White Paper - Overwater Structures: Marine Issues

As part of the process outlined in Washington's Statewide Strategy to Recover Salmon: Extinction is Not an Option the Washington Departments of Fish and Wildlife, Ecology, and Transportation were charged to develop Aquatic Habitat Guidelines employing an integrated approach to marine, freshwater, and riparian habitat protection and restoration. Guidelines will be issued, as funding allows, in a series of manuals addressing many aspects of aquatic and riparian habitat protection and restoration.

This document is one of a series of white papers developed to provide a legitimate scientific and technical basis for developing Aquatic Habitat Guidelines. The white papers address the current understanding of impacts of development and land management activities on aquatic habitat, and potential mitigation for these impacts. Individual white papers will not necessarily result in a corresponding guidance document. Instead, guidance document development, addressing management and technical assistance needs, may incorporate information synthesized from one or more of the white papers.

The scope of work for each white paper requested a �"comprehensive but not exhaustive” review of the peer-reviewed scientific literature, symposia literature, and technical (gray) literature, with an emphasis on the peer-reviewed literature. The reader of this report can therefore expect a broad review of the literature, which is current through late 2000. Several of the white papers also contain similar elements including the following sections: overview of the guidelines project, overview of the subject white paper, assessment of the state of knowledge, summary of existing guidance, recommendations for future guidance documents, glossary of technical terms, and bibliography.

This paper synthesizes the extent and nature of scientific information about how overwater structures and associated activities potentially affect habitats and key ecological functions that support recruitment and sustainability of estuarine and marine fauna in Washington State. The mechanisms of potential overwater structure effects are characterized as alterations to ambient light and alterations to wave energy and substrate regimes.

Regional findings pertaining to such overwater structure effects to these ecosystem regimes are presented and discussed. We also identify and discuss both direct and cumulative effects to natural shorelines and urban industrialized shorelines and present measures to mitigate and control for direct and cumulative impacts. Existing scientific gaps and recommendations for future exploration are presented along with an overview of the existing regulatory framework pertaining to overwater structures.

Prey resource production, refugia, and reproduction are key ecological functions provided by shallow nearshore habitats. These functions are important to the recruitment and survival of the region's fish and shellfish species. Overwater structures and associated activities can impact the ecological functions of habitat through the alteration of those controlling factors that support key ecological functions such as spawning, rearing, and refugia. Whether any of these impacts occur and to what degree they occur at any one site depend upon the nature of site-specific factors and the type, characteristics, and use patterns of the overwater structure located at a specific site. Over the past 25 years, many studies have identified these impacts. Often these studies have been focused upon particular species of concern such as juvenile salmonids and Dungeness crab. This paper broadens the species of concern to include representative fish and shellfish species with a dependence upon the region's nearshore marine ecosystems. Those species represented in this paper include a wide variety of ecologically important and vulnerable species known to utilize nearshore habitats during different life-history stages. For most species, juvenile stages have an important dependency, albeit at different magnitudes, upon nearshore marine and estuarine ecosystems. This paper presents an overview of such animal dependencies upon specific habitat characteristics, the controlling factors determining habitat characteristics, and information sources pertaining to known and potential effects posed by various forms of overwater structures. The description of habitat impacts are limited to those occurring within those ecosystems located between the tidal levels of mean high water spring (MHWS) and -15 meters below mean lower low water (MLLW). Descriptions and definitions of these intertidal and shallow subtidal ecosystems are also included.