Effects of experimental flooding on brown trout (Salmo trutta fario L.): The River Sp�l, Swiss National Park

Abstract

Following the construction of two large reservoirs in the late 1960s on the River Spöl, Swiss National Park, flow was greatly reduced and regulated at a relatively constant discharge. The regulated flow regime resulted in the elimination of river changing floods, causing altered and degraded habitat conditions for the brown trout (Salmo trutta fario L.). Although food resources (i.e., zoobenthos abundance) increased after flow regulation, trout spawning areas were greatly reduced by the clogging of coarse sediments. Consequently, the National Park in agreement with power authorities initiated an Aquatic Sciences experimental flood program in 2000 to improve the fisheries potential of the River Spöl. Fish abundance was not reduced by the floods and relatively few fish (< 2 %) were killed or stranded by the floods. In fact, the quality of fish habitat, spawning grounds in particular, was noticeable improved, even though food resources were altered to some degree by the floods. The results showed that the condition of trout in the Spöl remained relatively constant, but the number of redds has increased three-fold since initiation of the flood program.

Movement and Mortality of Adult Brown Trout in the Motupiko River, New Zealand: Effects of Water Temperature, Flow, and Flooding

“…Trout can die because of physical injury caused by substrate movement, or after being stranded in remnant pools on the riverbed or floodplain (Jowett 1997;Ortlepp and Murle 2003). Another potential mechanism of mortality, suggested by our study, may be burial by largescale substrate movement, although we cannot be sure whether the fish located beneath substrate and debris following the flood were dead before burial.…”

“…Trout may also be swept downstream or out to sea. Some studies have indicated that fish displaced downstream by floods have returned upstream during the flood recession (Dedual and Jowett 1999;Dare et al 2002;Ortlepp and Murle 2003). As far as we are aware, there are few direct observations of trout mortality resulting NOTE from floods (but see Ortlepp and Murle 2003).…”

“…However, the effects of floods on adult trout appear to be less severe and unpredictable (Allen 1951;Seegrist and Gard 1972;Jowett and Richardson 1989;Lobon-Cervia 1996). Some studies have indicated that adult and juvenile trout displaced downstream by floods have returned upstream during the flood recession (Dedual and Jowett 1999;Dare et al 2002;Ortlepp and Murle 2003). Therefore, it is not clear whether the reduction in abundance associated with floods observed in some studies is due to displacement or direct flood-induced mortality.…”

“…Therefore, it is not clear whether the reduction in abundance associated with floods observed in some studies is due to displacement or direct flood-induced mortality. As far as we are aware there are few direct observations of trout mortality resulting from floods (Ortlepp and Murle 2003).…”

Climate and land-use changes affecting river sediment and brown trout in alpine countries—a review

“…After hatching, young alevin remain in the gravel until the yolk sac is used up and they emerge as 'fry' from the gravel. In case of severe riverbed clogging before spawning, eggs are either not spawned (Ortlepp and Murle 2003;Mathisen 1955in DeVries 1997 or insufficiently covered by gravel, with an increased risk for wash out with high floods (Everest et al 1987in DeVries 1997. As fines are usually transported downstream by currents during redd construction, the initial percentage of fines in the redd is often reported to be lower (e.g.…”