Dolphins have highly developed sonar abilities and have been studied extensively in captivity. The use of sonar by dolphins and porpoises in the wild is thought to be related to the underwater navigation and searching behavior. Here we report a new and simple method to archive continuous click events individually. Echolocation click events and swimming speed of finless porpoises (Neophocaena phocaenoides) were recorded with data loggers attached on the animals. The echolocation range converted from sonar pulse intervals in open waters ranged up to 130 m. Echolocation of free-ranging dolphins appears to adapt to various distance in navigation or ranging. Silent swim distance, calculated by the swim speed multiplied by the duration of the non-echolocating periods, was smaller than the echolocation range. Finless porpoises are believed to examine their frontal area acoustically using echolocation. In other words, the observed finless porpoises swam without echolocation only in an already inspected area.