Vertical Distribution of Catch in Coastal Set-line

Abstract

Tama-nawa is a variety of small bottom long-line employed in Sagami Bay. This is constructed of a number of branch lines attached to a main line at intervals of 20-30m. Each branch line is constituted in the shape of vertical long-line with five baited hooks, which are distributed at very narrow vertical intervals within the layer of a few meters above the sea bed. So that, the catchability is considered to be wider in the vertical, than common types of bottom long-lines in which the main line, branch lines as well as hooks are set directly on the sea bed.
By using these characteristics of the gear construction in Tama-nawa, relationships of catch and the height of each hook form the sea bed was examined, in order to discuss the vertical distribution pattern of catch in demersal fishes.
As a result, two patterns of catch distribution could be classified. One is the exponential distribution pattern, in which most of catch was obtained near the sea bed and few at some distance from the sea bed. The other is adapted to a normal distribution pattern, which shows the concentration of catch at a certain positon away from the sea bed. These patterns show variation according to the operation time, in terms of concentration.