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BobT

planimetered vs. littoral?

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I have noticed that when lake acreage is specified, occasionally there are two values mentioned. For example, Lake Osakis is defined as being a little over 6,200 acres planimtered but just over 3,400 acres littoral. Anyone know what these terms mean?

Bob

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Planimetered acres refers to the size of the lake shoreline measured off an air photo. Littoral acres is the area of a lake less than 15 feet deep. This is a very subjective number. It is suppose to represent the portion of a lake where vegetation grows. Well we all know lakes where vegetation grows much deeper, but 15 feet is the number used by the DNR.

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Planimetered acres refers to the size of the lake shoreline measured off an air photo. Littoral acres is the area of a lake less than 15 feet deep. This is a very subjective number. It is suppose to represent the portion of a lake where vegetation grows. Well we all know lakes where vegetation grows much deeper, but 15 feet is the number used by the DNR.


I understood that littoral area was the area of the lake where light could reach the bottom. This would take into account the clarity of the water. I could be wrong but thats what I thought.

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Planimetered acres refers to the size of the lake shoreline measured off an air photo. Littoral acres is the area of a lake less than 15 feet deep.


This is my understanding from all the lake maps that I have ever seen.

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Both are correct. The Littoral Zone is technically the area where plant life can survive in a lake - which is how deep light penetrates. But the way the DNR ESTIMATES the littoral area of a lake is by calculating the surface area of the lake that is 15 feet deep or less. This is a rough estimate, to be sure, but it's better than nothing. You can't base it on transparency because that can vary from day to day; some lakes have a transparency of 20 feet in June and 6 inches in August. They need to have an idea of what the littoral area is because that's what determines how many fish the lake can support. All fish stocking is done on the basis of littoral acres, for example they'll stock 6.5 pounds of fry per littoral acre. Lakes that drop straight down from the shore into 100 feet of water can't support as many fish as a gently-sloping lake of equal size because there isn't enough aquatic vegetation to grow insects and crustaceans.

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well, ya learn something every day. I always wondered about the term littoral...obviously not enough to ask though:)

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well, ya learn something every day. I always wondered about the term littoral...obviously not enough to ask though:)


Yep, guess we can taake these explanations littorally! grin.gif Thanks for the info guys!

Tunrevir~

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This is actually very useful information. For example, if one was previewing a lake where the littoral area was only about 10% of the planimetered, you could draw a couple conclusions. 1. The fish will likely be concentrated into very specific areas and 2. The reproductive potential of the lake may very well be low.

Bob

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