長崎縣五島西村及び伊豆網代赤石崎に於けるブリ網の漁況に就いて

抄録

The present paper is based on the daily records of the catch of the keddle nets (1) in the Nisimura fishing ground of Gotô in Nagasaki Prefecture and (2) in the Akaisizaki fishing ground on the east coast of Idu Peninsula. The former covers nine fishing seasons of “Buri” (Seriola quinqueradiata T. & S.) 1918 to 1926 inclusive, and the latter six seasons of the same, 1927 to 1932 inclusive.
The catches from the above mentioned two fishing areas consist of “Buri, ” “Iwasi” (Amblygaster melanosticta T. & S.), “Saba” (Scomber japonicus Houttuyn), “Maguro” (Thynnus thynnus (L.)), “Tobiuwo” (Cypsilurus agoo T. & S.) and “Sawara” (Scomberomus niphonius Cuvier and Valenciennes). In the present study, especial reference has been given to the analysis of fluctuation in the catch of “Buri, ” with the following results: -
(1) The size of the yearly catch of “Buri” in the Nisimura fishing ground is significantly correlated with the number of the catches of 1, 000 individuals and over a day (r=+0.82).
(2) The size of the yearly catch is mostly determined by the size of stock of the predominant year class which again depends on the conditions of life during the period of hatching which took place 4-6 years before the fishing. As to “Buri” fished on the Nisimura ground, a very large stock of it is obtained when the meteorological and hydrographical conditions are moderate (Fig. 3).
(3) The correlation between the time of first catch and the average water temperature in January is negligibly low (r=-0.16), and that between the time of the last catch and the average water temperature in March and April is not so high (r=+0.13 and r=+0.45). But the duration of the fishing period between the first and the last catches is longer than usual when the average water temperature in March is lower than that in January (r=+0.65), and when the rising of water temperature is slower than that in average year (Fig. 4).
(4) If the duration of the fishing season of “Buri” is represented by T days, the number of daily catches of “Buri” in T days by n', that of any other fishes by n" and the number of coincidences of both daily catches by p, then the probability of existence of any cause from which the catch of “Buri” is resulted to occur in coin cidence with (or against to) the catch of the other fish in question is numerically represented by the magnitude of the difference of P/T/(n'/T×n"/T) from 1. The data from the Akaisizaki fishing ground give that P/T/(n'/T×n"/T) is 1.0-1.3 for “Iwasi, ” 0.6-1.3 for “Maguro” and 0.5-1.0 for “Saba.”