A Classification of Habitat Types in a Large River and Their Use by Juvenile Salmonids

Abstract

We describe six habitat types for large rivers (>100 m bank‐full width), including pools, riffles, and glides in midchannel and bank edges, bar edges, and backwaters along channel margins. Midchannel units were deeper and faster than edge units on average. Among edge habitat types, backwater units had the lowest velocities and contained complex cover consisting mainly of wood accumulations and aquatic plants. Banks and bars had similar velocity distributions, but banks had more complex cover such as rootwads and debris jams. Because sampling of juvenile salmonids was ineffective in the midchannel units (electrofishing capture efficiency was low, and the units were too deep and fast to snorkel), we focused our sampling efforts on juvenile salmonid use of edge habitats during winter, spring, and late summer. Densities of juvenile Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch were highest in bank and backwater units in winter, whereas age‐0 and age‐1 or older steelhead densities were highest in bank units in winter. In summer, only coho salmon densities were significantly different among edge unit types, densities being highest in banks and backwaters. Microhabitat selection (velocity, depth, and cover type) by juvenile salmonids mirrored that in small streams, most fish occupying areas with a velocity less than 15 cm/s and wood cover. Among ocean‐type salmon, Chinook and chum salmon fry were captured in large numbers in all edge units and exhibited only slightly higher densities in low‐velocity areas (<15 cm/s).

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

“…In addition to creating physical habitats for fishes, wood has a number of biological functions in channels, including increasing nutrient retention (Bilby 1981), creation of surfaces that facilitate primary and secondary production (Benke et al 1985;Coe et al 2009;Lester et al 2009), and providing hiding cover or altering depth and substrate to provide spawning areas for fishes (e.g., Beechie et al 2005;Montgomery et al 1999). Although much early research was focused on wood and salmonid fishes, subsequent studies have documented functions of wood for a variety of non-salmonid fish and invertebrate species (e.g., Angermeier and Karr 1984;Growns et al 2004;Lester et al 2009;Warren et al 2000;Wright and Flecker 2004).…”

“…A major goal of wood placement in streams and rivers is to improve physical habitat such as increasing pool area, habitat complexity, instream cover, and other metrics of fish-habitat quality. These changes are also linked to the amount or intensity of treatment, as there is a strong positive correlation between amount of wood and both physical habitat quality and fish numbers for both natural (Beechie et al 2005;Murphy et al 1984;Naiman et al 2002) and placed wood (Jones et al 2014;Roni and Quinn 2001a). Thus, if the placed wood or wood structures remain on site or function as designed, there typically are significant improvements in habitat.…”

Logjam controls on channel:floodplain interactions in wooded catchments and their role in the formation of multi-channel patterns

“…In turn this influences opportunities for seed dispersal and vegetation colonization and succession . Rare invertebrate and amphibian communities occupy the temporary pools found in floodplain channels and pools resulting in high biodiversity (Nicolet, 1997;Davis et al, 2007), whilst perennial secondary channels are important nursery habitat for juvenile salmonids (Beechie et al, 2005). The resulting dynamic floodplain patchwork is analogous to the Shifting Habitat Mosaic that Table 3 Comparisons between different metrics of channel pattern.…”

Satoyama Landscapes and Their Change in A River Basin context: Lessons for Sustainability

“…Sediment transport and ISSN 2329-521X 2016 www.macrothink.org/iss 54 discharge mechanisms have changed significantly, and ironically, the nutrient that once replenished the river system is now seen as ‗debris' or ‗waste'. Researches indicate that woody debris or organic matters serve vital ecological functions of natural rivers as they help sustain biological diversity and are important for fish ecology during their decomposition and course downstream (Inoue & Nakano, 1998;Wohl, 2005, Dolloff & Warren 2003, Nicol et al 2004Beechie et al 2005). The silt and organic matter supply of the river allowed the rich intertidal zone of the Yatsushiro bay to form.…”