Substantiation of the gears for salmon fishery alternative to gill nets
Wing nets and hook lines are the main gears used for salmon fishery in the period of salmons migration. They were tested comparatively, with taking into account the birds mortality. Optimal sizes of nets, their wings and mouths, mesh size were determined, methods of the nets shaping for better catchability were proposed. Compact traps with flexible frame were suggested as an effective gear for salmon fishery. Catch abilities of the gears were measured quantitatively with using the specific catch value - the catch provided by each linear meter of a gear. The wing nets were characterized by the specific catch 0.26-0.60 sp./m depended on fishing grounds (Primorye, Kuriles, Kamchatka), and the hook line - by the specific catch 0.25 sp./m (0.38 sp./hook), so these two gears had a comparable catch ability. Size (average, modal, and maximal length) of salmons caught by both gears was almost the same. The hook line was better for fishery at night when its catches were higher than the catch in the evening in 1.92 times for chum salmon and in 1.65 times for pink salmon. On the contrary, its by-catch of birds, squids and other fish species was lower at night - 57 % of the evening by-catch. The compact traps had a considerable by-catch in coastal waters, including walleye pollock, yellow perch, saffron cod, herring, and greenlings. To avoid the by-catch, long cylindrical and conical traps are recommended equipped with flexible frame and several entries.