transferring parts of the catch gently from the purse seine to attached net pens. Experiment groups were established by collecting fish escaping through the selection grids in attached net pens. The net pens were then towed up to 30 nautical miles for anchoring inshore. In the mackerel experiments, up to 95% of the fish in the control groups and up to 60% in the experiment groups were alive one month after the experiments. This indicates that the size selection process in mackerel purse seining induce too high mortality to be recommended in commercial fishing. On the other hand, the mortality in the saithe experiments was insignificant, and the use of size selection grids in saithe purse seines can therefore be recommended

Investigations on diel vertical migration of 0-group fish in the Barents Sea

In August-September diel vertical migration of 0-group fish was studied in the Barents Sea. Redfish and capelin had different vertical migration patterns. 0-group redfish were found at the surface at dark and spread in the upper 50 m during the daylight period while the unpigmented 0-group capelin stayed in small schools close to the surface by daylight and dispersed into a weak scattering layer at the depth of the thermocline (20-30 m) at dark. This behaviour might introduce large errors to the abundance indices of 0-group capelin. Comparative fishing with a pelagic trawl and a purse seine were carried out. The samples showed no significant differences in the length distributions of each species of 0-group fish caught with the two gears