Habitat Utilization by Juvenile Pacific Salmon (Onchorynchus) in the Glacial Taku River, Southeast Alaska

Abstract

Habitat utilization was determined in summer 1986 by sampling 54 sites of nine habitat types: main channels, backwaters, braids, channel edges, and sloughs in the river; and beaver ponds, terrace tributaries, tributary mouths, and upland sloughs on the valley floor. Physical characteristics were measured at all sites, and all habitats except main channels (current too swift for rearing salmon) were seined to determine fish density. Sockeye (Oncorhynchus nerka) averaged 23 fish/100 m2, nearly twice the density of coho (O. kisutch) and four times that of chinook (O. tshawytscha), 14 and 6 fish/100 m2, respectively. Sockeye were age 0, 27–84 mm fork length (FL), and most abundant in upland sloughs, beaver ponds, and tributary mouths. Coho were ages 0 and 1, 33–132 mm FL, and most abundant in beaver ponds and upland sloughs. Chinook were age 0, 40–93 mm FL, and more abundant than the other species in habitats with faster currents (1–20 cm/s), particularly channel edges. Each species was absent from about one-quarter of the seining sites of each habitat type. Thus, the lower Taku River provides important summer habitat for juvenile salmon, but many suitable areas were unoccupied, possibly because of their distance from spawning areas and poor access for colonizing fish.

Ecology of Juvenile Salmonids in Shallow Tidal Freshwater Habitats in the Vicinity of the Sandy River Delta, Lower Columbia River, 2007

“…Juvenile fall Chinook salmon generally prefer faster water and smaller substrates, and are less associated than other salmonids with cover and backwater habitats such as ponds and sloughs (Chapman and Bjornn 1969;Taylor 1988;Murphy et al 1989). Bottom et al (1984, cited in Fresh et al 2005 found that yearling Chinook salmon in intertidal habitats of the Columbia River spent less time in shallow habitats and more time in deeper channel habitats than did subyearlings.…”

Hood River Production Program Review, Final Report 1991-2001.

“…We assume that a majority of the invertebrate production will come from the portion of the riffle that is shallower because there is less current and more sunlight penetration. This assumption can be supported by the observation that significant rearing of juvenile salmonids occurs in margins of highly turbid rivers in Alaska (Murphy et al 1989). Since the equation was developed for small streams, we assumed that effects in larger streams was equivalent to effects realized at 0.5m in depth (the deepest value for which the equation calculates).…”

“…Further, Ptolemy's model incorporating the suspended solids function was not validated with data outside British Columbia, and is based on data for all salmonid species and all life stages. Evidence exists suggesting that not all species or life stages react to TSS in the same manner (Sigler et al 1984;Murphy et al 1989;Servizi and Martens 1987).…”

“…This confounds many between basin and between study comparisons of NTU because similar NTU's may correspond to different TSS concentrations. Murphy et al 1989 showed that different species react differently to TSS. They found in the glacially turbid Taku River, Alaska, that both sockeye and coho had significantly lower densities in highly turbid water (JTU>400) than in less turbid water.…”

Low potential for restraint of anadromous salmonid reproduction by beaver Castor fiber in the Numedalslågen River catchment, Norway

“…Dams built by North American beaver C. canadensis have in some instances been shown to temporarily limit the upstream migration of adult anadromous salmonids and the downstream movement of juveniles, particularly during periods of low water flow (Murphy et al, 1989;Gibson et al, 1996;Alexander, 1998;Cunjak and Therrien, 1998). Beaver dams may also be detrimental to anadromous salmonid spawning by reducing stream flow and by causing siltation of spawning gravel (Knudsen, 1962;Swanston, 1991;Halley and Lamberg, 2001).…”