Juvenile Salmon Response to the Placement of Engineered Log Jams (Eljs) in the Elwha River, Washington State, Usa

Abstract

Engineered log jams (ELJs) are increasingly being used in large rivers to create fish habitat and as an alternative to riprap for bank stabilization. However, there have been few studies that have systematically examined how juvenile salmonids utilized these structures relative to other available habitat. We examined Chinook salmon (Oncorhynchus tshawytscha), coho salmon (O. kisutch) and trout (O. mykiss and O. clarki) response to the placement of engineered log jams (ELJs) in the Elwha River, Washington State, USA. We used summer snorkel surveys and a paired control-treatment design to determine how engineered log jams in a large river system affect the density of juvenile salmon. We hypothesized that densities of juvenile salmonids would be greater in habitats with ELJs than in habitats without ELJs in the Elwha River and that this ELJ effect would vary by species and size class. Juvenile salmonid density was higher in ELJ units for all control-treatment pairs except for one pair in 2002 and one pair in 2003. Positive mean differences in juvenile salmon densities between ELJ and non-ELJ units were observed in two of 4 years for all juvenile salmon, trout greater than 100 mm and juvenile Chinook salmon. Positive mean differences occurred in one of 4 years for juvenile coho salmon and trout less than 100 mm. The results suggest that ELJs are potentially useful for restoring juvenile salmon habitat in the Elwha River, Washington State, USA.

Wood placement in river restoration: fact, fiction, and future direction

“…As early as the 1930s, Tarzwell (1937) called for more rigorous monitoring and evaluation to determine physical and biological effectiveness. Since then, many studies have reported improved habitat and fish production, particularly for salmonid fishes (e.g., Binns 1999;Hunt 1976;Pess et al 2012;Roni and Quinn 2001a;Shetter et al 1949; for a review, see Roni et al 2008), whereas others have reported no detectable changes (e.g., Chapman 1996;Rosi-Marshall et al 2006;Stewart et al 2009;Thompson 2006).…”

Does variable channel morphology lead to dynamic salmon habitat?

“…Freshwater habitat is important to Pacific salmonid species as some spend one or more years rearing in river systems as juveniles (Meehan and Bjornn, 1991). Structural cover elements in stream channels, such as in-stream large wood (LW), also serve an important role in sheltering juveniles from predation and in reducing water velocities (Bjornn and Reiser, 1991;Hafs et al, 2014) such that LW quantities are often positively associated with juvenile salmonid abundance (Cederholm et al, 1997;Benke and Wallace, 2003;Pess et al, 2012). Metabolic efficiency and growth rate depends on stream temperature and availability of food sources (Becker and Genoway, 1979;Murphy and Meehan, 1991), in addition to dissolved oxygen and turbidity levels (Bjornn and Reiser, 1991).…”

Does River Restoration Increase Fish Abundance and Survival or Concentrate Fish? The Effects of Project Scale, Location, and Fish Life History

“…Pess et al. () hypothesized that the density of juvenile salmonids in habitat units with engineered logjams decreased as the number of logjams in their study reach increased from 8 to 19 during 2000–2003. This suggests either that juvenile abundance was at carrying capacity before the placement of additional logjams or that fish had not yet fully responded to the placement of logjams that were added during the study period.…”