I thought I would start a new thread since the overescapement thread is getting so long.
I wanted to clear up some data issues on why the Kenai River sockeye salmon return is poor this year. In the Daily News Craig Medred put the blame on turbidity in Skilak Lake. That is not the cause and Craig has not checked out the data. I even fell into the trap as turbidity has been reduced in the lake in recent years so decided to get the data from ADF&G.
So here are some facts that should help the discussion:
1. The depth of light penetration in Skilak Lake in the rearing year for this year's return was 8.7 meters - this is very good and on the high side - turbidity from glacial melt was not a factor. Glacial melt did not impact the lake until the next year when the depth of light penetration was only 4 meters.
2. The size of the fry was 1.0 grams which is smaller than optimum but survival is still good at this size. Smaller fry at 0.5 grams has been measured only recently.
3. It is not marine survival - Kasilof, Kenai, and Susitna River stocks are coming in on forecast which uses past marine survival data in the model.
The Kenai return was forecasted at this level based on fry numbers and size of the fry.
4. The number of fall fry in the lake appears to be a direct result of the brood year interaction between the previous year's fry (greater than 20 million) and the fry from this year when they entered the lake. The fall fry estimate was on 8.7 million for this year's return.
So in conclusion, turbidity, small fry size, or marine survival does not appear to be the root cause of this year's poor return. Instead it appears to be a direct result from competition between last years return and this year's return when they were in the lake together in the spring of 2002. Food resources were down since the 20 million fry had cropped it down in the summer of 2001 and these low levels in the spring of 2002 had to feed both brood years - the new year class did not survive this competition very well.
I hope this helps to keep the data in the discussion. For the record, this seson is not over and Kenai still could come in better than forecasted. The clock is running out but until the season is really over we will not know. In some late years a large fraction of the Kenai return can come in August. However, at this point there is nothing in the data that says Kenai is strong or even average.
I wanted to clear up some data issues on why the Kenai River sockeye salmon return is poor this year. In the Daily News Craig Medred put the blame on turbidity in Skilak Lake. That is not the cause and Craig has not checked out the data. I even fell into the trap as turbidity has been reduced in the lake in recent years so decided to get the data from ADF&G.
So here are some facts that should help the discussion:
1. The depth of light penetration in Skilak Lake in the rearing year for this year's return was 8.7 meters - this is very good and on the high side - turbidity from glacial melt was not a factor. Glacial melt did not impact the lake until the next year when the depth of light penetration was only 4 meters.
2. The size of the fry was 1.0 grams which is smaller than optimum but survival is still good at this size. Smaller fry at 0.5 grams has been measured only recently.
3. It is not marine survival - Kasilof, Kenai, and Susitna River stocks are coming in on forecast which uses past marine survival data in the model.
The Kenai return was forecasted at this level based on fry numbers and size of the fry.
4. The number of fall fry in the lake appears to be a direct result of the brood year interaction between the previous year's fry (greater than 20 million) and the fry from this year when they entered the lake. The fall fry estimate was on 8.7 million for this year's return.
So in conclusion, turbidity, small fry size, or marine survival does not appear to be the root cause of this year's poor return. Instead it appears to be a direct result from competition between last years return and this year's return when they were in the lake together in the spring of 2002. Food resources were down since the 20 million fry had cropped it down in the summer of 2001 and these low levels in the spring of 2002 had to feed both brood years - the new year class did not survive this competition very well.
I hope this helps to keep the data in the discussion. For the record, this seson is not over and Kenai still could come in better than forecasted. The clock is running out but until the season is really over we will not know. In some late years a large fraction of the Kenai return can come in August. However, at this point there is nothing in the data that says Kenai is strong or even average.
Comment