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The Salmon Decline

ENVS 202 On-line Access


The Decline of the Northwest Salmon?

The apparent decline of the salmon in the Columbia river system is one of the most complex environmental problems we have.

However, this problem has been over-simplified by the media and others to one single root cause, namely the construction of hydroelectric dams on the Columbia river system.

Today we wish to access of this simplification is valid. The next homework assignment given will allow you to explore this issue in more depth as well. For today we want to examine some of the broader issues and look at the actual data which is available.

The Salmon controversy is an excellent example of arguments made largely on belief, instead of knowledge that is supported by the actual data .

It is also an excellent example/reflection of another problem that effectively prohibits meaningful discourse; reactive vs proactive positions

Factors Causing Salmon Decline:

Broad Brush Factors:

  1. Dam Construction
  2. Increased Logging
  3. Changing climate patterns
  4. Agriculture
  5. Increased population growth
  6. Over fishing

More Detailed Factors in relation to Above:

  • Loss of Streamside Vegetation and Functions (2,4,5)
  • Pesticide Exposure (2,4)
  • Industrial Pollutants Exposure (5)
  • Increased Amount Of Sediment Entering Streams (2,3,4,5)
  • Habitat Destruction or reduced area (1,2,4,5)
  • Decreased Amount Of Large Logs In Streams And Loss of Deep Pools and Channel Form (2,5)
  • Reduced Fresh Water Flow In Rivers and Streams (1,4,5)
  • Exposure to Abnormal Temperatures (1,3,4)
  • Lack of Screening of Water Diversion Canals to Keep Fish Out (4)
  • Reduced Upwelling (3)
  • Altered Ocean Currents and Flow (3)
  • Decreased Food Abundance (3)
  • Reduced Numbers of Adults Reaching Their Spawning Grounds (3,6)
  • Reduced Numbers of Young Fish Making It To The Sea (1,2, bird predation)
  • Barriers Preventing Salmon From Migrating Upstream or Downstream (1)
  • Competition Between Hatchery and Wild Fish
  • Forest Fragmentation (2,5)
  • Estuary Degradation (2,5)

    Let's look at some data. Most of this data comes from fish counts done at Bonneville Dam starting in 1938 (again the next homework assignment will have you make use of this data):

    Blue line represents growth of non-harvested fish in the Columbia River system. The implication is that competition for food/nutrients is increasing rapidly.

    Its getting warmer earlier in the season with time in the Columbia river. Is this cause local (e.g. dams/ag) or global (e.g. Global Warming)

    Graph shows harvesting by Tribal communities with protected fishing rights. Some degree of "over harvesting" is apparent.

    Graph shows total salmon catch off the coast of North America (including Alaska).

    Decline of In-River catches which is frequently used as the "best" indicator for overall salmon decline in the Columbia River System:

    Implication is that increases in ocean catch are directly responsible for decreases of in-river catches also shown.

    During class a student made a fairly perceptive comment on the Ocean catch figure. She pointed out that the increase could be due to an increase in efficiency of catching salmon instead of just more boats on the water catching salmon. This has important implications:

    • If the increase in Ocean catch is due to more boats (which is what I *believe* but can't prove) - then the Salmon population could be stable and less salmon simple reach the river systems.

    • But, if we have an increase in efficiency in the way we catch Salmon then its possible that the ocean Salmon count is actually declining and the increase in ocean harvest is due to this increase in efficiency. But again, this efficiency increase would have to be large.

      That is, if the true salmon count is down by a factor of say 100, relative to what it was 100 years ago, then our salmon efficiency in harvesting would have to increase by at least a factor of 100 to make up the difference. I think this is unlikely.

    This is the raw salmon count data at Boneville Dam that we will inspect more closely below. Evidence of quasi-cylical behavior is apparent.

    Some relevant WWW resources for the above:

  • The Great Salmon Hoax
  • Comprehensive data source on Northwest Fish
  • Pacific Interdecadal Climate Change
  • HydroPower and the Columbia River System
  • Don't forget about Canada

    Using the fish count data, can we determine if there is a significant decline? Yes, we can determine this from the statistical tools we have been talking about.

    Comparing Two Sample Means - Find the difference of the two sample means in units of sample mean errors. This works as follows:

    • Sample 1 has mean M1 and error in the mean E1
    • Sample 2 has mean M2 and error in the mean E2

      Difference in terms of signifance is:

      Simple Approximation:

      • If E1 and E2 are similar then use (M1-M2)/1.5E1

      • If E1 > 2*E2 then use (M1-M2)/E1

      The actual salmon count data:

      This distribution, defined by 44 points, has a mean of 358,000 salmon with a dispersion of 82,000 salmon. The error in the mean is 12,000 (82000/(square root of 44))

      Points to note about the distribution:

      1. The dispersion is fairly large. Is this intrinsic to the population or a reflection of measuring errors because salmon counting is difficult and unreliable.?

      2. There seems to be a hard lower limit in the data of around 225,000 salmon

      3. There is a tail towards very high salmon counts (> 500,000 salmon). Tails like this have a significant impact on the mean value and might represent some kind of anamoly in the data.

      4. Overall, the distribution is not real well fit by a bell curve but the median value of 340,000 is similar to the mean so we can use our principles of dispersion to calculate significant differences.

    There has been some speculation and data that suggest there has been a decline of salmon recently in the Columbia River System. What do these data say.?

    Here is the distribution of the data with the last 5 years subtracted out, so there are 39 years worth of data:

    This distribution, defined by 39 points, has a mean of 368,000 salmon with a dispersion of 81,000 salmon and a mean error of 13,000.

    Note: The dispersion for the 39 year sample and the 44 year sample are similar this indicates that we have enough data to accurately determine the dispersion.

    Over the last 5 years, the data are defined by an average of 278,000 salmon with a dispersion of 33,000 and a mean error of 15,000 = (33,000/(sqrt of 5)). Does this data show a significant decline of salmon?

    Since the mean errors are similar we can use (M1-M2)/1.5E1 for an approximation:

    • M1-M2 = 368,000 - 278,000 = 90,000
    • 1.5E1 = 1.5*13,000 = 20,000

    • difference is 90,000/20,000 = 4.5 dispersion units HIGHLY SIGNIFICANT!

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