3.4 Summary Conclusions and Recommendations |
Although Bainbridge Island is generally considered semi-rural, over 82% of shoreline parcels are developed to densities only second to the Islands urban centers, and 52% of the shoreline is armored or otherwise modified. Its nearshore ecosystems provide support for a vast number of marine plants and animals and are vital to sustaining endangered species such as salmon, although in many cases these biological functions remain unquantified. The present report outlines a science-based framework for assessing the status of nearshore ecological conditions on Bainbridge Island.
This assessment is intended as a screening tool for prioritizing management actions Island-wide, and should be considered a living document that can be continuously refined as our knowledge base increases. The assessment framework is comprised of the following components:
- A conceptual model that is based on the best available science for the nearshore ecosystem. This model organizes the linkages between human impacts/actions, controlling factors, habitat structure, and ecological functions.
- Two ecologically- relevant spatial scales: reach and management area;
- Geomorphic context at the reach level;
- A scoring system based on the status of nine controlling factors metrics;
- An attempt to validate the scoring with limited existing data on ecological functions.
Key findings of the nearshore assessment were as follows:
- Bainbridge Island’s shoreline represents a microcosm of what is generally found in Puget Sound, with moderate levels of impacts to nearshore resources, but extreme examples of high and low impacts as well. Most management areas were considered moderately impacted by human activities.
- Of nine MAs on Bainbridge Island, only Eagle Harbor (MA-5) was considered highly impacted; this MA included some of the most highly disturbed reaches found around the Island. Two MAs stood out as relatively undisturbed or least impacted: Murden Cove (MA-4) and Blakely Harbor (MA-6).
- At a reach level, assessment scoring did identify some stretches of shoreline commonly acknowledged as highly impacted or modified by human actions (e.g., reaches associated with the Wyckoff Superfund site on Bill Point and below feeder bluffs in Rolling Bay), as well as the more pristine reaches with minimal human impacts.
- The substrate type and depth/slope metrics represented the most impacted controlling factors over the entire Island. Low (poor) scores in these metrics suggest that high rates of shoreline armoring, armoring encroachment, and point modifications have significantly changed the historic composition of substrate and depth-slope contours along Bainbridge Island shorelines. Impacts to these controlling factors have likely caused significant affects to the nearshore ecosystem. Most nearshore organisms and habitats assemblages are dependent on specific substrate characteristics (e.g. rocky or sandy) and are limited to particular tidal elevations due to light availability and sensitivity to exposure out of water. Changes in substrate type or depth/slope may have caused habitat shifts or reduced the available area suitable for the formation of habitats and the processes necessary to sustain habitats.
- The hydrology and physical disturbance metrics represented the least-impacted controlling factors Island-wide. The relatively higher (better) scores in these metrics suggest that low-to-moderate intensity residential land use (as opposed to high-intensity urban or industrial land use) along many of the Island’s shorelines has likely helped keep impacts to hydrology low and limited physical disturbances. These controlling factors can be sustained by maintaining forested marine riparian zones as well as avoiding and reducing intertidal/subtidal fill, tidal constrictions, and encroaching armoring. The discharge of untreated stormwater should be avoided and reduced. Floats, boats and mooring buoys should be located in deep water where they will not ground. Boats and boating facilities, including docks, buoys, and boat ramps, should be located to avoid and operated to minimize impacts to kelp, eelgrass, and other sensitive habitats.
- Scoring of some cumulative landscape (MA) controlling factor metrics might be improved in future updates of the assessment. For example, average cumulative MA scores associated with the natural shade metric were sometimes negatively associated with conditions at the landscape scale. High (good) scores were observed in MAs with a low total percentage of overhanging riparian vegetation along shorelines, and vice-versa. This discrepancy can largely be attributed to geomorphic factors (i.e., natural shade was not considered an issue in exposed beach/backshore/spit habitats) but may also indicate a weakness in the method for calculating cumulative landscape (MA) assessment scores. Refining the methods used to calculate cumulative landscape (MA) assessment scores (such as including reach length as a means of standardization) and to characterize the cumulative landscape (MA) assessment scoring (such as using median and highest/lowest quartiles) could improve the accuracy of cumulative landscape (MA) assessment results.
- Scoring of some ecological function might be improved in future updates of the assessment. Scores of documented ecological functions were highest (best) in the northern portions of Bainbridge Island, including Manzanita Bay (MA-9), Agate Passage (MA-1), and Port Madison Bay (MA-2). In contrast, the lowest (worst) EF scores were observed in Eagle Harbor (MA-5), Blakely Harbor (MA-6), and Rich Passage (MA-7). However, these scores were highly influenced by the presence of forage fish spawning habitats, one of the few ecological functions that has not been thoroughly and consistently quantified across all reaches, therefore possibly depressing scores where spawning has not yet been evaluated. Predictive mapping of spawning substrate based on sediment characteristics may prove a useful intermediate tool to assess forage fish metrics until field surveys are conducted. EF scoring might be further refined in future updates of the assessment, with distinctions drawn based on geomorphic context, similar to how CF scores where modified in this assessment.
- Preliminary validation efforts suggest that low (poor) controlling factors scores are often correlated with reduced habitat diversity and other indicators of ecological function (e.g., forage-fish spawning), especially in some geomorphic settings. Closer examination of outliers may assist in refining assessment techniques and selecting a more appropriate suite of parameters for monitoring.
The current assessment methodology primarily focuses on aquatic habitats and functions. Future updates to the assessment should add focus to backshore and marine riparian habitats and functions.
Improved mapping of feeder bluffs and other sediment sources should be conducted. - In general, the assessment appeared to offer the right balance of detail and consistency when used as the first step in a screening process for management options.
Appendix E outlines management strategies that are appropriate for Bainbridge Island nearshore habitats, based on the following points:
- Management strategies are applied, in part, based on geomorphic conditions at the reach (site) and management area (landscape) levels. Five fundamental strategies for improving ecosystem functions of nearshore systems include habitat creation, enhancement, restoration, conservation, and preservation.
Landscape ecology considerations were included in defining management strategies. Management strategy recommendations are assigned according to the level of disturbance at both the management area and reach scales (Figure B-14). If damages are great at both scales, fewer management strategies are likely to be successful. Conversely, if damage is relatively low on both scales, there is a broader array of management options. For example, it would make little sense to restore the ecosystem at a heavily damaged nearshore site (reach) if the landscape (management area) upon which this site depends is also heavily damaged. A more appropriate strategy would be restoration or enhancement of selected attributes of the reach. - To better refine management actions for a particular site (reach or portion of a reach), eight criteria can be used to enhance ecosystem structure and function based on landscape ecology and restoration ecology principles. The criteria include site size, habitat complexity, accessibility, connectance, potential to conform to natural conditions, potential for self-maintenance, potential benefit to nearshore dependent threatened and endangered species, and potential to improve ecosystem functions (e.g., forage fish spawning areas) within a particular reach or management area.
The assessment and prioritization framework will be most effective when it involves the local expertise of scientists and resource managers who are familiar with the Bainbridge Island shoreline and its ecological resources.
Assessing the results of management actions requires a monitoring program (Appendix F), which will assist in determining not only whether the actions are successful, but how to adaptively modify or adjust management actions to make them more successful. Other key points that are discussed and considered in the monitoring recommendations include:
- Consideration of monitoring goals, scale (effort in time and space), timing, sampling design and replication, reference site designation, attribute selection, sampling methods, and costs.
- Focus on monitoring that provides data for key attributes within the conceptual framework. In this way, monitoring will link processes to the nearshore habitat structure, integrate a multitude of nearshore habitats that support a variety of functions, establish relationships between structure and function, and ultimately can scale local processes to the broader Puget Sound ecosystem. Suggested key monitoring attributes include: controlling factors (e.g., water quality, sediment processes, shoreline modifications), habitat structure (e.g., land use-land cover assessment, nearshore riparian cover, shallow water aquatic habitats), and ecological functions (e.g., fish assemblages, exotic species).
- To opportunistically fulfill a range of monitoring goals using rigorous methods under the limited resources (both funding and personnel) available at a local level, we recommend: 1) selectively monitoring several key nearshore parameters; 2) focusing monitoring efforts at ongoing local monitoring and assessment activities; 3) using consistent and standardized protocols; 4) forging partnerships and involving other stakeholders; and 5) leveraging opportunities with existing resources unique to Bainbridge Island.
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