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.Keywords: Chum salmon; Aerial census; Radio-controlled helicopter; Salmon escapement; Salmon abundanceHighlights  Chum salmon were identified in photographs taken from a radio-controlled helicopter  Spawning redds were also distinguishable in aerial photographs  Counts are significantly positively correlated with independent abundance estimates  This census is a cost-effective method for abundance estimation of salmon in rivers

Thyroid hormone (TH) plays an important role in regulating multiple cellular and metabolic processes, including cell proliferation, cell death, and energy metabolism, in various organs and tissues of vertebrates. It is generally accepted that anadromous Pacific salmon (Oncorhynchus spp.) imprint odorants from their natal stream during their seaward migration, and they then use olfaction to discriminate their natal stream during the spawning migration. Both serum TH levels and the specific binding values of TH in the salmon olfactory epithelium were markedly increased during the seaward migration. However, thyroid hormone receptor (TR) expression in the olfactory epithelium has not been confirmed in vertebrates. We investigated gene expression of TR isoforms in chum salmon (O. keta) by both molecular biological and histochemical techniques. Expression of TRβ mRNA was detected in the olfactory epithelium by reverse transcriptase polymerase chain reaction (RT-PCR). Nucleotide sequencing demonstrated the existence of a remarkable homology between the RT-PCR product and part of the ligand-binding domain of other teleost TRβ isoforms. By in situ hybridization using a digoxygenin-labeled salmon olfactory TRβ cRNA probe, signals for salmon olfactory TRβ mRNA were observed preferentially in the perinuclear regions of immature olfactory receptor neurons (ORNs), as protein gene product 9.5 (PGP9.5)-immunopositive ORNs. Our results provide the first detection of TRβ gene expression in the olfactory epithelium, and suggested the possibility that TRβ may be involved in cell maturation and/or cell differentiation of the ORNs in Pacific salmon.