Kenai Sockeye Failure Discussion

[Nerka]

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.

[shipbum]

Other questions

I really enjoy these types of posts(especially when the information is substantiated)-but they beg further questions. Other than light level and predation, what else changes copepod numbers? What effect(? food substance) does dead salmon have on Sockey and Silver fry? (we know decaying salmon are a large part of the rainbow diet- I doubt the decaying numbers change the water oxygen content in the Kenai - like they can in the smaller rivers in Kodiak) Are rainbow numbers skyrocketing and increasing predation on fry? I have heard many suspect this is happening -but is there any data to support it-or just talk?

Nerka-is any of this known ,or are these areas of further study?

[shipbum]

Addendum

Note: my above questions are general-not specific to this years poor run but more to understand how many factors influence the average run each year.

[longtimealaskan]

I wondered about the reference to Skilak Lake as the overwintering area. The second run of reds splits into a number of groups that go up a number of different streams to spawn. Reds require a stream with a lake for the fry to overwinter before migrating to marine water. The Russian River has 2 lakes in it's system. I would think the fry would overwinter in the Russian Lakes. Quartz Creek and Crescent Creek dump into Kenai Lake so I would expect fry to overwinter in Kenai Lake. I'm not sure where the spawning area is for the Hidden Lake system. I would expect the fry to overwinter in Hidden Lake but they possibly could overwinter in Skilak. What red streams am I missing? And why would the fry from any of these stream/lake systems overwinter in Skilak?

[Nerka]

good questions

Skilak Lake is the major rearing lake for sockeye salmon. Based on fry numbers and adult production it probably accounts for 70-80% of the average return. Kenai Lake is the next system in line and Russian River is next. Kenai Lake rears fish from those tributaries that dump into it and Russian River (Upper Lake is the rearing area). Skilak Lake appears to rear those fish that spawn at the outlet of the lake (50% of the return based on some observations) and those fish that spawn between Kenai and Skilak Lake - those fry tend to drop down into Skilak Lake.

Relative to sockeye salmon and nutrients these glacial lakes are not nutrient limited. It is light penetration that limits production.

Predation can be an issue but in these glacial lake systems the predator population is very low. Most sockeye rear in the open waters of the lake. Bird predation is low as the glacial nature of the lake provides cover and it is not habitat for rainbows.

If one has a clear water system the whole rearing discussion changes. In clear water systems sockeye tend to stay deep in the lake during the day to avoid bird predation and stay in darker waters. They move up to feed at dusk. In a glacial lake system like Skilak they stay near the surface the whole time - there is two reasons for this - one predation is low and the food resource is there and second it is warmer - temperature impacts growth so staying in warm water makes you bigger.

Hope this helps answer your questions.

[longtimealaskan]

Thanks for the feedback. I didn't know that reds spawned in the mainstem Kenai River or that Skilak Lake played that big a role.

Now another question. Any thoughts about why Skilak Lake is a problem and is causing the red run failure while Tustemena Lake is also very turbid and fed mostly by glacial waters, yet the Kasilof River is having a record run of reds? The two systems are adjacent to each other and the rate pf glacier melt would theoretically be similar. In addition, Tustemena has no large river like the Kenai flowing into it to help flush turbidity out of the lake.

[Nerka]

Kasilof system

You are correct that Kasilof is very turbid. In fact the EZD is about 2 meters and in some years only 1. The spawning area is both the tributary streams and lake spawning. In a study done by the USFWS they estimated that 50% of the spawning took place in the lake.

The average Kasilof return is between 600,000 and 800,000 fish. The average for the Kenai is about 3 million. If you look at the size of Tustumena Lake it is significantly bigger than Skilak. Therefore, while it is more turbid it makes up for it by being larger. Even with the larger size it still does not produce fish like Skilak as the Skilak depth of light pentetration is 4 times greater which is about the level of difference in the average returns.

One concern everyone has with the increased levels of turbidity in Skilak, which started in 2003, is that production may move down toward Kasilof levels.

[longtimealaskan]

The turbidity/light penetration issue for Skilak Lake may be a continuing problem if Skilak Glacier keeps melting at a rapid rate. ADF&G will have to figure out a way to control the amount of turbidity entering the lake or the public will have to accept smaller runs of salmon if nothing can be done. There are possible solutions to the problem that could be explored depending on the amount of money available to throw at the problem.

One of the first things they could look at would be to install silt screens/curtains across the end of the lake where the glacial waters flow into the lake. It wouldn't eliminate turbidity from the glacial waters but it may help reduce turbidity. It probably would not be an inordinately expensive thing to do.

There are also chemical ways to substantially reduce turbidity but they would have to conduct toxicity tests on salmon fry to determine if they could stand low levels of exposure. It may not be feasible to treat sufficient amounts of water for this method to be effective.

[Marcus]

Why?

To my mind — and maybe Nerka can comment — this year's run failure has occurred because the Board of Fisheries, under pressure from interests that want more second run kings in the Kenai, has raised the upper end of escapement goals beyond what are scientifically supportable while restricting the ability of the gill-net industry to intercept the run to the point where too many sockeye are spawning, willfully putting sustained yield at risk. Until the Kenai's second run of sockeye are managed scientifically according to Alaska's constitution, we have no way to rationally pursue sustained yield from that fishery.

While such mismanagement might sit well with the special interests who'd like to see all gill-netting cease in Cook Inlet so that 100% instead of the present 75% of second run kings can enter the river for the sole exploitation of commercial sport/private sport interests, it decimates the area's economy by destabilizing the sockeye yield — up one year, wildly down the next. The area's and state's economies need sustained yield, not wildly erratic yields that are so undependable they furnish no stable economic base upon which to build any sort of industry, e.g., tourism, etc.

BoF and ADF&G must resist politcal pressure to manage Alaska's fisheries any other way than scientifically in pursuit of sustained yield. Putting any one fishery at risk for the sake of special interests in another fishery is deplorable. The loss to area businesses by this year's run failure will have to run in the millions of dollars as restaurants, tackle shops, processors, campgrounds, B&Bs, gas stations, quik-stops and more stand by and watch a steady stream of traffic leaving the area.

[akkona]

Parent year escapements

Here are the escapement numbers for those years that are primarily responsible for producing this year's return as well as a couple of years for which we have already seen the return. These are the final escapement numbers that are a result of subtracting inriver harvest (above the sonar) from the sonar passage estimate:

1998: 551,891
1999: 582,907
2000: 393,276
2001: 457,927

All of these years are at the low end or below the current sustainable escapement goal of 500,000 to 800,000 sockeye salmon. It is difficult for me to see how overescapement played a role in this year's poor return.

[Nerka]

escapement discussion

akkona is correct. This year's return is not directly related to escapements being high. The models ADF&G uses really focus on fry numbers in the lake. In some years escapements in the range cited by akkona can produce lots of fry. In the two rearing years prior to this year return there was 20 million fry in the lake each year. So the issue is how many years in row there are high fry numbers.

If one did a risk analysis there is a higher risk of large fry production and then failure with large escapements than with smaller escapements but you still can get the pattern with smaller escapements - just not as frequent.

A second test is in the system right now. There have been large escapements back to back in recent years. We will have to see how they do. Back in the 80's they did not produce as well as lower escapement years.

[Marcus]

Confused. . .

This year's return is not directly related to escapements being high. The models ADF&G uses really focus on fry numbers in the lake. In some years escapements in the range cited by akkona can produce lots of fry. In the two rearing years prior to this year return there was 20 million fry in the lake each year. So the issue is how many years in row there are high fry numbers.

If one did a risk analysis there is a higher risk of large fry production and then failure with large escapements than with smaller escapements but you still can get the pattern with smaller escapements - just not as frequent.

A second test is in the system right now. There have been large escapements back to back in recent years. We will have to see how they do. Back in the 80's they did not produce as well as lower escapement years.

Well, if I wasn't confused before, I am now. If this year's dismal return is not related to or the result of "overescapement," what is it related to or the result of? Is "overescapement" an issue at all? Is management for sustained yield even possible?

[Nerka]

like to see you confused Marcus

Just kidding. This year's return is in my humble opinion due to a combination of factors all of which combine into one story. First, the number of fry in the lake followed two large escapement - when this happens the number of fry that survive in the second or third year is usually low. Second, those that did survive were only 1g which is on the small side. Small fish means poor survival overwinter - smaller fish have less body fat and that is what they live on overwinter. Smaller fish also means smaller smolt that go out to sea which can also mean lower survival.

Now as to your question. Large escapements in the Kenai can produce large numbers of fry which can start the above pattern. So overescapement is a valid term. However, in some years even relatively small escapements can produce large numbers of fry. It is a game of averages and probabilities.

This is very complex as I mentioned in earlier post so do not feel bad about being confused -

[shipbum]

Why great production of fry/fish

So on the low escapement years that have high production of fry what has happened? Why more fry/spawning fish? Better water temps? Less flooding? More flooding? Mild winters? An unknown variable such as inactivation of egg DNA or proteins when spawning competition/spawning fish crowding is greatest?? Are there far more buffers in the system than we realize? Is fry production always better on years with less escapement? I think my brain just blew a gasket.

[yukon]

Does anyone know what the returns were of the huge spawning year of the oil spill?