The biological conclusions are based on the 6 hypotheses from which the program has been built around. We found 4 of these hypotheses to need further consideration.
Hypothesis 1. The number of returning adults is a function of survival of juvenile salmon and steelhead during migration in fresh water.
Figure 18. Type III survivorship curve.
- A weak correlation (R2 =.27) between the numbers of juveniles out migrating and adults returning to freshwater shows other factors may be at play.
- Possible causes are varying ocean and meteorological conditions (Koslow et al. 2002) or effects common in species experiencing type III survivorship curves (Figure 11 on right).
Hypothesis 2. Northern pikeminnow in the main-stem Columbia and Snake River reservoirs consume significant numbers of juvenile salmon and steelhead that would otherwise have survived migration.
Figure 19. Double-crested Cormorants feeding.
- Pikeminnow predation varies both by season and among areas throughout the Columbia River basin (Petersen 1994).
- Recent data showsthe potential for reduced predation rates by pikeminnow with only 8% of sampled fish stomach contents consisting of salmonids (Porter 2010).
- Evidence has been found suggesting that there is increased predation when the juvenile salmonids reach the estuaries (Roby and Collis 2010). Double-crested Cormorant predation could be compensating for reduced pikeminnow predation levels.
Hypothesis 4. The cumulative effect of a 10 - 20% annual exploitation rate reduces
the predation rate from northern pikeminnow by 50% by reducing the
population of older piscivorous individuals.
Figure 20. Northern pikeminnow caught for the program.
- The 20% exploitation rate of northern pikeminnow is
confidence interval go past the 20% goal.
- Effects of pikeminnow removal may be an overestimate based on Porters 2010 findings of the small percentage of salmonids in the pikeminnow diet. Porter found that only 8%
percentage to be around 78% (Rieman et al. 1991)
Hypothesis 6. Northern pikeminnow population dynamics (i.e., factors regulating population size) or the composition of the resident fish community do not compensate for removals.
- Lack of data on historical pikeminnow growth and population dynamcis prevent a full analysis of the shift in age class structure during the implementation of the program.
- Further analysis of other sources of predation and loss throughout the basin are needed to evaluate potential compensatory loss due to changing numbers and diets of other species present.
The evaluation of the economic basis of the program is dependent upon the number of returning adults as a product of increased juvenile survival.
- Annual jobs created by the program from 2005 to 2007 were 45,463 (The Research Group 2009).
- A $15 deficit was found per adult salmon based on market cost, but the number of harvested salmon is unknown.
- The cultural value of salmonids in the Columbia River basin is unknown. This intrinsic value of salmonids play an important roll in determining the overall economic worth of the program.
Figure 22. Collection of removed pikeminnow.
- Ethics of the program differ from different species perspectives. Removal of one native
- Immediate closure of the program would be unethical to humans because of its popularity and the economic value to the community.
- Eventual discontinuation of the program is the most appropriate step to take because of
Figure 23. School of juvenile Chinook Salmon.
- Conduct new evaluation of pikeminnow predation levels on salmonids
- Observe potential compensatory predation by avian predators (Caspian Terns and Double-crested Cormorants)
- Continue work to improve out migration passage for juvenile salmonids at dams
- Transition to alternative energy sources
The future focus for salmonid recovery should be focused on helping adult stage fish survive to spawning because of the difficulties experience by type III survivorship curves. This can be done through a number of methods.
Figure 24. Spawning Chinook Salmon
- Improve dam passage for returning adult salmonids
- Improve water quality of riverways
- Improve hazing techniques of pinnepeds
- Reduce adult salmonid harvest quotas to levels that would sustain salmonid population growth.