(PLEASE NOTE: These web pages are for archival purposes only and are no longer maintained. For current information on this topic at the AFSC visit the Ecosystem Monitoring and Assessment program. )

Long-term monitoring of changes in age- and size-at-maturity of Pacific salmon by Ocean Carrying Capacity scientists has occurred since the late 1950s. Annual stream surveys consist of field sampling of scales, length, and weights from the carcasses of chum salmon that spawned and died in rivers ranging from southcentral Alaska to Washington. Long-term monitoring of salmon age- and size-at-maturity is used to evaluate the influence of marine climate and population abundances on the dynamics of salmon and marine fish populations.

Fig. 1. Scientists at work during their annual stream surveys collecting scales, lengths, and weights from chum salmon carcasses.

Pacific salmon (Oncorhynchus spp.) abundance in Alaska has reached record levels since the mid-1980s (Fig. 2). Significant reductions in body size (Fig.3) and increased age at maturity in chum salmon (Oncorhynchus keta) occured throughout chum salmon populations in Alaska and the North Pacific as abundance levels of salmon increased. Chum salmon weight reductions have approached 50% in both Washington and southeast Alaska chum salmon populations. The coincident decline in size of chum salmon and large increase in abundance from the mid-1970s to the mid-1990s supported the belief that the ocean carrying capacity for salmon production had been reached. However, the ocean carrying capacity for salmon is dynamic and is expected to respond to changes in ocean productivity and climate. Abrupt increases in body size of chum salmon during the mid-1990s emphasizes the dynamic nature of ocean carrying capacity and the need for monitoring and ocean observation studies to adequately address ocean carrying capacity for salmon.

Fig. 2. Total annual commercial catch of Pacific salmon in Alaska waters from 1880 to 2005.	Fig. 3. Mean body length of male age-4 chum salmon at Fish Creek near Hyder in Alaska from 1972 to 2006.

Supporting Research

• Helle, J.H. and M.S. Hoffman 1995. Size decline and older age at maturity of two chum salmon Oncorhynchus keta in western North America, 1972-92. Pages 245-260. In R.J. Beamsih, editor. Climate Change and Northern Fish Populations. Canadian Special Publication of Fisheries and Aquatic Sciences 121, Ottawa, Ontario, Canada.
   
• Helle, J.H. and M.S. Hoffman 1998. Changes in size and age at maturity of two North American stocks of chum salmon (Oncorynchus keta) before and after a major regime shift in the North Pacific Ocean. N. Pac. Anadr. Fish. Comm. 1: 81-89.
  
  
• Helle, J.H. and E.C. Martinson 2007. Potential to build groundwater spawning channels for chum salmon near Hyder, Alaska. Bilateral Northern Panel of the Pacific Salmon Commission meeting, January 10, 2007.
  
  
• Helle, J.H., and E.C. Martinson 2006. Marine conditions and ocean-wide effects on the size of salmon. Yukon River Drainage Fisherman Association, October 30, 2006.
  
  
• Helle, J.H., D. Eggers, O.F. Gritsenko, Y. Ishida, and E.C. Martinson 2005. Biological characteristics of Pacific salmon as indicators of North Pacific climate and ocean conditions. North Pacific Anadromous Fish Commission-PICES Joint Symposium, Korea, December 2005.
  
  

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