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1; Beamish and Bouillion, 1993;. Kaeriyama, 1998; Klyashtorin, 1998). Kaeriyama (2003) defined the carrying capacity (K) of sockeye (O. nerka), chum (O. keta).
Carrying capacity and life history strategy of Pacific salmon in relation to long-term climate change Masahide Kaeriyama Graduate School of Fisheries Science, Hokkaido University, Hokkaido, Japan (salmon@fish.hokudai.ac.jp) Pacific salmon occupy high trophic levels in the North Pacific Ocean ecosystem (e.g. Aydin et al., 2003; Kaeriyama, 2003), and are important not only as fisheries resources but also for keystone species in this ecosystem.

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Figure 1. Annual changes in catch of Pacific salmon and PDO in the North Pacific. Arrows and bars indicate the regime shift year (Kaeriyama 1998).

Carrying capacity The change in biomass of Pacific salmon (Oncorhynchus Oncorhynchus spp.) indicates a 30 or 40 year periodicity coinciding with longterm climate changes (Fig. 1; Beamish and Bouillion, 1993; Kaeriyama, 1998; Klyashtorin, 1998). Kaeriyama (2003) defined the carrying capacity (K) of sockeye (O. nerka), chum (O. keta) and pink salmon (O. gorbuscha) using the replacement level of the Ricker recruitment curve and the residual carrying capacity (RCC): RCC= (K-biomass)K-1. A significant positive correlation was observed between the Aleutian Low Pressure Index (ALPI) and the carrying capacity at

Figure 2. Temporal changes in carrying capacity (K) of three species of Pacific salmon (sockeye, chum and pink salmon) and the Aleutian Low Pressure Index (ALPI) (Kaeriyama, 2003).

Figure 3. Relationship between residual carrying capacity (RCC) of Hokkaido chum salmon population and mean fork length (FL) of age 4 female adult returning to the Ishikari River (A), or mean age at maturity of the Hokkaido chum salmon population (B) (Yatsu and Kaeriyama 2005).

the species level (Fig. 2). Factors affecting the carrying capacity of chum salmon, such as reproductive regimes (e.g. survival rate and sea surface temperature (SST) in the early marine life period), differed at the population level (Yatsu and Kaeriyama, 2005). The RCC was significantly positively correlated with body size and negatively related to age at maturity in Hokkaido chum salmon populations (Fig. 3). The biomass of wild chum salmon populations in the 1990s decreased 50% below that of the 1930s, despite the significant increases in hatchery populations (Fig. 4). This indicates that biological interaction between wild and hatchery populations should be an important issue in the sustainable management of Pacific salmon production based on the ecosystem level.

Figure 4. Annual change in biomass of chum salmon in the North Pacific Ocean during 1925-2001 (Kaeriyama 2003).

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Aota M. 1999. Long-term tendencies of sea ice concentration and air temperature in the Okhotsk Sea coast of Hokkaido. PICES Science Report 12: 1-2. Aydin K.Y., G.A. McFarlane, J.R. King and B.A. Megrey. 2003. PICESGLOBEC international program on climate change and carrying capacity. The BASS/MODEL report on trophic models of the Subarctic Pacific basin ecosystems. PICES Science Report 25: 1–93.

Beamish R.J. and D. Bouillion. 1993. Pacific salmon production trends in relation to climate. Canadian Journal of Fisheries and Aquatic Science 50: 1002–1016. Beamish R.J., C. Mahnken and C.M. Neville. 2004. Evidence that reduced early marine growth is associated with lower marine survival of coho salmon. Transactions of the American Fisheries Society 133: 26-33. Healy M.C. 1982. Timing and relative intensity of size-selective mortality of juvenile chum salmon (Oncorhynchus keta) during early sea life. Canadian Journal of Fisheries and Aquatic Science 39: 952-957. Kaeriyama M. 1998. Dynamics of chum salmon, Oncorhynchus keta, populations released from Hokkaido, Japan. North Pacific Anadromous Fish Commission Bulletin 1: 90–102. Kaeriyama M. 2003. Evaluation of carrying capacity of Pacific salmon in the North Pacific Ocean for ecosystem-based sustainable conservation management. North Pacific Anadromous Fish Commission Technical Report 5: 1–4. Kaeriyama M., A. Yatsu, M. Noto, and S. Saitoh. in press. Spatial and temporal changes in growth pattern and survival of Hokkaido chum salmon populations during 1970-2001. North Pacific Anadromous Fish Commission Bulletin 4. Klyashtorin L.B. 1998. Cyclic climate changes and Pacific salmon stock fluctuations: a possibility for long-term forecasting. North Pacific Anadromous Fish Commission Technical Report 1: 6–7. Merzlyakov A.Y., E. Dulepova and V. I. Chuchukalo. 2005. Modern state of pelagic communities in the Okhotsk Sea. Abstracts of 14th PICES Annual Meeting. p.32. Yatsu A. and M. Kaeriyama. 2005. Linkages between coastal and openocean habitats and dynamics of Japanese stocks of chum salmon and Japanese sardine. Deep-Sea Research II 52: 727-737.

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References

Figure 6. Annual changes in the sea ice concentration (SI), the sea surface temperature (SST) in the Sea of Okhotsk, and growth anomaly at the Sea of Okhotsk (Lo) of age 4 chum salmon returning to the Ishikari River (Kaeriyama et al., 2006).

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Life history strategy I analysed scale length and number of circuli from the focus to the inner edges of check (Rcj and Ros) and annuli (r1–r4) on scales of female chum salmon collected in the Ishikari River during 1970-2001, and back-calculated individual growth in fork length from result of scale analysis (Kaeriyama et al., in press). In all age groups, growth at the first year increased in the 1990s. This growth increase at the first year occurred in the Sea of Okhotsk, but not in coastal waters of Hokkaido (Fig. 5). Growth of the Ishikari River chum salmon at the first year was negatively correlated with the sea ice concentration in winter, and positively correlated with the SST during summer and fall in the Sea of Okhotsk (Fig. 6), despite no relation between SST and zooplankton biomass (Merzlyakov et al., 2005). The positive correlation between the growth in the Sea of Okhotsuk and survival of the Hokkaido chum salmon population was also observed. Recently sea ice concentrations in the Sea of Okhotsuk have decreased presumably due to global warming (Aota, 1999). Chum salmon have two periods of critical mortality: 1) the early marine life period (Healey, 1982), and 2) the first wintering period in the ocean (Beamish et al., 2004; Moss et al., 2005). Therefore, these results suggest that recent increases in growth in the Sea of Okhotsk and survival of Hokkaido chum salmon population may be affected by the long-term climate change such as the global warming.

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Figure 5. Annual change in mean and SD of fork length of Ishikari River chum salmon by age at the first year (A), and growth in coastal waters of Hokkaido (Lc) and in the Sea of Okhotsk (Lo) during 1968-2001 (B) (Kaeriyama et al., 2006).

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