Columbia River Basin State of the River Report for Toxics - Indicators
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What are Environmental Indicators?
Environmental indicators are used to help us understand the health of the environment and whether we are reaching our environmental goals. The indicators chosen for this report are animal groups that live in or depend on food from the Basin. Studying these animals over time will help us track changes in the Basin’s ecosystem.
Which Indicator Species are Used in this Report?
Juvenile salmon
Juvenile salmon are an important indicator of ecosystem health in the Basin because:
- they are relatively widespread throughout the Basin,
- they forage for food in the River system and also serve as a major food source for larger fish, birds, and mammals,
- they use many types of Basin habitat which helps us assess environmental conditions throughout the River system,
- they go through physiological changes from juvenile to adult and so can be more susceptible to toxic contaminants, and
- currently, 13 species of salmon and steelhead in the Basin are on the Endangered Species list
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Resident fish
There are many native and non-native resident fish species in the Basin, including rainbow trout, cutthroat trout, mountain whitefish, large scale sucker, bass, walleye, and northern pikeminnow. They are a common source of food for people and wildlife and are widely distributed throughout the Basin. In many of the Basin’s water bodies, these resident species have accumulated levels of some contaminants that are harmful to predators and to people.
Resident fish are good indicators because:
- they are widespread in the Basin;
- most current information on contaminants in the Basin are from resident fish;
- many resident fish spend their lives in relatively small areas, so their contaminant levels show us the contaminant loads in those areas; and
- they occupy a central place in the food web, are exposed to contaminants through their diet, and in turn expose those who eat them, including people, to any accumulated contaminants.
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Sturgeon
Sturgeon are the largest freshwater fish in North America, occurring in Pacific Coast rivers from central California to Alaska’s Aleutian Islands. Some white sturgeon spend their entire life cycle in freshwater, while others use estuarine or coastal saltwater resources for growth and food, only entering freshwater to reproduce. White sturgeon are a good Columbia River indicator species because:
- they are widely distributed in large rivers of the Basin;
- they are long-lived and thus have prolonged exposure to toxic contaminants,
- sturgeon migration is curtailed by dams in some portions of the Basin, allowing for evaluation of local toxics effects;
- they are near the top of the food web, and
- effects of contaminants on sturgeon are likely similar for other benthic, bottom-dwelling species.
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Predatory birds: Osprey and Bald Eagle
Osprey and bald eagle are large birds of prey that live in much of the Basin, but they are concentrated in the Lower Columbia River. Osprey and bald eagles are useful indicators for evaluating the health of an aquatic ecosystem for several reasons:
- they are widely distributed;
- they are long-lived (bald eagles can live up to 28 years in the wild);
- they eat fish and other River predators, usually near their nests; and
- they are at the top of the food web and so are exposed to high concentrations of contaminants through their diet.
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Aquatic mammals: Mink and River Otter
Mink and river otter are both found throughout the Basin in appropriate habitat; however, mink populations have not recovered from a decline in the 1950s and 1960s, even though suitable habitat is available for them in the Lower Columbia River.
Mink and otter are useful indicators of ecosystem health in the Basin because they:
- prey on other aquatic species;
- are particularly sensitive to contaminants which accumulate and can impact their reproduction;
- have smaller home ranges compared to osprey and bald eagles; and
- occur throughout the Basin.
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Sediment-dwelling Shellfish—Asian clam
The non-native, freshwater Asian clam is a small, light-colored bivalve widely distributed throughout a large portion of the Basin. Asian clams are a good indicator species for several reasons:
- they are filter feeders and, like other freshwater shellfish, can collect and concentrate contaminants in their bodies,
- they are not very mobile, so data on clams can be more useful to pinpoint the location where they were exposed to the contaminants than similar or more mobile species,
- because of their distribution and feeding habits, they are a useful indicator of sediment and water quality conditions in the Basin, and
- they occupy a lower position in the food web than other indicator species.
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