On the Oceanographic Condition for Albacore in the Western South Pacific Ocean

Abstract

The western sea area of the Fiji Islands is known as having an abundance of large-sized albacore. Tuna fishing and oceanographic observations were performed in this area by the training ship “Hokusei Maru” of Hokkaido University, during the period of November from 1964 to 1968. The results of these observations revealed the following:
1) The isotherms and isohalines extended from west to east depicting waves from south to north. According to dynamic topography, the water mass in this area was flowing from west to east.
2) Saline water, having a peak of about 35.7‰ at the 200m level, projected to the south and the sea temperature showed a sudden drop at it's south side.
3) T-S curve showed variations below the 300m level by difference of horizontal positions, but over the 300m level described an almost regular curve.
4) Hook rate of albacore was 2.05-3.25% every year.
5) Maximum hooked rate of albacore was obtained at 200-260m depth in tuna long-line.
Putting these results together, we found a sea structure composed of a discontinuity of temperature and salinity, and suppose that dynamically liquidity is happened around the water mass of high salinity to project at the 200m level.
Probably this sea structure of discontinuity is closely connected with the formation of the fishing grounds for albacore.