Abstract
Since the inception of the 20th century, the sardine catch in the Far East has fluctuated remarkably. The author has analysed the mechanisms underlying the fluctuation as well as biological information needed for the study.
1. Following is a summary on the biological information pertinent to the study of the fluctuation in the sardine population.
a. The investigation of literature and published data revealed that almost all the sardine catch in the Far East has been composed of a single species, Japanese sardine, Sardinops melanosticta (TEMMINCK & SCHLEGEL)
b. The Japanese sardine has been widely distributed in the coastal waters along the Japanese Islands. The distribution range and migratory routes have changed according to fluctuation in the population size.
c. The Japanese sardine mainly spawn in the waters south of the central part of Japan during winter and spring. The spawning ground also indicated a large scale shift depending upon the population size.
d. It has been estimated that almost all the sardine eggs are fertilized just after they were discharged in the sea. The development changes depending upon the temperature, along the ARRHENIUS's equation with the coefficient of μ of about 31, 000. The mortality rate at the early stage, around time of the absorp tion of yolk, is very high, only 0.1 percent of fertilized eggs may survive at a postlarval stage of 15 mm in total length.
e. Most of the distinct scale rings are annuli that form during winter and early spring. The growth rate of the fish increases in the spring and decreases in winter. The growth of the fish throughout their life span fits to BERTALANFFY's equation. An example of the growth curves is calculated on the basis of data taken during 1949 through 1951 as follows:
l=22.39 {1-e-0.87 (t-0.0483) } cm.
f. The study on fecundity of the sardine is less conclusive. It is estimated that a female ovulates 24, 000-48, 000 ova at one spawning activity and that many fish spawn two or more times in a season.
g. Postlarvae just after absorption of yolk feed mainly on copepodan eggs and nauplius. After that stage, the sardine eat zooplankton and phytoplankton in situ.
h. Major gear to catch the sardine are round hauls, drift nets, set nets, lift nets, and boat and beach seines. The fishing season differs depending upon the locality of fishing ground, and the size and the age of fish to be caught. A remarkable fluctuation has been observed in the geographical locations of the major fishing grounds.
2. The sardine was fished since the ancient years. There are records indicating that the fluctuations in the sardine catch caused prosperity and collapse of some fishing villages. The following outstanding phenomena were observed since the research systems on the catch and biological backgrounds of the sardine were established in the inception of the 20th century.
a. The annual sardine catch in the Far East was less than 150, 000 tons before 1910, increased rapidly since around 1924, and exceeded 2, 000, 000 tons around 1935. The catch was on the tremendous decrease in the 1940's, until it dropped to merely 160, 000 tons in 1945. Since then the sardine landings recovered slightly, being between 300, 000 and 500, 000 tons up to 1953, but decreased again in 1955 to around 200, 000 tons. In the prosperous period around 1935, the major portion of the sardine catch were obtained on the Pacific coast of northeastern Honshu and Hokkaido, and the Japan Sea coast of North Korea. Sardine were also caught then in the waters adjacent to Coast Range and Sakhalin. After 1945, no commercial fishery was present on the North Korea, Coast Range and Sakhalin. Around 1950 the waters northwest of Kyûshû were the most im portant fishing grounds of the sardine, and, since around 1955, the major catch has been brought from the waters around the Noto Pe
