Effect of ocean environments on the properties of catch variation of Jack mackerel (Trachurus japonicus) in the Bungo Channel

Abstract

Catch properties of jack mackerel, Trachurus japonicus, in the Bungo Channel, where is well-known for an intrusion of warm water from the Pacific Ocean, were examined from the seasonal-regional relationship between variation of age-0 jack mackerel landings and hydrographic conditions. Age-0 jack mackerels were caught from May through October in the central region of the Bungo Channel, while in the southern region they were caught throughout the year. This seasonal-regional difference of the catches in the channel is probably caused by the warm water intrusion associated with the development of stratification in the central region. It is therefore suggested that the age-0 jack mackerels in the southern region move to north with the intrusion of warm waters. It was also distinct that the catches of jack mackerel in the central region strongly depended on a spring recruitment originated from the southern region. Sampling of jack mackerel larvae revealed that the intrusion of warm water in April was accompanied by the inflow of the jack mackerel larvae from the southern region. Inter-annual catch variation of age-0 jack mackerel in the southern region was found to be caused by the generation of the Kuroshio frontal eddy off the Channel.