F
FromTheHills
0
Although we had some pretty wet weather around Christmas and New Year's, it's been pretty dry since then. On the USGS gauge, the Siletz is currently in between the 10th and 20th percentile of flows-- meaning that only 10-20 percent of a discharges for the past 30 years of flow data, for this time of year, has been equal to or below this number. In other words, Oregon's rivers are running low, pretty darn low for more than a month. Low flows are seen throughout the Willamette basin and coastal streams.
So, are the winter steelhead runs matching the predictions?
ODFW's 2009 Winter Steelhead Forecast
I recently quizzed some biologists about the effects of low flows on the winter runs. In the Yaquina system, for example, the word is that the fish are still stacking low because of decreased seasonal flows.
Here' some info I pulled up from research from UC Davis, just out of interest:
"Adult steelhead movements are most rapid and uniform when the hydrograph is either falling or rising. However, as a declining hydrograph drops to certain low levels, there are distinct thresholds at which adult movements begin to slow and then eventually stop altogether. As these thresholds are crossed, more and more fish end up “stacking” in certain “favored” pools and runs."
"...spatial distribution of spawning can and does vary widely between years and even within the same year. The controlling mechanism appears to be flow, with adult steelhead very definitely “going with the flow.” For example, in overall high-flow years (e.g., 2006), spawning is focused in uppermost stream reaches that fish are able to access, including areas only rarely utilized. In overall low-flow years, much more spawning occurs in higher-order downstream reaches, including the main stem of the river. However, within any given season, a shift to more spawning downstream can and does occur when the river hydrograph is in rapid decline, or the end of the spawning season (i.e., roughly mid-April to mid-May) is nearing."
"During the majority of the spawning season, from roughly December through March, a single stacking and holding event, due to low flows, may last weeks or even months. Invariably, a freshet will occur, however, sending fish on their way up- and down-stream. However, in April and May at the end of the spawning and rainfall seasons, there is a “tipping point” during prolonged low-flow periods, beyond which adults leave places where they are stacked and begin moving out of the river system; this occurs despite the difficulties (i.e., physical barriers) and risks (due to increased predation). The tipping point phenomenon likely occurs in response to increasing day length and water temperatures, and is why very few adult steelhead become trapped in the river over summertime in most years."
So, do a rain dance and they will come??
So, are the winter steelhead runs matching the predictions?
ODFW's 2009 Winter Steelhead Forecast
I recently quizzed some biologists about the effects of low flows on the winter runs. In the Yaquina system, for example, the word is that the fish are still stacking low because of decreased seasonal flows.
Here' some info I pulled up from research from UC Davis, just out of interest:
"Adult steelhead movements are most rapid and uniform when the hydrograph is either falling or rising. However, as a declining hydrograph drops to certain low levels, there are distinct thresholds at which adult movements begin to slow and then eventually stop altogether. As these thresholds are crossed, more and more fish end up “stacking” in certain “favored” pools and runs."
"...spatial distribution of spawning can and does vary widely between years and even within the same year. The controlling mechanism appears to be flow, with adult steelhead very definitely “going with the flow.” For example, in overall high-flow years (e.g., 2006), spawning is focused in uppermost stream reaches that fish are able to access, including areas only rarely utilized. In overall low-flow years, much more spawning occurs in higher-order downstream reaches, including the main stem of the river. However, within any given season, a shift to more spawning downstream can and does occur when the river hydrograph is in rapid decline, or the end of the spawning season (i.e., roughly mid-April to mid-May) is nearing."
"During the majority of the spawning season, from roughly December through March, a single stacking and holding event, due to low flows, may last weeks or even months. Invariably, a freshet will occur, however, sending fish on their way up- and down-stream. However, in April and May at the end of the spawning and rainfall seasons, there is a “tipping point” during prolonged low-flow periods, beyond which adults leave places where they are stacked and begin moving out of the river system; this occurs despite the difficulties (i.e., physical barriers) and risks (due to increased predation). The tipping point phenomenon likely occurs in response to increasing day length and water temperatures, and is why very few adult steelhead become trapped in the river over summertime in most years."
So, do a rain dance and they will come??
