A Population Size Estimate of the Finless Porpoise, Neophocaena phocaenoides, from Aerial Sighting Surveys in Ariake Sound and Tachibana Bay, Japan

摘要

We estimated the population size of the finless porpoise (Neophocaena phocaenoides) in Ariake Sound and Tachibana Bay of western Kyushu, southwestern Japan, from aerial sighting surveys using line transect methods. All 12 surveys were conducted from May 1993 to May 1994 (8 in Ariake Sound and 4 in Tachibana Bay). In addition to these, 14 surveys were also carried out to obtain information on porpoise occurrence in Tachibana Bay (5 surveys) and in neighboring Sumo Nada (5) and Yatsushiro Sound (4). InAriake Sound, 225 porpoise groups (369 animals) were detected during all flights totalling 1,694.4 km. In Tachibana Bay, a total of 997.8km was surveyed and 55 groups (290 animals) were sighted. However, no sightings were recorded in Sumo Nada (distancesearched =148.7 km) and Yatsushiro Sound (208.4 km). In Ariake Sound, few sightings were recorded from waters shallower than 5 m in depth. In Tachibana Bay all animals were detected from waters of less than 50 m depth. The population size was estimatedas 1,983 animals in Ariake Sound (95% CI= 1,382-2,847), 1,110 in Tachibana Bay (95% CI=642-1,920), and 3,093 in the 2 waters (1.3 individuals/km~2, 95% CI = 2,278-4,201).