Horizontal distributions of demersal fishes are discussed from catch data of coastal set-line (Tama-nawa) operations, conducted at Sagami Bay during 1979-1981. For Analytical procedure, occurrence proportions of catch in branch lines are taken into consideration, which indicate the spatial distributions of catch among branch lines.
Here, a branch line is considered as a unit gear, which consists of five hooks arranged vertically. Assuming that the probability of catch per book (P) is constant in each hook used in a operation of a set of Tama-nawa gear, occurrence proportion of catch in branch lines (Pc) is expected as, Pc=1-(1-p)3 Meanwhile, actual observations on occurrence proportion of catch in branches (P) are obtained by P=B/Bo, where Bo denotes total nomber of branch lines used in the operation and B is the number of the catch-occurred branches. In comparison between the observed proportion (P) and the expected proportion (Pc) of catch occurrencein branches, uniformity or contagiousness of catch among branches is discussed on total catch, and further, on seven species of the main catch.