Horizontal Distribution of Catch among Branches in Coastal Set-line

Abstract

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 (P_c) is expected as, P_c=1-(1-p)³ Meanwhile, actual observations on occurrence proportion of catch in branches (P) are obtained by P=B/B_o, where B_o 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 (P_c) 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.