Juvenile salmonid (Oncorhynchus spp.) use of constructed and natural side channels in Pacific Northwest rivers

Abstract

Off-channel habitats, critical components in the life histories of Pacific salmonids (Oncorhynchus spp.), have become increasingly rare in human-modified floodplains. The construction of groundwater-fed side channels is one approach that has been used in the Pacific Northwest to recreate off-channel habitats. We evaluated the effectiveness of this technique by comparing 11 constructed side channels with paired reference sites (naturally occurring channels fed by mixed groundwater and surface water) in western Washington. While total salmonid densities were not significantly different between channel types, coho salmon (Oncorhynchus kisutch) densities were higher in constructed channels and trout densities were higher in reference channels during the winter. Constructed channels were deeper than reference channels and warmer in the winter and cooler in the summer but had lower physical habitat diversity, wood density, and canopy coverage. We did not detect significant differences in water chemistry or invertebrate parameters between channel types. Summer coho density was inversely correlated with minimum daily temperature and with total nitrogen and total phosphorous concentrations. Relative to other stream habitats, both constructed and reference channels supported high densities of juvenile coho salmon during the summer and winter.Résumé : Les habitats hors du chenal, des composantes essentielles du cycle biologique des salmonidés du Pacifique (Oncorhynchus spp.), deviennent de plus en plus rares dans les plaines de débordement modifiées par l'activité humaine. La construction de chenaux latéraux alimentés par la nappe phréatique est l'une des méthodes utilisées dans la région pacifique du nord-ouest pour récréer les habitats hors du chenal. Nous évaluons l'efficacité de cette technique en comparant 11 chenaux latéraux artificiels à des sites appariés (des chenaux d'origine naturelle alimentés par un mé-lange d'eau phréatique et d'eau de surface) dans l'ouest du Washington. Bien que les densités totales de salmonidés ne soient pas significativement différentes dans les deux types de chenaux, les densités de saumons coho (Oncorhynchus kisutch) sont plus élevées dans les chenaux artificiels et les densités de truites plus grandes dans les chenaux témoins en hiver. Les chenaux artificiels sont plus profonds que les chenaux témoins, ils sont plus chauds en hiver et plus frais en été, mais ils possèdent une diversité d'habitat physique, une densité de bois et une couverture d'arbres plus faibles.

The floodplain food web mosaic: a study of its importance to salmon and steelhead with implications for their recovery

“…However, this assumption has never been adequately tested in salmon bearing streams. Although a few studies have calculated the density or standing crop biomass of the food base in these side channels (e.g., Morley et al 2005), this is the first study to undertake the additional efforts necessary to calculate annual food base productivity (i.e., secondary invertebrate production and terrestrial invertebrate fluxes), which are a necessary component of ecosystem-based energetic approaches (Odum and Barrett 2005). In fact, utilizing biomass or standing crop estimates in energetic analyses can produce paradoxical results (i.e., Allen's paradox; Hynes 1970, Waters 1988, whereby the amount of production at one trophic level is insufficient to support observed consumption at higher trophic levels (Allen 1951).…”

Differences in river ecological functions due to rapid channel alteration processes in two California rivers using the functional flows model, part 2—model applications

“…Consequently, pool tail/riffle entrance is one preferred location for spawning (Montgomery et al, 1999;CoulombePontbriand and LaPointe, 2004;Moir et al, 2004;Moyle and Check, 2004). Other locations include side channels and lateral bars (Webb et al, 2001;Moir et al, 2004;Morley et al, 2005).…”

Lower Scotts Creek Floodplain and Habitat Enhancement Project

“…Coho Salmon disperse to instream structures and off-channel habitat features in summer and winter to seek temperature and velocity refuge (Morley et al 2005;Whitmore 2014). Constructed offchannel habitat was utilized at a rate comparable to or higher than natural off-channel habitat features (Morley et al 2005).…”

“…Constructed offchannel habitat was utilized at a rate comparable to or higher than natural off-channel habitat features (Morley et al 2005). Off-channel pond temperatures were presumably attenuated by groundwater inputs which provided temperature refuge in summer.…”

“…Off-channel pond temperatures were presumably attenuated by groundwater inputs which provided temperature refuge in summer. Constructed off-channel ponds had higher temperatures in winter and lower temperatures in summer compared to natural features (Morley et al 2005). Restoration of instream and off-channel habitat through the construction of large wood structures and off-channel ponds increased overwinter/oversummer survival, and growth/retention rates (Gallagher 2012;Whitmore 2014).…”