Cost-effective accurate estimates of adult chum salmon, Oncorhynchus keta, abundance in a Japanese river using a radio-controlled helicopter

Abstract This paper describes an attempt in 2008 to establish an aerial census of adult chum salmon using a small radio-controlled (RC) helicopter. The Moheji River, located in southern Hokkaido, was chosen because all the salmon in a stretch of the river between a weir and the estuary are seine-netted every morning for artificial propagation. Aerial photographs of the river were taken from a RC helicopter equipped with a digital single-lens reflex camera and polarized filter. To quantify salmon density within the census area, the number of salmon per aerial photograph was counted using image-processing software. Salmon could be clearly identified in photographs taken from an altitude of ∼30 m. Salmon numbers estimated by aerial census and seine-netting were significantly related. The results indicate that a small RC helicopter can be used to generate adult salmon abundance data in Japanese rivers.