Short term variability in the Tsugaru warm current and its effect on fisheries

Abstract

A study on the short term variability of the ocean and its effects on the distribution of fish shoals in the coastal area of NE Japan has been conducted. The efforts have been made to detect the temporal changes of the Tsugaru Warm Current in summer and autumn (i.e. fishing seasons) by using the satellite infrared images (NOAA7-9) and concurrent hydrographic observation data. Also fish shoal (mackerel and sardine) distribution was investigated by echo-sounder and fishing fleets' operation data. The satellite images revealed that the gyre of the Tsugaru Warm Current changed entirely in a short time, and sometimes the gyre was devided into two parts. The time scale of this process was estimated to be 1–2 weeks. Corresponding to this process, the fishing grounds changed rapidly. A part of the Tsugaru Warm Current flows from the gyre southward along the coast. The flow has a temperature front against the Oyasio water intrusion, showing a wave-like perturbation propagating to the S. At the perturbed frontal area, Mackerel fishing grounds formed frequently. The fish shoals distributed in the warmer side of this frontal zone. By revealing the mechanism of the characteristic variability, the movement of fishing rounds may be predicted.