Willot 2004

Hydrobiologia (2009) 636:179–190 DOI 10.1007/s10750-009-9947-x

PRIMARY RESEARCH PAPER

Fish habitat use response to anthropogenic induced changes of physical processes in the Elwha estuary, Washington, USA
J. Anne Shaffer • M. Beirne • T. Ritchie R. Paradis • D. Barry • P. Crain
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Received: 5 February 2009 / Revised: 2 September 2009 / Accepted: 11 September 2009 / Published online: 19October 2009 Ó Springer Science+Business Media B.V. 2009

Abstract The Elwha River estuary has been significantly influenced by anthropogenic changes to the river, including two large dams upriver and rock dikes installed in the estuary. Together these have disrupted hydrodynamic processes and subsequent sediment delivery throughout the watershed. This article defines the functional response offish distribution within the estuary as a result of these changes.

Handling editor: Pierluigi Viaroli J. A. Shaffer (&) Á T. Ritchie Washington Department of Fish and Wildlife, 332 E. 5th Street, Port Angeles, WA 98362, USA e-mail: anne.shaffer@dfw.wa.gov M. Beirne Lower Elwha Klallam Tribe, Fish Hatchery Road, Port Angeles, WA 98362, USA e-mail: matt.beirne@elwha.nsn.us R. Paradis Á D. BarryWestern Washington University, Huxley College of the Environment, Port Angeles, WA 98362, USA e-mail: Rebecca@clallambroadband.com D. Barry e-mail: dwight.barry@wwu.edu P. Crain Olympic National Park, 600 Park Avenue, Port Angeles, WA 98362, USA e-mail: Patrick_crain@nps.gov

We assessed fish distribution of three main areas of the Elwha estuary using standard beach seining techniques from March toAugust 2007. Species composition, ecological indices, and relative proportion of all salmonids, and in particular Chinook salmon (Oncorhynchus tshawytscha), were consistently significantly different across the estuary. Differences corresponded to a rock dike installed 30 years ago, and a sediment lens that was observed to form at the entrance to the east estuary. Sediment lenses are documented to be acommon occurrence in the Elwha nearshore, and symptomatic of documented, severely disrupted sediment processes of the Elwha River. Combining the fish distribution documented in this study with the rock dike and observed sediment lens and the sediment processes documented by other researchers we, therefore, conclude: (1) Fish use within the Elwha River estuary is complex, and even fragments ofconnected estuary are critically important for migrating salmon; (2) Anthropogenic effects, including in river damming and diking of the estuary, can be an important ecological driver in nearshore habitat function that should be appropriately considered in estuary habitat research, management, and restoration; and (3) Juvenile salmonids appear to be able to respond to dynamic sediment environments ifthere are habitat options available. Keywords Nearshore Á Estuary Á Sediment Á Hydrodynamics Á Salmon Á Chinook Á Elwha Á Habitat

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Hydrobiologia (2009) 636:179–190

Introduction Hydrodynamic processes, including channel morphology and sediment delivery, define estuarine habitat form (Marshall & Elliot, 1998; Williams et al., 2002). Hydrodynamic processes can result in significantimpacts to habitat function and fish population dynamics. For example, Gregory (1993) and Gregory & Levings (1998) found that turbidity defined predation success by juvenile Chinook in the Fraser River, and Hood (2002) documented the importance of hydrodynamic flow in habitat utilization in estuaries. Sediment delivery is another component of estuarine hydrodynamics that forms nearshore habitats.Although an important component of estuarine hydrodynamics, less is known about the role that sediment delivery plays in estuarine habitat function for fish. Similarly, human alterations, including diking and filling of nearshore environments, can significantly disrupt hydrodynamic processes and, as a result, habitat function (Hood, 2004; Toft et al., 2007). Located on the north Olympic Peninsula in...