Fishing and Gear Technology

Unit 10- Maintenance and storage of gears

10.6. Basic principles of Fishing Gear Design and Construction
Fishing gears evolved on a trial and error basis and until recently, only empirical approaches have been used to determine design paramteres rather than analytical procedures. Design and development efforts based on fish behaviour, engineering studies, system analysis and model studies taking into consideration resource conservation, ecological and economics issues have been taking place in the recent decades. With the development and wider availability of synthetic gear materials, recent advances in vessel technology, navigational electronics, gear handling machinery, fish detection methods and fish behaviour studies, large-scale changes have taken place in the design, fabrication, operation and catching capacity of modern fishing gears such as trawls, purse seines and long lines. Widely used traditional fishing gears such as entangling nets, hook and lines and traps have also benefited by way of design upgradation and efficiency improvement in the recent years.
Choice of fishing gear and its design primarily depends on biological, behavioural and distribution characteristics of the target species. There is no universal fishing suitable for all fishing conditions and resources. Fishing gear has to be selected or designed based on the presence of maximum number of attributes suitable for the particular fishing condition and resource and trade-offs may be necessary. Principal mechanisms used in fish capture are (i) filtering e.g. trawls, seines, traps; (ii) Tangling e.g. gill nets, entangling nets, trammel nets; (iii) Hooking, e.g. hand line, long line, jigging; (iv) Trapping, e.g. pots, pound nets; (v) pumping, e.g. fish pumps. Main behaviour controls used in the fish capture process are (i) attraction, e.g. bait, light, shelter; (ii) repulsion or avoidance reaction, e.g. herding or guiding by netting panels as in set nets and trawls or sweeps and wires as in boat seines and trawls.
Model testing is increasingly used for design evaluation of the existing commercial fishing gear designs with a view to optimize their design parameters and for development of newer designs. In model testing, a scaled down model of the fishing gear is tested in a flume tank in order to study its behaviour and estimate working parameters. Principles of similarity are then used to assess the dimensions, specifications and characteristics of the full-scale version based on model studies. The fishing gears are further evaluated using full-scale version through statistically designed comparative field trials with a gear of known fishing efficiency and operational parameters are verified through gear monitoring instrumentation and underwater observations.