SEARCH BEHAVIOR IN THE PURSE SEINE TUNA FISHERY

Abstract

A purse seine vessel cruises in search of schools of tuna during daylight hours, attempting to locate fish by observing surface water disturbance, sea bird activity, or floating objects. The purpose of this paper is to examine the two hypotheses advanced by Doulman: that the Japanese vessels have a greater tendency to fish as a fleet than the US vessels and that they have a greater tendency to exchange information about fishing conditions. Section 2 describes a sample of data on the operations of Japanese and US purse seiners in Papua New Guinea's exclusive economic zone (EEZ) in the years 1983-1987. Section 3 examines and compares the spatial distribution of the two fleets in the EEZ to determine whether there is evidence of a more concerted approach to fishing on the part of the Japanese as compared with the US vessels. In Sections 4-6 the hypothesis that there is a greater amount of information sharing among Japanese than among US vessels is tested in various ways. Section 4 analyzes vessel movements as a possible response to catch returns. Section 5 analyzes the success rate in terms of locating and catching schools and its relationship to the number of vessels involved. Section 6 models vessel behaviour as a response to Bayesian udpating of information. Finally, Section 7 briefly summarizes the conclusions of the paper.