FEATURES OF FISH BEHAVIOR IN THE ACTION ZONE OF MIDWATER TRAWL

Researches in the field of behavior and distribution of fish at different stages of fishing were conducted using midwater trawls in order to increase fishing efficiency, subject to the fact that, besides fish behavior, parameters of midwater trawls and types of trawling affect the efficiency of trawling. Congestions of catch objects at midwater trawling have been described. Evaluating the behavior reactions of fish under natural conditions was investigated accounting the nature and density of fish schools, their manner of migration and the depth of location. The behavior pattern of an object of catch in the acoustic and hydrodynamic areas of the vessel has been specified. Despite insignificant impact of fields of the tackle in the front part of a trawl on fish, the directing and restrictive action of fields due to the big volume of this part of the trawl is enough to prevent fish escaping from the fishing gear, which could increase catch efficiency. There have been described the conditions for decreasing fish escape from fine mashed and wide meshed parts of the trawl. It was shown that to regulate the fish behavior in the fine mashed part of the trawl and to obtain maximum efficiency of fishing, it is important to trawl with average speed. Catch efficiency is linked to fish behavior in the trawl bag and depends generally on its selective properties and parameters that determine selectivity (operating size of a mash, relative mash extension, biometric parameters of fish body, size and species composition of schools, intensity of fish entering the trawl bag, catch amount). In the course of the research there have been specified the empirical dependences describing parameters of movement of fish schools under the external conditions.