ベーリング海におけるフィッシュミール船団所属以東底曳船の,1日当り揚網回数の季節変化と昼間の長さとの関係

Abstract

The tendency of the boats not to fish actively or to take recess at night and the large variation of the length of daytime during long season at high tatitudal waters suggested the possibility of the number of daily hauls depending on the length of daytime. In confirmation of this possibility, the daily reports by the 22 Danish seiners of one of the fish-meal fleets in the Bering Sea during the entire season in 1963 were analyzed here, too. And the results obtained are summarized as follows: 1. The number of daily hauls per boat showed a general tendency of increase with elongation of daytime, although fluctuated severely from boat to boat and day to day even within successive 10 days. 2. Analysis after stratification according to the area revealed the following tendencies: The number of daily hauls changed closely depending on the length of daytime during the season in which the boats operated in Area A and Area B, but this was kept at a stable level of about seven hauls a boat regardless of the length of daytime during the season in Area C. 3. The presence of a close relation of the number of daily hauls to either the depth of fishing ground or the daily catch was found in the previous reports. Reasonable attention should, therefore, be paid to the close relation of the depth of fishing ground or the daily catch to progress of the season. This made it hard to isolate the dependence of the number of daily hauls per boat on the length of daytime from that on the other factors.