Striper kill

[Riverwhy]

I have heard of a possible striper kill down by the dam.  Does anyone have details?

[champ203]

Read about it....but not any details...I am curious too....

[mojorig]

Yes, there is a Striped Bass kill occurring at the Norfork Dam. We knew it was coming. We have been out every weekday since August 21st collecting dissolved oxygen readings and Striped Bass. I have attached a graph showing DO levels at the dam. You can see the deep water refuge for Striped Bass has collapsed. It is called a "Temperature-Oxygen Squeeze." This is fairly common during a high water year on Norfork Lake due to high generation and organic loads. Some reason these kills always occurs on or around Labor Day. These fish kills are mostly Striped Bass with an occasional Hybrid Striped Bass or Walleye (less than 10 of these have been observed).  Similar kills have occurred in 2002, 2004, 2011, and 2015.

This year, the major portion of the kill occurred Sunday Night (9/3) and Monday (9/4). We have picked up 621 Striped Bass (see length frequency below). Of those 621, 141 were collected on Monday (9/4) and 228 on Tuesday (9/5). We are measuring each fish that are not too far gone and have removed otoliths from over 500 fish to be aged. We plan on being out there every day this week and then shifting to every other day for the next week or so.

 

 

[snagged in outlet 3]

Jeremy,

Am I reading the graph correctly?  Don't the fish follow the oxygen up to the 10' to 20' range were it looks to be okay?

What will happen to DO below the dam and the trout there?

Thanks, I find this fascinating.  Pete

[mojorig]

Yes, most fish are found around thermocline (20-30 feet) except for Striped Bass and an occasional Walleye and Hybrid Striped Bass. I have attached a graph that has Temperature and DO. It is very messy.  Once a Striped Bass reaches age-3 (about 20 inches), they can't tolerate the water temperature in August and September at the thermocline. These Striped Bass move toward the dam and occupy the deep bubble of DO that has cooler water temperatures that they can tolerate. Basically, they are choosing comfort instead of food. However, in a high water year, lots of generations cause this bubble to collapse. This results in these Striped Bass kills.

The USACE at the dam will be dealing with the low DO issue until the lake turns over around late October/early November. It is going to be a long fall for them.

 

 

[snagged in outlet 3]

Thanks! 

 

[champ203]

I appreciate all the information shared here.  Much more than I was finding anywhere else.

With 600 plus found so far, and no relief in sight until turnover, is the kill expected to continue but at a slower rate....or will it worsen? 

Is there any way to know the impact to the population from a percentage standpoint?  I assume that would be an educated guess based on surveys....are we talking less than 1% impact, or double digit percentages?

[mojorig]

We suspect that we are on the down hill side of the kill. Yesterday, we only picked up 35 or so fish. Of those fish, less than 5 were fresh (red gills). Every year around the end of September, a high percentage of the Striped Bass leave the dam area and head to pass the state line. We are unsure why but we watch guide reports to see when that shift is occurring.

You are correct about determining the impact of the kill. It would only be a guess. It would unlikely be an educated guess either.  If we were to make a wild guess, it would likely be in the double digits. The reason for that guess is we know we didn't pick up all the dead fish. Some were too far gone. Others got washed into the briars and bushes due to heavy wind and wave action and we just missed them. Finally, not all dead fish float. In fact, studies have shown less than 50% of the fish actually float. So with that being said, we only saw a fraction of the Striped Bass killed.

[Riverwhy]

Jeremy,

 

I really appreciate your work and the update.  Since we are seeing much less mortality amongst the hybrid bass perhaps consideration could be given to significantly increase the stocking rates of this specie. However, I do love catching those stripers!

 

 

[mojorig]

Quick update that we sent out to the Lake Norfork Striper Club (minus the figures):

We wanted to give everyone a quick update about the Striped Bass Kill on Norfork Lake. As of Monday (9/11), we have suspended our efforts to collect Striped Bass and DO/Temp readings. The deep bubble of DO is likely gone by this point (Figure # 1). Paul and Cody only saw one Striped Bass on Monday. It was too far gone to be collected. Combining this information with reports of Striped Bass being caught up the lake, we believe this Striped Bass kill is pretty much over. Thus, we will be suspending our efforts and moving on to sample crappie in Bull Shoals Lake.

We wanted to give a quick recap of what we collected. As you can see in Figure #2, most of the fish collection occurred on Monday 9/4 and Tuesday 9/5. Overall, we measured 663 Striped Bass ranging in size from 19.5 in. to 42.9 in. (Figure #3). We realize this count is not a true reflection of the actual size of the kill. It is likely just a reflection of the amount of fish we could see. Of those 663 fish, we removed otoliths from 469 Striped Bass.

As mentioned in previous emails, we are unable to compare this kill to previous kills due to the difference in the amount of effort during the kill. However, we believe this was a substantial Striped Bass kill.