Introduction: An Overview of the Ocean Ecology of Pacific Salmon and Trout
Richard J. Beamish
Pacific salmon catches by all countries are at historic high levels, but in some areas and for some species such as Chinook Salmon Oncorhynchus tshawytscha and Coho Salmon O. kisutch, abundances are low, and ocean survival is poor. In general we do not understand enough about the mechanisms that regulate production of Pacific salmon to explain the current trends in abundance. There is general agreement that climate and ocean conditions have a major influence on production. For example, a major change in the intensity of the Aleutian Low around 1977 is generally acknowledged as improving the production of Pacific salmon that rear in the Bering Sea. Climate effects and habitat changes in fresh water have been shown to have important influences on Pacific salmon production, but the increasing production of Pacific salmon from hatcheries identifies the influence of the ocean as the fry and smolts spend only a minimum time in fresh water.
There is also general agreement that the increasing levels of greenhouse gases are changing the rearing environments of Pacific salmon in fresh water and in the ocean. Conservative models show that influences, such as increasing temperature, will continue, resulting in some habitats being unsuitable for rearing or at least becoming stressful. Thus, there is an urgency to improve the understanding of the mechanisms that regulate Pacific salmon production. There is an economic urgency because Pacific salmon support important commercial fisheries and all Pacific salmon producing countries have invested in hatcheries as a way of producing more salmon. There also is widespread interest in Pacific salmon because they are an iconic indicator of the health of our environment. All around the rim of the subarctic Pacific, it is expected that governments will want to ensure that there is effective stewardship of all Pacific salmon.