NOAA-NMFS-NWFSC TM-35: Chinook Status Review
Appendix F: The Risk Matrix Method
To tie the various risk considerations into an overall assessment of extinction risk for each ESU, the Biological Review Team (BRT) members scored risks in a number of categories using a matrix form (Table F-1). For scoring and reaching an overall conclusion regarding extinction risk for an ESU, the following method was used. 1) After reviewing previous documents and hearing presentations and discussions during the meeting, each BRT member filled in as much of the matrix as possible, scoring the various factors according to the relative degree of risk based on available information. 2) Scores from individual members were tallied on a single sheet, and summarized. 3) The BRT reached an overall conclusion regarding the degree of extinction risk facing each ESU after steps 1 and 2 were completed for all ESUs.
Following is a list of factors considered, along with sub-categories and important questions for each. This is not a complete list, but covers the considerations that have been important in past status reviews. Specific considerations within each of these areas are discussed more fully in the main report.
Questions regarding abundance can be put into three sub-categories:
Small population risks--Is the overall ESU (or discrete populations within the ESU) at such low abundance that small-population risks (random genetic effects, Allee effects, random demographic or environmental effects) are likely to be significant?
Distribution--Do present populations adequately represent historical patterns of geographic distribution and ecological/genetic/life-history diversity? Does fragmentation of previously connected populations pose a risk? Is the ESU at risk in a significant portion of its range?
Habitat capacity--Is abundance limited by current habitat capacity? If so, is current habitat capacity adequate to ensure continued population viability? (Here, only habitat capacity is considered. Habitat quality as it affects trends or productivity is considered in the next section.)
Again, considerations may be divided into three sub-categories:
Population trends--Is the overall ESU (or populations within it) declining in abundance at a rate that risks extinction in the near future? Is variation in population abundance, in combination with average abundance and trends, sufficiently high to cause risk of extinction?
Productivity--Has population productivity declined or is it declining toward the point where populations may not be sustainable? Is there evidence that natural populations are/can be self-sustaining without the infusion of hatchery-reared fish?
Limiting factors--Are there factors (such as poor freshwater or ocean habitat quality, harvest or other human-induced mortality, interactions with other species) that currently limit productivity to the point where populations may not be sustainable? Are such factors expected to continue into the future? Are there natural or anthropogenic factors that have increased variability in reproduction or survival for populations beyond the historic range of environmental variability? Are there factors that have increased the vulnerability of populations to natural levels of environmental variability?
Genetic integrity can be affected through either random effects (included under "Small population risks" above) or directional effects. The major sources of directional effects of concern here are introduced genotypes, interactions with local or non-native hatchery fish, or artificial selection (e.g., through selective harvest or habitat modification). These directional effects pose two major types of risk for natural populations:
Loss of fitness--Has interbreeding or artificial selection reduced fitness of natural populations to the point that this is a significant extinction risk factor?
Loss of diversity--Has there been a substantial loss of diversity within or between populations?
For both types of risk, it may also be important to ask the following question: Even if such interactions are not occurring at present, have past events substantially affected fitness and/or diversity of natural populations within the ESU to the extent that long-term population sustainability is compromised?
Are there other factors that indicate risks to the sustainability of the ESU or component populations? Such factors may include disease prevalence, predation, and changes in life-history characteristics such as spawning age or size.
This category was included to recognize events (natural or human-induced) that have predictable effects on risk for the ESU, but which have occurred too recently to be reflected in abundance, trend, genetic, or other data considered by the BRT. Examples might include recent changes in management (such as harvest rates or hatchery practices), human-induced changes in the environment (habitat degradation or enhancement), or natural events (such as floods or volcanic eruptions). Recent changes in management were considered only where they were already fully or partially implemented and had reasonably predictable consequences.
Risk from individual factors were ranked on a scale of 1 (very low risk) to 5 (high risk):
1) Very Low Risk--Unlikely that this factor contributes significantly to risk of extinction, either by itself or in combination with other factors.
2) Low Risk--Unlikely that this factor contributes significantly to risk of extinction by itself, but some concern that it may in combination with other factors.
3) Moderate Risk--This factor contributes significantly to long-term risk of extinction, but does not in itself constitute a danger of extinction in the near future.
4) Increasing Risk--Present risk is Low or Moderate, but is likely to increase to high risk in the foreseeable future if present conditions continue.
5) High Risk--This factor by itself indicates danger of extinction in the near future.
The "Recent Events" category does not represent specific risk factors, but rather factors that may alter the overall risk score for an ESU from the conclusion based on data available to date. This category was scored as follows: "++" Expect a strong improvement in status of the ESU; "+" Expect some improvement in status; "0" Neutral effect on status; '-' Expect some decline in status; "--" Expect strong decline in status.
The summary score of overall risk uses categories that correspond to definitions in the ESA: in danger of extinction, likely to become endangered in the foreseeable future, or neither. (Note, however, that these scores do not correspond to recommendations for a particular listing action because they are based only on past and present biological condition of the populations and do not contain a complete evaluation of conservation measures as required under the ESA.)
This summary score is not a simple average of the risk factors for individual categories, but rather a judgment of overall risk based on likely interactions among factors. A single factor with a "High Risk" score may be sufficient to result in an overall score of "in danger of extinction," but such an overall score could also result from a combination of several factors with low or moderate risk scores.
While the table has no specific box for scoring level of confidence in risk scores, this can be an important consideration in reaching listing decisions. Concerns about confidence were noted in the "Comments" section.
BRT scores for the three major categories of risk for each chinook salmon ESU are summarized in Table F-2. We do not summarize the "Other Risks" and "Recent Events" categories here, because factors included in these categories varied among ESUs; these factors are discussed in the main report. ESUs for which reviews had previously been completed were not scored.
Table F-1. Example of a blank risk matrix for a single ESU. Each Biological Review Team member filled out scores on one form for each ESU.
Risk Factor |
Comments | Risk |
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Other Risks |
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| Recent Events |
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| Concerns: |
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Table F-2. Summary of main risk categories for the chinook salmon ESUs. Numbers in each cell are the mean score, with range of scores in parentheses. "NS" means "not scored" and applies to ESUs that had been previously evaluated and had no boundary changes.
| ESU | Abundance | Trends/ Productivity/Variability | Genetic Integrity |
| 1) Sacramento Winter Run | NS | NS | NS |
| 2) Central Valley Spring Run | 4.6
(4-5) |
4.2 (4-5) |
3.6 (2-5) |
| 3) Central Valley Fall Run | 3.3 (2-5) |
3.3 (2-5) |
3.3 (2-5) |
| 4) Southern Oregon and California Coasts | 3.7 (2-5) |
3.7 (2-5) |
2.0 (1-3) |
| 5) Upper Klamath and Trinity Rivers | 3.1 (2-5) |
2.4 (1-5) |
2.6 (2-4) |
| 6) Oregon Coast | 1.6 (1-2) |
2.2 (1-4) |
3.5 (2-5) |
| 7) Washington Coast | 2.2 (1-4) |
2.6 (2-4) |
2.6 (1-4) |
| 8) Puget Sound | 3.5 (2-5) |
3.9 (3-5) |
3.6 (2-5) |
| 9) Lower Columbia River | 3.1 (1-4) |
3.3 (2-4) |
3.5 (2-5) |
| 10) Upper Willamette River | 3.6 (2-5) |
3.3 (1-5) |
3.1 (2-5) |
| 11) Middle Columbia River Spring Run | 2.8 (2-5) |
3.1 (2-4) |
2.4 (1-4) |
| 12) Upper Columbia River Summer and Fall Run | NS |
NS | NS |
| 13) Upper Columbia River Spring Run | 4.5 (4-5) | 4.7 (3-5) |
3.3 (2-5) |
| 14) Snake River Fall Run | 3.8 (3-5) |
3.3 (2-5) |
2.9 (2-4) |
| 15) Snake River Spring and Summer Run | NS |
NS | NS |