Pacific Southwest

Title: Effects of stream channel morphology on golden trout spawning habitat and recruitment.

Author: Knapp, R.A., V.T. Vredenburg, and K.R. Matthews.

Date: 1998

Source: Ecological Applications 1104-1117.

Description: Abstract. Populations of stream-dwelling salmonids (e.g., salmon and trout) are generally believed to be regulated by strong density-dependent mortality acting on the age-0 life stage, which produces a dome-shaped stock-recruitment curve. Although this paradigm is based largely on data from anadromous species, it has been widely applied to streamresident salmonids despite the fact that the processes limiting or regulating stream-resident populations remain poorly understood. The purpose of the present study was to determine whether stream channel morphology affects the availability of spawning habitat for California golden trout, and whether spawning habitat availability influences the production of age-0 trout and recruitment into the adult population. Wide stream reaches contained significantly more spawning habitat and a higher density of nests and age-0 trout than did narrow reaches. In contrast to the idea that salmonid populations are regulated by density-dependent mortality of age-0 fish, we found that the mortality of age-0 trout was largely density independent. In addition, over most of the range of observed fish densities, the density of a particular cohort was positively correlated between years for age-0, age-1, and age-2 trout. Therefore, our golden trout study population was limited by spawning habitat, with spawning habitat availability influencing the production of age-0 trout as well as recruitment into the adult population. Grazing by cattle has widened the study streams, and our current findings help to explain why stream sections subject to grazing had more spawning habitat and higher golden trout densities than ungrazed sections. Individual growth rates of golden trout are apparently negatively density dependent, and these grazing-related increases in trout density have likely resulted in decreased growth rates. Our study demonstrates that it is only by gaining an understanding of how processes operate that we will be able to predict the effects of habitat alteration on populations.

Keywords: golden trout; livestock grazing; recruitment; reproduction; salmonids; Sierra Nevada; spawning habitat; stream alteration; stream morphology

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Citation

Knapp, R.A., V.T. Vredenburg, and K.R. Matthews.  1998.  Effects of stream channel morphology on golden trout spawning habitat and recruitment..   Ecological Applications 1104-1117..