Measurements on gill nets in a flume tank

Theoretical study of the effect of round straps on the selectivity in a diamond mesh cod-end

“…Only the meshes a few rows just ahead of the catch accumulation are open and unobstructed during a tow. It is mainly through these meshes that undersized fish escape (Stewart and Robertson, 1985;Wileman et al, 1996).…”

“…The ability of a cod-end to release undersized fish depends on the mesh opening. Underwater observations of diamond mesh codends during trawl fishing have shown that these are distorted into a bulbous shape by water pressure acting on the accumulated catch (Stewart and Robertson, 1985). Most of the netting in front of the bulge is stretched and the mesh opening reduced.…”

Effect of the headline height of gillnets on species selectivity in the Gulf of Maine

“…While the vertical height of a gillnet decreases with increasing current velocity at the depth of the net (Stewart and Ferro, 1985;Stewart, 1988), the reduction may be proportional to the rigged height of the net. Carr et al (1985) measured a gillnet with a 140 mm mesh size, 25 mesh deep in inshore Cape Cod Bay and found the actual headline height before fish were caught was about 1.8 m which was 60% of its rigged height of 3.0 m. Flume tank measurement of gillnet height by Stewart and Ferro (1985), field measurement by Stewart (1988), and theoretical calculation by Matuda (1988) revealed that the height of net is also related to net solidity, twine type, flotation, the direction of net in relation to current, in addition to current velocity.…”

“…Carr et al (1985) measured a gillnet with a 140 mm mesh size, 25 mesh deep in inshore Cape Cod Bay and found the actual headline height before fish were caught was about 1.8 m which was 60% of its rigged height of 3.0 m. Flume tank measurement of gillnet height by Stewart and Ferro (1985), field measurement by Stewart (1988), and theoretical calculation by Matuda (1988) revealed that the height of net is also related to net solidity, twine type, flotation, the direction of net in relation to current, in addition to current velocity. While we did not measure current velocity near the gillnet, its effect on the gillnet headline height may be proportional, i.e., all nets would experience a reduction in height when the current velocity is strong.…”

On the Effect of Water Flow Speed to Hydrodynamic Resistance Force of Gillnet; Model Net Experiments in the Flume Tank

“…Hard sea condition such as fast current of seawater speed could result in the dragging of gillnet or changing the gillnet form (roll over). Water flow speed up to 0.25 m/sec could significantly change the vertical position of the gillnet (Stewart & Ferro, 1985 According to Baranov (1973) & Fridman (1973), gear design, net mesh size and hanging ratio of netting gear were some factors that influence netting gear resistance to hydrodynamic forces. In his theory of geometrical similarity Baranov (1973) stated that the changing of the net mesh size should result in the different size of fish catch.…”