Independent Multidisciplinary Science Team

IMST Conceptual Scientific Framework

The recovery of wild salmonids in Oregon depends on many factors, including the availability of quality freshwater and estuarine habitats, favorable ocean conditions, and enlightened management of fish harvest. Salmonid habitats extend across Oregon and encompass all land uses. Estuaries provide a critical transition between freshwater and the ocean. The ocean area on which salmonids depend extends well beyond Oregon and is subject to fluctuations in productivity that markedly affect survival and subsequent reproduction. Fish propagation and fish harvest are critical activities by which humans directly affect anadromous fish. Given this complexity, the IMST has developed the following basic concepts to guide the development of reports and recommendations. These concepts apply across fish species and land/water uses typically considered in IMST reports, and are based on IMST’s interpretation of findings in current literature from a broad spectrum of scientific disciplines.

1.  Wild salmonids are a natural part of Pacific Northwest ecosystems, and have co-evolved with these ecosystems. The contemporary geological landscape of the Pacific Northwest of North America was established with the formation of the major river/stream basins of the region, approximately two to five million years ago. The abundance of these species at the time of Euro-American migration to Oregon was a reflection of more than 10,000 years of adaptation to the post-glacial environment and 4,000 to 5,000 years of adaptation to contemporary climatic, vegetation, and disturbance patterns. The salmonid stocks of today co-evolved with the environment over thousands of years, a much longer time period than that since Euro-Americans entered the Pacific Northwest landscape.

2.  Watershed and habitat conditions were historically dynamic, not static. The full recovery of wild salmonids is a long-term process operating within large-scale environmental fluctuations. At any given location, there were times when freshwater habitat quality was high and times when habitat quality was low. At any given time, there were locations where habitat quality was better and locations where it was worse. Over time, the location of high quality habitat shifted and fluctuated in total area.
Ocean habitat also exhibits dynamic change over several time scales. There are inter-decadal variations in climate, as well as shorter-term variations, that affect the ocean productivity for salmonids.

Wild salmonid stocks historically accommodated changes in their environment through a combination of four evolutionary factors. High genetic diversity provided the raw material for the evolution of varied life history forms in response to environmental change. Long-term genetic adaptation produced the highly varied life history forms of these species, providing the behavioral diversity needed to persist in a wide range of changing conditions. High fish abundance distributed in multiple locations (stocks) increased the likelihood that metapopulations and their gene pools would survive. Occupation of refuges (higher quality habitats) provided the base for recolonization of poorer quality habitat as conditions improved over time.  In addition, improved conditions in freshwater and estuarine habitats may have (and continue to) buffer salmonid populations from the effects of poor ocean conditions.

3.  Euro-American settlement and present-day land and water uses have altered natural environments and processes in ways that are not well-understood, and that have unknown long-term consequences for wild salmonids.  One of the legacies of salmonid evolution in a highly variable environment is the ability to colonize and adapt to new and changing habitats. Anthropogenic activities accentuate and interact with these environmental fluctuations altering salmonid populations in ways that are difficult to predict. The extent of anthropogenic disturbance in the Pacific Northwest is much larger today than prior to Euro-American colonization, and continued population and economic growth are expected to limit recovery of wild salmonid populations.
Since the mid 1850s, the rate and extent to which habitats and management have changed have exceeded the ability of salmonids to adapt. Although refuges exist, wild salmonid stocks are seriously depressed, as are the rate and extent to which recolonization occurs. Hatchery practices likely diminished the genetic diversity of salmonids, potentially limiting their physiological and behavioral diversity, and thus their ability to cope with environmental fluctuations.

4.  “Range of historical conditions” is a valid hypothesis upon which to build habitat management plans, but its application should be informed by understanding of the likely effects of climate change.  The best available science suggests that restoring or enhancing ecosystem processes and structures to reflect the range of conditions within which wild salmonids evolved provides hope for ensuring their survival.  High quality habitat for wild salmonids was the result of naturally occurring structures and processes that operated across the landscape and over time.These same processes and structures occur today, but humans have altered their extent, intensity, frequency, and nature. Humans will continue to exert a substantial force on the terrestrial, freshwater, coastal, and marine ecosystems of the Pacific Northwest.

The persistence and abundance of salmonids under historical ecological conditions is evidence that those habitats were compatible with salmonid reproduction and survival. The historical range of ecological conditions and the diversity of salmonid stocks in the Pacific Northwest are important because they provide a framework for developing policy and management plans for the future. The use of these concepts in land and resource planning must also take into account that the future environment may be considerably different than any environments experienced in the past.