EFFECT OF SOAKING TIME ON CATCH-PER-UNIT-EFFORT OF MAJOR SPECIES TAKEN IN THE JAPANESE SQUID DRIFTNET FISHERY IN 1990

We made a preliminary analysis of the effect of soaking time on the catch of the Japanese squid driftnet fishery in the central North Pacific in 1990. In a typical fishing operation, eight or nine net sections (each 4-7 km long) were used. Net retrievals began from the last section deployed, The soaking time for each section ranged from approximately 5 to 19 h, based on 993 fishing operations by 75 vessels monitored by scientific observers from Canada, Japan and the USA. The relationship between soaking time (indexed by section retrieval order number) and average catch in number per net panel or tan (catch-per-unit-effort, CPUE) revealed three patterns depending on the species entangled. These patterns included: (1) positive relationship between CPUE and soaking time throughout the sections (blue shark and salmon shark); (2) positive relationship within the first three to six sections, which were probably retrieved during the night and dawn, but constant or slightly decreased CPUE in later sections retrieved in day time (neon flying squid, Pacific pomfret, seabirds); (3) negative relationship (pelagic armorhead). These different patterns were considered to represent primarily the behavior of species, diel vertical migration or diel feeding activity, and secondly drop out from the nets and predation.