Distribution of catch per unit of effort does not fit in Poisson distribution premised the independent action of individual, because many fishes seem to form their shoals respectively.
But, it is asumed that the shoal constructed with individuals of fish will fluctuate itself and we are able to estimate that the distribution of number of shoal in some limited area will fit in Poisson distribution.
If the distribution of appearable probabilities of shoal is shown as fn (m), the probability of number of fish W (n) in some limited area will be expressed as W(n)=nΣm?1exp(-μ)•μm/m!•fn(m)…… proviso; m denote number of shoal, n denote number of fish in limited area and μ denote average number of shoal.
Therefore, fn (m) will be able to calculate from the counted number W (n) in fishing.
As the result, the distribution of fn (m) in each market size of Kidai, Taius tumi frons, is shown as Fig. 3 and the elementary connection of individuals in shoal of Kidai of small and middle market size is estimated as 4r, (r=0, 1, 2, 3, ……) but in large sie their connection is unknown.