In order to solve problems of the characteristic movement of trolling gear, experiments were conducted in Kagoshima Bay in calm conditions by the research ship, Nanseimaru (83 G. R. T.). The tension of trolling line using two kinds of leader, i.e. nylon monofilament and sekiyama (ganged wire leader) for trolling depressor, were measured by a load cell which was fixed at the tip of a steel pipe, and were recorded on a data-recorder. These data were analyzed in the laboratory. Power spectra were estimated from these data. Dominant fre-quencies in these spectra were identified; one was a frequency of 0.2Hz ley with a propor-tional speed increase, while the other was a the frequency of 6.0Hz with a slight proportional speed decrease. The former occupied a major portion of the spectra, which suggested the movement of the whole trolling gear. The movement of the trolling gear suggested that two periodical components, i.e. about 5.0 seconds and about 1.7 seconds, were combined with different frequencies. Considering the information on the numerical filter process, the move-ment of the whole trolling gear was effected by differences in the material used in its leader.
