Mackerel fishing by ‘hanezuri’* has been carried out by fishermen in the coastal waters off Hachinohe, Aomori Prefecture, since the first trial by the research boat “Chiba-maru” (36.78 ton), Chiba Prefectural Fisheries Experiment Station, in the summer, 1951.
During July 24-August 2, 1955, the Chiba-maru tried the ‘hanezuri’ off Hachinohe, and in adjacent southerly waters off northern Iwate Prefecture (Fig.1). The present writers were on board in the cruise, and examined the fishing ground, migration and the food of the mackerel, obtaining following results: -
1. Mackerel fishing by ‘hanezuri’ was successfully possible in the sea off northern Iwate Pref. in the summer, 1955 (Table 1). The surface water temperature in the fishing ground was 19.8-22.0°C, and coastal currents were flowing to south. The mackerel schools were consisted of
Pneumatophorus japonicus (HOUTTUYN) only, and the folk length of individuals was more or less 30cm. Gonads were all immature. The fishing stations were sometimes indicated well by flocks of sea birds on the surface of the sea.
2. The migration was studied by tagging method. 332 individuals were tagged during the expedition. Among them 5 individuals were caught by trap-nets on the coast of southern Iwate Pref. They migrated to 110km south in 15-23 days (Table 2).
3. The food of the mackerel taken of Kuji, in northern Iwate Pref., was mainly composed of following animals:
Engraulis japonica TEMM. & SCHL.,
Euphausia pacifica HANSEN and
Calanus plumchrus MARUKAWA.
The predominating constituent was not similar qualitatively in ten stomachs obtained around a station in the same time (Table 3). This may be caused by considerably irregular distribution of the populations of each food animal in the coastal water.
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