Opportunistic use of estuarine habitat by juvenile bull trout, Salvelinus confluentus, from the Elwha River before, during, and after dam removal
Estuaries are used by anadromous fishes, either as the definitive marine habitat or as transition habitat as they move to fully marine waters, and extent of estuary use may vary with habitat conditions and fish attributes. Bull trout (Salvelinus confluentus) are commonly fluvial or adfluvial, though anadromous populations also exist. However, little is known about estuary use, especially by juveniles of this threatened species. We sampled the estuaries of the Elwha River, where a spawning population exists, and the nearby Salt Creek, where none exists, to reveal seasonal timing of estuarine use by juvenile bull trout, size of those using the estuary, and possible use of the non-natal estuary. We captured juvenile bull trout (all ≥100 mm FL, most <300 mm) in the Elwha River estuary in all months except August, but primarily December through May. None was captured in Salt Creek’s estuary despite comparable sampling effort. We also evaluated how dam removal on the Elwha River influenced bull trout estuarine occupancy by sampling before, during, and after dam removal, because this process enlarged the estuary but also increased turbidity and sediment transport in the lower river. Catches were low before dam removal, increased during and immediately after removal, and returned to low levels in recent years, suggesting that juveniles temporarily sought refuge from conditions associated with dam removal. Our findings indicate juvenile bull trout occupy estuarine habitat opportunistically; this information may aid conservation efforts as anadromous populations occur elsewhere in rivers with estuaries altered by human development.
KeywordsJuvenile bull trout Estuary Timing Dam removal Elwha River
We thank the many individuals that helped in sampling, including Marisa Christopher, Joshua Davis, David Harvey, Tony Thompson, Seren Weber, Mike Mille, Sheri Washington, Lauren Kerr, Tara McBride, Jamie Michel, Ellie Stevenson, Chris Byrnes, Dave Parks and many volunteers: John Anderson, Normandie Anderson, Catherine Austin, Dave Christian, Elizabeth Christian, and Washington Conservation Corps crew Pete Allen, Nate Indresano, Samantha Miller, and Allie Vitello. We also acknowledge our collaborators Francis Juanes, Bruce Hattendorf, Dwight Barry, Jack Ganzhorn, Barb Blackie, and Nancy Bluestien-Johnson. The Elwha dam removal project occurred due to the tenacity of the members and staff of the Lower Elwha Klallam Tribe, including Rob Elofson and Russ Bush, as well as Brian Winter and local and national staff of the National Park Service and Olympic National Park.
This work was funded by the United States Environmental Protection Agency under assistance agreement PC00J29801 to Washington Department of Fish and Wildlife, the Coastal Watershed Institute, Patagonia, the Olympic Peninsula Surfrider Foundation, the Rose Foundation, the Seattle Foundation, the Hayes Foundation, the Puget Soundkeeper Alliance, the Clallam Marine Resources Committee, the University of Victoria, and the University of Washington. Participation by AL and TQ was supported by the Washington Sea Grant program, University of Washington, pursuant to National Oceanic and Atmospheric Administration Award No. NA10OAR4170075, Project R/LME-7, and also by the H. Mason Keeler and the Richard and Lois Worthington endowments at the University of Washington.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable national and institutional guidelines for the care and use of animals were followed.
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