Theme G: Adapting to change: climate, habitat and socio-economics
52. CURRENT HATCHERY PROGRAMS AND FUTURE STOCK MANAGEMENT OF CHUM SALMON IN HOKKAIDO, NORTHERN JAPAN
Yasuyuki Miyakoshi*, Mitsuhiro Nagata, Shuichi Kitada, and Masahide Kaeriyama
Salmon and Freshwater Fisheries Research Institute, Hokkaido Research Organization, 3-373 Kitakashiwagi, Eniwa, 061-1433 Hokkaido Japan
miyakoshi-yasuyuki@hro.or.jp
Since the late 20th century, the biomass of Pacific salmon in the North Pacific has increased and recent biomass is at a historically high level. Japanese chum salmon Oncorhynchus keta has contributed to the increase of salmon biomass; 61-72% of total commercial chum salmon catches in the North Pacific in 2003-2007 (NPAFC).
Hokkaido, northern Japan, is the principal area of salmon production in Japan. To support commercial chum salmon fisheries, a hatchery stock enhancement program began in the 1880s and has been conducted for over 120 years. The number of chum salmon returning to Hokkaido rapidly increased during the last quarter of the 20th century and has ranged from 33.5 to 60.5 million fish in the last 10 years. Recent high returns have been attributed mainly to the successful hatchery programs (Kaeriyama 1999), favourable oceanic conditions, and closure of high-seas fisheries (Morita et al. 2006).
The number of hatchery-reared chum salmon released in Hokkaido peaked in the 1980s, and thereafter, by reducing ineffective stocking; the annual number is recently ~one billion fish (Fig. 1). For the current hatchery programs, as many as 1.27 million spawners are taken for broodstock and used for artificial fertilization. Although such intensive hatchery programs have been conducted over more than 20 generations, Beacham et al. (2008) found no evidence that Japanese chum salmon populations have lower genetic diversity than populations from Russia and North America. The recent return rates of Hokkaido chum salmon have demonstrated no declining trend although inter-annual fluctuation has been observed and the fluctuation pattern in return rates differed among regions within Hokkaido.
Thus, at present, the hatchery program of chum salmon in Hokkaido is successful for the purpose of increasing commercial catches, even if factors other than improvement of hatchery techniques have contributed to the recent high returns. Large numbers of hatchery fish are a dominant feature of chum salmon management in Japan and will likely remain so in the future. However, if the management of salmon is to succeed over the long-term it is important that self-sustaining populations and healthy spawning habitats persist (Mobrand et al. 2005). Unfortunately, information on naturally spawning chum salmon in Hokkaido is scarce, and therefore, assessment for naturally spawning populations commenced in 2008. Monitoring both hatchery- and natural-origin chum salmon is important and a novel strategy to properly manage chum salmon populations in Japan should be modelled and conducted.
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