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Biosphere, Climate, Oceans



In September of 1997 the ocean temperature increased to 69 degrees Fahrenheit in the northwest or 10 degrees above normal as warmer waters moved north along the Pacific west coast. A local fisherman snagged a 104 lb marlin that is typically found in warmer Baja California waters (NY Times article, 1997). Tropical yellowfin tuna were also represented in northwest Pacific waters. In northern California, tropical fish such as mahi mahi and swordfish swam the ocean waters. However, the warmer waters brought about by the fickle Pacific Ocean also wreaked havoc on other fish. Salmon, a cold water species, were especially susceptible to these environmental changes in the ocean. Mackerel migrated north with the warmer waters and preyed on young salmon just entering the ocean through river mouths. Furthermore, warmer waters resulted in the loss of millions of salmon during migration to streams where they hatched. The salmon were disappearing. Or were they?

Only recently have scientists discovered the reasons for the changes in ocean temperatures and their impacts on salmon. They noticed that in some years so many salmon returned to a hatchery that fisheries managers had to give them away. In other years, fishing boats remained at the docks because there were too few fish in the local ocean waters.

Although predicting salmon abundance is harder than predicting the weather, researchers also noticed another pattern: when Alaskan fishermen win, the Pacific Northwest (here defined as the region from N. California through Washington state) fishermen lose and visa versa. Some biologists and oceanographers think they might know why.

Searching through old issues of fishing journals, Steven Hare of the International Pacific Halibut Commission in the state of Washington was struck by the correlations he saw between Alaska and Pacific Northwest fisheries. Hare noted that in 1915, a reporter in Pacific Fisherman wrote that Bristol Bay (Alaska) salmon packers returned to port early due to a lack of fish. At the same time, the chinook salmon migration up the Columbia River that borders Oregon and Washington was the best in 25 years. In 1939, the Bristol Bay salmon run was touted as "the greatest in history," while the chinook catch down south was "one of the lowest in the history of the Columbia ( Rozell 1998 )."

The salmon numbers disparity occurred again in 1972, then more recently in 1994, when Alaska fisherman broke a record for salmon harvest while Washington and Oregon managers were forced to close the chinook fishery on the Columbia because so few fish were returning. The current woes of Pacific Northwest salmon fishermen are not due to salmon's preference for a northern life; Alaska and Pacific Northwest salmon rarely mingle, and many are of different species. So why the correlation between good years here, bad years there?

According to Hare and Nathan Mantua, an atmospheric scientist at the University of Washington, ocean conditions affect salmon. They found that the Gulf of Alaska and Bristol Bay since 1977 have been more suitable places for salmon than the northern Pacific off the coast of California, Washington and Oregon. In the twenty years before 1977, years when Alaska's fisheries were struggling, the northern Pacific waters were more suitable for salmon.

The researchers discovered that the alternating pattern of changing salmon abundance between Alaska and the Pacific Northwest has to do with a climate phenomenon similar to El Nino . Instead of El Nino's recurrence pattern once every three to seven years, the one that may affect salmon has phases that last 20 to 30 years. This Pacific Decadal Oscillation (PDO), as the researchers call it, has its strongest signature in the North Pacific Ocean, while El Nino's patterns originate near the equitorial Pacific.

The PDO flips back and forth between a warm and cool phase. During a cool phase, the Pacific Northwest has a more favorable environment for salmon than Alaska due to its cooler ocean waters. The opposite occurs during a warm phase of the PDO (see Images A and B ). Consequently, the remarkable characteristic of Alaskan salmon abundance over the past half-century has been the large fluctuations at interdecadal time scales which resemble those of the PDO (see Image C and Table 1 on the right).

The Pacific Decadal Oscillation (PDO) may be controlled by a large scale atmospheric feature off the coast of Alaska called the Aleutian Low,. The Aleutian Low affects the mixing characteristics in the upper ocean, which in turn affect the food chain salmon feed upon.


Your proposal to work in support of the Northwest Salmon Commission has been accepted. They want to get a better handle on the salmon forecast. They are wondering how the PDO influences the distribution of salmon in the area and how it impacts the economy and Native Americans. They are also interested in how to manage the conflicts between salmon advocates, farmers and hydroelectric power companies.


Date: 9/3/2009

Scenario Images:

Pacific Decadal Oscillation
(A) Typical wintertime Sea Surface Temperature (colors), Sea Level Pressure (contours) and surface windstress (arrows) anomaly patterns during warm (on the left) and cool phases (on the right) of PDO.
Larger image.
Images A and B: courtesy JISAO

PDO time series, 1900-2008
(B) 20th century PDO "events" persisted for 20-to-30 years, while typical ENSO events persisted for 6 to 18 months. The "cool" PDO regimes (in blue) prevailed from 1890-1924 and again from 1947-1976, while "warm" PDO regimes (in red) dominated from 1925-1946 and from 1977 through the mid-1990's.
Larger image.

Alaskan Commercial Salmon Catch, 1878-2007
(C) Historical records show salmon abundance resembles the Pacific Decadal Oscillation pattern. When salmon are abundant in Alaska, there is a decline in the Pacific northwest, and visa versa. Larger image. Image: courtesy Alaska Division of Commercial Fisheries

Table 1: Percent change in mean catches of four Alaskan salmon stocks following major PDO sign changes in 1947 and 1977
Table 1. Percent change in mean catches of four Alaskan salmon stocks following major PDO sign changes in 1947 and 1977 Dramatic salmon stock changes take place at the start of the cool phase (1947) of the PDO and again at the start of the warm phase (1977).
source: Mantua et al 1997

Pacific Northwest salmon play an important role in the regions marine and terrestrial ecosystems
(D) Salmon are important species in the food web of the region's diverse animal populations. Omnivores, like bears and humans, enjoy a fishy snack. More info. Image:

Salmon People: The role of salmon in Native American culture.
(E) Aboriginal communities located in northwest North America are among the oldest known fishing cultures in the world. Learn about the salmon people. Image:



Tree Rings Show PDO Cycle Back to 1661 (Cycle A)
This article shows that the tree ring records from western North America exhibit a multi-decadal pattern of wet and dry climate as far back as 1661.


Economic and Environmental Reasons for Saving Salmon (Cycle A)
This reference document explains the economic and environmental benefits of preserving salmon in the Pacific Northwest.


How does the environment determine the health of salmon? (Cycle A)
We can learn a lot about the health of our environment through observing salmon. This article describes the important environmental factors which influence salmon abundance. It also illustrates how human activities modify these factors.


How does the PDO explain the salmon distribution in Alaska and the Pacific Northwest? (Cycle A)
Salmon catch in Alaska and the Pacific Northwest reflect the changes in the North Pacific Ocean and atmosphere, particularly the PDO. This webpage explains which phase of the PDO (cool or warm) favors a larger catch in Alaska, and which phase favors a larger catch in the northwest. Other links provide information on climate change and ocean indices.


Salmon People: Aboriginal people and salmon (Cycle A)
The importance of salmon to the Native peoples of the Northwest is told in stories, myths and facts.


Saving wild salmon: Political problems and solutions (Cycle A)
This set of online resources are compiled by a coalition of conservation organizations, businesses and taxpayer advocates. Salmon conservation involves several major stakeholders. These articles and linked resources identify the various interest groups involved in salmon related problems.


The Great Salmon Run: Competition Between Wild and Farmed Salmon (Cycle A)
This comprehensive report by the World Wildlife Fund describes the complex issues surrounding the wild and farmed salmon market.


The Pacific Decadal Oscillation (PDO) and its relationship to salmon distribution (Cycle A)
The discovery of the Pacific Decadal Oscillation from salmon data.
This milestone article laid the foundation for the salmon-PDO connection.


The Pacific Decadal Oscillation and Satellites (Cycle B)
JPL-NASA describe the PDO and how satellite data have led to the identification of this important, long-term, oceanic feature. The webpage includes a Question & Answer section relating the PDO to El Nino/La Nina Southern Oscillation(ENSO)and western U.S. weather and climate.


Why Is Salmon Conservation Important? (Cycle B)
This report discusses the importance of conserving salmon ecosystems. Salmon represent a critical species for measuring the health of Northwest environments.


Aquaculture: Atlantic farmed salmon (Cycle C)
This document describes some of the problems encountered with farmed Atlantic salmon.


Climate variability and the variability in sardines and anchovies (Cycle C)
This report looks at sardine and anchovy catch in 3 different fisheries regions and the connection between these fish populations and climate variability. It shows why California is different than the other two locations.


Impacts of climate change on tuna fisheries (Cycle C)
The webpage describes the relationship between ocean conditions, especially ENSO (El Nino-Southern Oscillation) and the distribution of endangered tuna in the Pacific. A video link on the TOPP program shows how tuna are tagged and traced.


The controversial role of hatcheries in salmon production (Cycle C)
Because wild salmon have declined, 70-80% of coastal salmon are now produced through hatcheries. This Northwest Fisheries resource looks at the ways in which hatcheries have impacted wild salmon and the salmon industry as a whole.


Wild Salmon Ecosystem (Cycle C)
Video depicts wild salmon ecosystem, showing interaction of species. The U-tube video is accompanied by folk music.


Sample Investigations:


Hold the anchovies (Cycle A)
Bridge Ocean Education Center: Using Microsoft Excel, graph atmospheric and fisheries data from the Monterey Bay Aquarium Research Institute to look for evidence of the Pacific Decadal Oscillation (PDO) and its connection to fish abundance. Webpage includes lesson plans, resources and links to other oceanographic research and data.
Difficulty: intermediate


Impact of climate change on chinook salmon (Cycle B)
Two activities are described looking at the salmon population and the impacts of climatic change, such as the PDO, on marine life, particularly salmon. Lessons provide articles, data sets and Internet resources.
Difficulty: beginner


A climate for change-marine life down under (Cycle C)
Investigate climate change and its impact on marine and coastal environments using the three lesson plans available at this website. This Australian educational website provides some interactive activities allowing students to focus on different marine ecosystems and organisms. Several links to climate change resources are also present.
Difficulty: beginner




  • Science
    National Science Education Standards - Science Content Standards The science content standards outline what students should know, understand, and be able to do in the natural sciences over the course of K-12 education.
      • Science as Inquiry (Std A)
        • Abilities necessary to do scientific inquiry
      • Physical Science (Std B)
        • Structure and properties of matter
        • Motions and forces
      • Life Science (Std C)
        • Interdependence of organisms
        • Matter, energy, and organization in living systems
      • Earth and Space Science (Std D)
        • Energy in the earth system
        • Geochemical cycles
      • Science and Technology (Std E)
        • Abilities of technological design
        • Understanding about science and technology
      • Science in Personal and Social Perspectives (Std F)
        • Environmental quality
        • Natural and human-induced hazards
        • Science and technology in local, national, and global challenges
  • Geography
    Geography for Life: National Geography Standards, 1994
      Physical processes shape Earth’s surface and interact with plant and animal life to create, sustain, and modify ecosystems. The geographically informed person knows and understands:
      • The characteristics and spatial distribution of ecosystems on Earth’s surface
      The physical environment is modified by human activities, largely as a consequence of the ways in which human societies value and use Earth’s natural resources, and human activities are also influenced by Earth’s physical features and processes. The geographically informed person knows and understands:
      • How physical systems affect human systems
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