121-30 Geomorphic Habitat Type, Drift Cell, Forage Fish, and Juvenile Salmon: Are They Linked?
Abstract
In this study we address the role of geomorphic habitat type and drift cell in defining fish use of nearshore habitats, as well as the role environmental degradation may play in habitat function at the drift cell scale. Key areas of nearshore central and western Strait of Juan de Fuca were categorized by geomorphic habitat type and then assessed for fish presence over a year period. The study was structured to assess fish use of habitat type both within a degraded drift cell (Elwha drift cell) and intact comparative areas. A subset of fish were also sampled for genetic analysis. Key findings from this include: 1. Ecological function of the nearshore is complex, with very strong seasonal variation both within and across geomorphic habitat type; 2. Geomorphic habitat types of the nearshore function differently depending on the habitat type, time of year, and species. Fish life history and month also are important drivers in function of geomorphic nearshore habitat. For example, forage fish (smelt, sand lance, and herring) which were the most abundant fish of this study, seasonally used embayed, spit, and bluff shorelines much more heavily than lower rivers. Juvenile Chinook, coho, and chum salmon seasonally used all geomorphic habitat types but at much lower densities; 3.When geomorphic habitats types were combined and analyzed at the drift cell scale, the impaired drift cell functioned lower ecologically than the intact drift cell, and; 4) Genetic analysis results of a subset of Chinook and coho revealed fish from as far away as the Columbia River utilizing central Strait of Juan de Fuca shorelines. These results strongly support the importance of scale in defining ecological health and function, the cross regional importance of coastal nearshore environments for migrating salmon (and possibly forage fish) and the need for additional, more detailed study of both of these components of nearshore function.
In this study we address the role of geomorphic habitat type and drift cell in defining fish use of nearshore habitats, as well as the role environmental degradation may play in habitat function at the drift cell scale. Key areas of nearshore central and western Strait of Juan de Fuca were categorized by geomorphic habitat type and then assessed for fish presence over a year period. The study was structured to assess fish use of habitat type both within a degraded drift cell (Elwha drift cell) and intact comparative areas. A subset of fish were also sampled for genetic analysis. Key findings from this include: 1. Ecological function of the nearshore is complex, with very strong seasonal variation both within and across geomorphic habitat type; 2. Geomorphic habitat types of the nearshore function differently depending on the habitat type, time of year, and species. Fish life history and month also are important drivers in function of geomorphic nearshore habitat. For example, forage fish (smelt, sand lance, and herring) which were the most abundant fish of this study, seasonally used embayed, spit, and bluff shorelines much more heavily than lower rivers. Juvenile Chinook, coho, and chum salmon seasonally used all geomorphic habitat types but at much lower densities; 3.When geomorphic habitats types were combined and analyzed at the drift cell scale, the impaired drift cell functioned lower ecologically than the intact drift cell, and; 4) Genetic analysis results of a subset of Chinook and coho revealed fish from as far away as the Columbia River utilizing central Strait of Juan de Fuca shorelines. These results strongly support the importance of scale in defining ecological health and function, the cross regional importance of coastal nearshore environments for migrating salmon (and possibly forage fish) and the need for additional, more detailed study of both of these components of nearshore function.
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