PNNL

Abstract

Stream-dwelling fish face highly-variable environmental conditions from fall to winter due to flux in water temperatures, discharge, and ice conditions. There is a lack of synthesized literature describing the challenging conditions that stream-dwelling fish face during winter. We provide an in-depth description of the interactions between these complex environmental conditions and behaviors of stream-dwelling salmonids during winter for fishery biologists. It is important for fisheries managers to be aware of the conditions that fish confront during winter in order to make appropriate management decisions regarding populations and habitats. We have linked environmental conditions during winter to management needs, described when salmonid movements occur during winter and why, and examined the instream habitats that may be unstable during winter and why. We focused on salmonids in rivers and streams that are in temperate regions where it is cold enough for waters to have ice formations during winter. Diverse habitats, including deep pools with low water velocities, coarse rock substrate, and abundant cover, as well as side channels and backwaters, aid in the survival of overwintering fish. The inflow of relatively-warm groundwater into the water column can be an important factor affecting winter habitat and may either enhance or diminish winter habitat quality for stream-dwelling fish. Considering the length of winter and the vulnerability of fish during winter, a broader understand of winter ice process and their effects on stream dwelling fish can aid in the preservation and improvement of winter habitats.