January 22, 2020 - Technical Report on Striped Bass Physical Condition

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wayne gustaveson

Staff member
We had a successful fishing trip on Wednesday with some afternoon sunshine and cooperative stripers. We trolled to find striper schools and dropped spoons to the bottom to catch fish. We found 4 different schools at depths ranging from 40-70 feet. It was hard to hold the school in place as they drifted off within 10 minutes after discovery. We had 3 anglers in the boat and dropped spoons immediately when fish were seen on the graph. At the end of the day we had 30 fat stripers in the cooler and headed back to Wahweap. The numbers caught were average for winter fishing but the physical condition of Lake Powell stripers continues to amaze me. Here is an analysis of how stripers compare in physical condition between years at Lake Powell.

Quagga mussels were discovered in 2012. The last real healthy striper population occurred in 2014. Since then stripers have been slim and lean. We can measure physical condition with the K Factor which is a ratio between length and weight that is comparable among striper year classes year after year. The equation
proposed by Fulton in 1904, assumes that the standard weight of a fish is proportional to the cube of its length:

{\displaystyle K=100(W/L^{3})\!\,}

Basically, the average condition of a fish equals 1.0. Fat fish are on the positive side of 1 (1.2 to 1.4) while skinny fish are on the negative side (0.75 to 0.95) Juvenile fish tend to have a higher K factor than adults because they can eat plankton as well as shad and they can feed in warm water during the summer. .

Here is the history of Lake Powell striper Condition since 2014:

Striped Bass are in better condition now than they were before quagga mussels completely dominated Lake Powell. The reason for this is that shad numbers peaked in 2019 and have continued to be strong through the winter of 2019-20. If stripers have enough forage to eat they will be fat and healthy.

In 2014 the K factors for Juvenile and Adult stripers was 1.41 and 1.23.
K factor declined slightly in 2015 to 1.24 and 1.09
2016 showed a large drop down to 1.31.and 0.80
2017 stayed low at 1.29 and 0.90
2018 saw a big increase in juvenile to 1.41 but adults remained at 0.88
Then in 2019 the good times returned with 1.33 for juvenile and 1.19 for adults.
It continues through the winter with 1.42 and 1.20

The 1.42 K Factor is amazing as the juvenile fish caught were almost adults (16-18 inches) compared to the juveniles that were 12-15 inches in the lean years.

That is enough science for today. Here is something easier to understand:

Adult stripers and smallmouth bass are Fat

Smallmouth are Fat


And we had some sun in the afternoon.


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