2.2.5 Validating Assessment Scores |
A preliminary exercise was conducted to validate the assessment scores by evaluating existing ecological functions at the reach level with a simple index of ten potential indicators (listed below), including presence of vegetative habitats, and invertebrate and vertebrate species.
- Proximity to salmon-bearing stream
- Herring spawning area
- Surf smelt spawning beach
- Pacific sandlance spawning beach
- Geoduck beds
- Eelgrass bed (Zostera spp.)
- Salt marsh (Salicornia, Triglochin, Deschampsia, Distichlis)
- Bull kelp (Nereocystis)
- Intertidal seaweed (Fucus, Laminaria, Sargassum, Ulva)
- Overhanging riparian vegetation
As with the controlling factor assessment, the scoring approach uses a five-point scale to assign qualitative categories of each ecological function metric within each reach, with 1 representing “not present,” 2 through 4 representing “intermediate function” (e.g., patchy habitat distribution or close proximity to some documented functions), and 5 representing “documented functions” or “continuous habitat distribution” (Table 7). The cumulative ecological function (EF) score is additive and computed as the sum of all metric scores in each reach. Therefore, the index assumes that higher ecological functions are present in reaches with a high diversity of habitats and faunal groups. Average reach scores were also computed within each management area and across all of Bainbridge Island to make comparisons at a broader landscape scale.
Scoring criteria for each metric is described below and in Table 6, with data sources summarized in Table 3. For the salmon-bearing stream metric (Haring 2000; May and Peterson 2003), reaches were scored based on proximity to the stream outlet: 1 if more than two reaches away from outlet reach, 2 if two reaches away from outlet reach, 3 if one reach away from outlet reach, 4 if adjacent to outlet reach, and 5 if outlet reach. For the forage-fish spawning (herring, surf smelt, and sandlance) and geoduck metrics (WDFW 2001), reaches were scored based on presence or absence of these resources using two categories: 1 if not present; 5 if present. For most of the habitat metrics (eelgrass, saltmarsh, bull kelp, and intertidal seaweed) (WDNR 2001), reaches were scored based on the extent of habitat present in the reach using three categories: 1 if not present, 3 if patchy distribution, and 5 if continuous distribution. Finally, the overhanging riparian vegetation metric (COBI 2002, Best 2003) was scored for each reach based on percentage of shoreline coverage using three categories differentiated by equal breaks in the data: 1 if >0 to 33%; 3 if >33% to 66%; and 5 if >66%.
After the ecological function (EF) scores were tabulated, these values were paired with corresponding controlling factor (CF) assessment scores for each reach, graphed in an X-Y plot, and visually examined to discern patterns and relationships (Figures B-72 through B-76). These preliminary results show that the relationships between ecological functions and controlling factors are generally weak, but they do suggest that low (poor) CF scores are generally correlated with reduced habitat diversity and other indicators of ecological function. This appears to be the case in some geomorphic settings more than others. Future refinements to the validation methodology would be desirable, and could include refining the list of potential indicators and modifying the scoring based on geomorphic setting.
It must also be noted, that several of the metrics used did not benefit from comprehensive and geographically complete data sets. For example, herring, surf smelt, and sandlance spawning surveys have not been comprehensive over all of Bainbridge Island. Filling in these data gaps or finding interim surrogates (i.e. suitable spawning substrate) may be important to future refinements of the validation process. Given the limited scale-specific information available at this time, it is emphasized that ecological function scores serve as a rough surrogate for habitat function that can serve both as a tool to validate a more detailed controlling factors assessment, as well as a guide for improving management action prioritization (Appendix E). Ultimately, only ongoing research and monitoring conducted at an appropriate scale can clarify our conceptual understanding of nearshore ecological relationships, which can be used to validate the most appropriate indicators of habitat function (Appendix F).
Table 7. Summary of Ecological Function Scoring
Fish Bearing Stream Proximity Herring Spawning Surf Smelt Spawning Sandlance Spawning Geoducks
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Eelgrass Saltmarsh Bull Kelp Intertidal Seaweed Overhanging Vegetation |
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