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DRAFT 



estimate of the relative impact on the total production of salmonids. This method 

 ignores compensatory survival mechanisms, widely recognized as being important to 

 the population dynamics of most species. To estimate the biological impact of each 

 factor on salmonid production, the matrix method would require a mechanism to sum 

 impact levels while recognizing that increased mortality at one phase of the life cycle 

 can be compensated by reduced mortality at a subsequent stage. The total impact of a 

 given factor on the productivity of the population should be represented by the relative 

 change in the production of adult salmonids. For example, reduced spawning 

 escapement will result in a lower production of juveniles, but if freshwater habitat is 

 not limited the survival of these juveniles to the smolt stage will be increased because 

 of reduced density-dependent mortality (a compensatory mechanism). The net effect 

 on the total production of adults will be less than the direct reduction in juvenile 

 numbers due to this compensation in survival rates. 



(5) The method could not measure the effects of multiple factors 



The matrix methodology could not measure the cumulative impact of multiple factors 

 affecting a population simultaneously. The analysis was limited to an evaluation of the 

 effect of a single factor on one aspect of salmonid life history, and failed to include a 

 method to recognize synergistic interactions of multiple factors on total stock 

 productivity. For example, the effects of a 60 percent harvest rate on coho salmon 

 populations will vary markedly if ocean survival rates (smolt to adult) the previous year 

 change from 8 percent to 4 percent. In addition, a particular harvest rate that is 

 acceptable for a population living in a pristine basin will be unacceptably high if egg to 

 smolt survival rates are reduced because of freshwater habitat degradation. Ignoring 

 these complex relationships results in over-simplified conclusions that are not likely to 

 accurately predict the relative importance of the factors. 



ALTERNATIVE ANALYSIS APPROACH 



To demonstrate the complexity of quantifying and evaluating the effects of various 

 factors on salmonid production in a scientifically valid manner, the Department has 

 developed an example of an alternative matrix approach. This approach is based upon 

 a prediction of the relative change in adult salmonid production due to a variety of 

 factors, and is consistent with concepts currently being used in life cycle modeling to 

 weight the effects of various mortality sources on salmonid production in the Columbia 

 River Basin. A major difference between this approach and the OFIC report matrix is 

 that the relative importance of a factor, or combination of factors, is based upon the 

 predicted change in total adult production of a species. 



In this example, an array of biological impacts is evaluated by estimating changes in 

 five population parameters: (1) adult spawners, (2) fecundity per adult, (3) egg 

 survival, (4) juvenile survival, and (5) survival to adult. Each of these parameters 

 could be ftirther partitioned: for example, juvenile survival could be subdivided into fry 

 survival, summer survival, over-winter survival, etc. The potential causes of biological 

 impact affecting these population parameters are numerous and include such sources as 

 sedimentation, increased stream temperature, predation and harvest. In our example, 

 these causes are generically referred to by a numerical designation (Table 1). 

 Associated with each cause of biological impact is a list of factors or activities that 

 contribute to the identified impact. These factors would include the environmental and 



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