Landscape Structure and Scale Constraints on Restoring Estuarine Wetlands for Pacific Coast Juvenile Fishes

Abstract

Juveniles of many Pacific Northwest coastal fishes and particularly anadromous species, utilise coastal marshes as “nursery” habitats, predicating the assumption that restoration of marsh sites will promote increased fish survival and production. However, species such as anadromous salmonids have evolved life history strategies that to various degrees depend upon the structure and scale of the estuarine landscape rather than habitat sites per se. Examples include: 1) migration of juvenile salmon among interconnected wetlands along estuarine gradient, 2) their access to dendritic tidal channels, and 3) extended residence in tidal freshwater sloughs. Unfortunately, estuarine habitat restoration is seldom designed or implemented with landscape structure and scale in mind, ignoring important landscape attributes and processes such as habitat matrix heterogeneity, dendritic tidal channel complexity, allometric relationships of estuarine sloughs, and disturbance frequency and intensity. In this analysis, we draw on several estuarine wetland mitigation and restoration sites in the Pacific Northwest to explore the effect of estuarine landscape structure and scale on their effectiveness for protecting and rehabilitating coastal fisheries resources. We argue that basing restoration solely on site-specific criteria may be significantly inhibiting our ability to re-establish estuarine support function for fisheries resources. To significantly recover the function of juvenile fish migration and survival in coastal ecosystems, future marsh restoration must be conceptualized, designed, constructed and assessed taking into account estuarine landscape structure and scale.