Large Wood and Instream Habitat for Juvenile Coho Salmon and Larval Lampreys in a Pacific Northwest Stream

Abstract

The influences of large wood on Pacific salmon are well‐studied, but such studies on nonsalmonid species such as lampreys are uncommon. To address this need, we evaluated the potential effects of large wood on larval lampreys (Pacific Lamprey Entosphenus tridentatus and potentially Western Brook Lamprey Lampetra richardsoni) as well as on juvenile Coho Salmon Oncorhynchus kisutch in a small, coastal, Oregon stream. Our objectives were to (1) identify instream habitat characteristics associated with the presence of larval lampreys and abundance of juvenile Coho Salmon and (2) evaluate how these characteristics were associated with instream wood. To address habitat use, we quantified presence of larval lampreys in 92 pools and abundance of juvenile Coho Salmon in 44 pools during summer low flows. We focused on a study reach where large wood was introduced into the stream between 2008 and 2009. Results indicated that presence of larval lampreys was significantly associated with the availability of fine sediment and deeper substrate. The abundance of juvenile Coho Salmon (fish per pool) was strongly associated with pool surface area and to a weaker extent with the proportion of cobble and boulder substrates in pools. Pools with wood, regardless of whether they were formed by wood, had significantly greater coverage of fine sediment, deeper substrate, and greater pool surface area. Taken together, these results suggest that instream wood can provide habitat associated with the presence of larval lampreys and greater abundance of juvenile Coho Salmon. Received September 11, 2016; accepted March 25, 2017 Published online May 31, 2017

Evaluating Coexistence of Fish Species with Coastal Cutthroat Trout in Low Order Streams of Western Oregon and Washington, USA

“…Larger coastal cutthroat trout in smaller streams (similar in size to those considered herein) have been observed to be more closely associated with larger, deeper locations, or locations with available instream cover [30][31][32]. In this study there was some evidence that increasing body size of coastal cutthroat trout was associated with decreased density of coho salmon, a response that could be mediated by physical conditions that influence density of larger coastal cutthroat trout [33].…”

“…Considering the difficulty of implementing controlled experiments and the complexity of potential interactions through the life cycle, as well as their transferability to field conditions [43], we do not envision clear resolution of species interactions in the near future. For example, the potential influences of natural size asymmetries between juveniles of earlier emerging coho salmon and later-emerging coastal cutthroat trout [41,42] could be reduced if larger resident coastal cutthroat trout also prey on juvenile coho salmon [33,44,45].…”

River Network and Reach‐Scale Controls on Habitat for Lamprey Larvae in the Umpqua River Basin, Oregon

“…Instead, these results reinforce the importance of the influence of local geomorphic processes on habitat heterogeneity (in the form of high‐flow channels, bars, and undercut banks) and PBH. Native lampreys will likely benefit from conservation strategies that increase habitat heterogeneity (Schultz et al 2016; Gonzalez et al 2017).…”

“…Lamprey larvae were found at the upper Little Wolf and two Slide Creek reaches, which had channel slopes measured in the field that were less than 0.016 (Table 3). Nearly 60% of the lamprey larvae in the upper Little Wolf Creek reach were found in a large wood jam upstream of a high-flow channel and large bar ( Figure 7A, transects 8-10; see also Gonzalez et al 2017). About 50% of the lamprey larvae in the lower Slide Creek reach were in a pool with undercut banks and large wood ( Figure 7D, transects 2-3).…”

“…Instead, these results reinforce the importance of the influence of local geomorphic processes on habitat heterogeneity (in the form of high-flow channels, bars, and undercut banks) and PBH. Native lampreys will likely benefit from conservation strategies that increase habitat heterogeneity (Schultz et al 2016;Gonzalez et al 2017). Reach-scale channel characteristics can also prevent the formation of fine sediment deposits for burrowing by influencing local transport capacity conditions, as illustrated by the lower Little Wolf Creek reach.…”