Recent production trends of chum salmon Oncorhynchus keta under conditions of warming climate

Pacific salmon (Oncorhynchus spp.) play an important role as a keystone species and in ecosystem services in the subarctic North Pacific. Planktivorous pink (O. gorbuscha) and chum salmon (O. keta) abundance has increased since the 1975/76 regime-shift until the present, but their abundances have shown stable or declining trends in Canada, Japan, and USA since the 1990s, even though Russian chum and pink salmon abundance have been increasing (Fig. 1). Run size of Japanese chum salmon showed a decreasing trend in Honshu Island since the late 1990s and in Hokkaido Island since the early 2000s (Fig. 2). The carrying capacity of sockeye (O. nerka), chum, and pink salmon has changed to a downward trend since the early 2000s (Kaeriyama et al. 2011). Abundance of wild chum salmon in the 1990s decreased to 50% below that of the 1930s, while there have been significant increases in hatchery populations (Kaeriyama et al. 2009). Hatchery-derived salmon genetically disturb native-wild Pacific salmon. Araki and Schmid (2010) examined 266 peer-reviewed papers on effects of hatchery fish stocking on wild stocks and the consequences for stock enhancement. They concluded that negative effects of hatchery rearing on a variety of fish species are common and there are few indications of successful stocking. Hatchery-derived chum salmon have lower genetic diversity than wild salmon (Okazaki 1982). Yokotani et al. (2009) surveyed the population structure in the Yurappu River using mitochondrial DNA (mtDNA) analysis. Yurappu River chum salmon showed eight haplotypes (Ht1-Ht8) in the 481 bp 5’ variable portion of the mtDNA control region (Fig. 3). Pairwise population FST estimates showed that the December-run population (YPD) differed significantly from the October-run population (YPO) in the Yurappu River. The YPO population was closely related to others, such as the Chitose, Tokachi, and Nishibetsu river-populations (Table 1). These results suggest that Yurappu River chum salmon are genetically different and perhaps reproductively isolated by run-timing. It is thought that the native population persists as the late-run timing component, and that the early-run

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