The coastal waters off Chiba Prefecture (Fig. 1) are known as a good fishing ground of mackerels by ‘Hanezuri’ (a fishing method by pole line) in spring and in autumn. Two areas neighboring the Tsugaru Straits, i.e. waters off Hachinohe City, Aomori Prefecture, and around the western entrance of the Straits, are also producing a great quantity of mackerels from summer to autumn in recent years. Referring to the 762 daily fishing records in the areas of six boats in 10-20 tons, the writers estimated unit catches (the catch per capita in a boat during a night) and have obtained following results: 1. The mean unit catch in the grand total was 27.8 kan (Table 1). 2. The frequency of unit catches was highest in 15-25 kan. The maximum unit catch was 100 kan (Fig. 2). 3. When mean unit catches of each boat during each fishing season was calculated, the frequency of them was highest in 25-30 kan (Fig. 3). The results show that the mean unit catches of coastal ‘Hanezuri’ boats are exceeding over those by large-sized ‘Hanezuri’ boats (40 and 60 tons), showing 10-20 kan in the East China Sea, off the Goto Islands, and the sea south to Kagoshima Prefecture. Moreover, the unit catches by coastal ‘Tenbinzuri’ (a fishing method by hand line) are far less than those by ‘Hanezuri’ (Fig. 4). Mackerels are divided into four groups by their size in fish markets, but the scale is different according to the localities (Table 2). In recent years, large-sized individuals of Pneumatophorus japonicus (HOUTTUYN), more than about 37 cm. in fork length, have been caught in great quantity around the western entrance of the Tsugaru Straits. At the Hachinohe Fish Market, individuals of 32-34 cm. in fork length are mainly landed. And off Chiba Prefecture, large-sized ones are decreasing in contrast with the notable increase of small individuals of Pneumatophorus tapeinocephalus (BLEEKER) (Fig. 5).
The part seven of this series contains descriptions of life colors of the species nos, 97-111, with some notes on the fishes (several species of Carangidae, Leiognathidae, Oplegnathidae, Mullidae, Cepolidae, and Branchiostegidae) found in Suruga Bay, Japan