One of the most well known environmental battles involves the struggle between the need for hydroelectric dams on the Columbia and Lower Snake rivers vs the need for healthy spawning habitat for salmon. This battle has had many dimensions but, so far, no real solutions have emerged. The reason for this is emblematic of many environmental problems - it depends largely on how the problem is framed and what data is used to define the problem.

Let's first start at the issue of dams causing the decline of salmon. The principle hypothesis here is whether or not dams have cause a "catastrophic" loss of population. We can use salmon count data as a means of establishing a baseline and to see if there is a decline in that baseline over time. We can then convolve that data with the following simple model:

X ----------|-------------|--------|------|--------|----|---|--|->  X'

            1             2        3      4        5    6   7  8

Suppose we have a system where X salmon enter and have to pass 8 dams to reach X'. The issues are:

• How many fish are eliminated by the first dam
• how many are eliminated by success dams?
• does fish survival probability depend on dam size? distance from the mouth of the columbia river (assumes salmon get tired and find fish ladders more difficult to negotiate); salmon learning curve (assumes that salmon learn to look for fish ladders along the way thus reducing the mortality rate).

Under the model where all dams are equal then we should see something like this in the data.

X₁ < X₂ < X₃ < X₄ < X₅ < ...

While there may be other complicating factors such as salmon spawning tributaries between dams, it is reasonable to assume that the upstream migration pattern takes a hit each time that pattern encounters a dam. At least that is what we believe the outcome should be. These hypothesis can be tested to some extent by the actual salmon count data which exists at each dam ( Link to actual count data ) that exist within this overall system

The above shows the wave form of the historical salmon counts at Bonneville dam from 1935 to 2005: all counts at the other dams show similar wave forms. There a number of important and complicating features of this diagram that bear directly on the environmental issue of salmon decline.

1. Clearly the salmon counts are cyclical in nature ( see this visualization ), alternating between peaks and troughs on various timescales. This is most likely related to similar variations in PNW climate that determines river temperature and stream flow.

2. Salmon started to become an environmental icon in the mid 1990's which was clearly one of the cyclical times of low salmon. Salmon counts at this time were about a factor of 2 below what was seen in the mid 1980's and this lead to cries of salmon decline. Within this context, its important to note that the last dam built in the system was completed in 1972. Bonneville dam was constructed in 1935 and by the late 1950's McNary and the Dalles dam was constructed - yet its hard to see evidence of dam construction in this historical wave form.

3. There seems to be some kind of "natural" minimum floor of about 200,000 salmon. None of the low periods dip beneath that.

4. The period 2001--2004 represents and enormous increase in the observed Salmon. This was not caused by an increase in salmon detection efficiency but instead this represents truly record salmon runs on the Columbia river, which is likely a manifestation of the "success" of the fish hatchery industry.

5. Since 2004 there has been a precipitous drop in the salmon counts, much more strongly than the 1985 to 1995 drop. This is most likely a reaction to adverse climate conditions in the region. Your last homework assignment will ask you to extend the above wave form to more recent years.

Thus the salmon decline issue is complex and there are many factors at work that can affect various aspects of this environmental problem. The following table tries to summarize this complexity:

Salmon Decline Matrix

Problem	Dams	Logging	Changing Climate	Agriculture	Pop. Growth	Over Fishing	Other
Salmon Migration Barriers	Big Time	no	no	no	no	no	no
Barriers to Reaching Spawing Grounds	Yes	no	Yes	no	no	Yes!	no
Reduced Number of Young Salmon reaching sea	yes	yes	no	no	no	no	bird predation
Pesticide Exposure	no	Yes	no	Yes	no	no	no
Industrial Pollutants Exposure	no	no	no	no	Yes	no	no
Loss of Streamside Vegetation and Functions	no	Yes	no	Yes	Yes	no	no
Increased Sediment Load	no	Yes	Yes	Yes	Yes	no	no
Natural Habitat Destruction	yes	yes	no	yes	yes	no	no
Reduced Fresh Water Flow in Rivers and Streams	yes	no	no	yes	yes	no	no
Abnormal water temperatures	yes	no	yes	yes	no	no	no
Reduced upwelling and nutrient/food supply	no	no	yes	no	no	no	competition with hatchery fish
Estuary Degradation	no	Yes	no	no	Yes	no	no
Loss of cool deep pools in streams	no	Yes	no	no	no	no	no

If your seriously interested in this environmental issue then you read the the extensive annual report as well as this resource and this one

Finally, a few words about escaped salmon from fish farms:

The reason the issue of escaped salmon deserves our attention is that there are legitimate environmental concerns that result from a farmed fish escaping. In British Columbia, both Atlantic and Pacific salmon are being raised in farms and each of these two species poses unique risks once they do escape. For Atlantic, there's hybridization, which is basically Atlantic and salmon crossbreeding -- Atlantic and Pacific salmon crossbreeding. The other is predation and competition. This involves the Atlantic feeding on wild Pacific salmon, as well as other food supplies, and then the taking of space and the wild habitat in general.

Another major concern is spawning site disruption by Atlantic salmon. The stems from the fact that Atlantic salmon spawn later than Pacific salmon so there's a risk that they enter the same streams that the Pacifics have already spawned in and then they disrupt the eggs that the Pacific salmon have already placed. And also, Atlantic salmon mature faster than Pacific salmon, and so they have a competitive, or they give to the Pacific salmon a competitive disadvantage due to their smaller size. Another concern is colonisation of Atlantics in BC, which would have severe impacts on the wild stocks -- mainly because they would be using the same streams that wild Pacific stocks presently use to spawn. And finally, there is the issue of the spreading of diseases from the farmed salmon to the wild Pacific salmon.