Fishing and Gear Technology

Unit 10-Maintenance and storage of gears

10.7.Factors affecting fishing gear design

10.7.2.Fishing depth, current and visibility
Hydro-acoustic pressure increases approximately at the rate of one unit atmospheric pressure (1 bar) for every 10m depth. Buoyancy elements used in the deep sea fishing gears such as deep-sea trawls, gillnets and bottom vertical lines have to be strong enough to withstand the high pressure at the fishing depth. Compressible buoyancy elements that are simple light and cheap can only be used in surface operated gears such as seines and surface gillnets as they absorb water and loose their buoyancy in deeper waters.
Prevailing strong currents in the fishing ground may restrict the choice of fishing gears to longlines and gillnets which are less affected by currents. Light levels at the fishing depth could influence the fishing success, as vision of fish is affected by light levels. In passive fishing gears such as gillnets, visibility of netting panel adversely affects fishing efficiency. Negative impact of visibility is observed in hook and line operation while in light-assisted jigging controlled lighting has a positive impact. Visibility is also important in effective herding during the capture process in trawls and in large pound nets and trapping enclosures where leader nets are used.