抄録
The numerical estimation of stock capacity in the fishing ground affected by “Gyosho”, which is a kind of artificial reef being use to increase the stock of fish, is supposed to be essential studies on its structure and setting.
For this subject the author tried to analyse the catch data in the fishing ground by the mathematical method originated in its fundamental observations, and a following differential equation on the stock and fishing effort was assumed.
dS/dt=kN(C-S)=fS, df/dt=a-h(C-S)f,
where, C-capacity of “Gyosho”. S-stock remained in “Gyosho”. N-density of population migrated in this ground. f-fishing coefficient. a-the most strong level of the increasing tendency of fishing. others-coefficients.
But, in the state of equilibrium between stock and fishing effort, the coefficient ?? may be shown by the function of catch ??, as follows:
?? ( ?? )=a/hC+ ?? /C,
Furthermore, it was recognized that the point f*, near by ?? showed the vibrating change in relation to catch, therefore, the equilibrium was instability.
Conversely, by the application of moving average for this vibrating change, it was recognized too, that the equilibrium equation approximatelyequalled to ?? ( ?? ) was drawn from ?? ( ?? ) and from this equation the capacity of “Gyosho” was calculated.
By application of this method for the data obtained from Aio Fishing Guild, Yamaguchi Pref., it was supposed the effect was appeared from two to four years after setting.
