The life history and populations of chum salmon (Oncorhynchus keta) in China: an otolith isotopic investigation

Abstract Stable isotope ratios of otoliths (δ13C and δ18O) can be used as a habitat index in anadromous fish, because there are marked differences between freshwater and marine settings. Here we report the results of 84 otoliths of chum salmon (Oncorhynchus keta) collected from three locations (Site-A, Site-B, and Site-C) in China, where all the estuaries for chum salmon ocean entry are located in Russia or North Korea and no biological observation data being obtained. In this study we adopted a blind-test protocol and applied stable isotope analyses in chum salmon otoliths. Two aragonite powder samples were taken from each otolith: one from the nucleus of otoliths; the other from the 2nd summer growth zones. Overall the δ13C values of chum salmon otoliths ranged from -10.9 to -4.0‰, whereas δ18O values of the same samples ranged from -6.4 to +1.9‰. Based on δ18O values at about -3.5‰ (the boundary line), two different spawning populations or stocks have been identified (p-value =0.008). The Site-A samples were initially collected from the Amur River, while the Site-B samples were collected from the Tumen River. The Suifen River (Site-C) samples had some mixing with the Amur River chum salmon, but they were essentially classified into the Tumen River population. Comparison between our data and the previously reported sockeye salmon and chinook salmon data in North America indicated that the chum salmon in China are anadromous, and have the same life history from freshwater to marine as other populations over the world.