Estimating a Muskie's Weight

[Don Wittenberger]

The tradition of judging fish by their weight is deeply ingrained in our fishing culture, so naturally many anglers want to know what their "big fish" weighs. Unless you are certifying a fish for a new state record, you don't need a verified weight, and there are several methods of estimating a tiger muskie's weight that are reasonably accurate for all other purposes.

1. The "Quick and Dirty" Method

An experienced angler can tell by looking at fish about how much they weigh. The way you do this is measure its length, use a benchmark weight, and subtract a little for a "skinny" fish or add a bit for a "fat" fish. Typical weights of tiger muskies are: 36 inches = 12 lbs., 40 inches = 16 lbs.; to break 20 lbs., you usually need a 43-inch fish, and 45 inches to break 25 lbs., and 48 inches to 50 inches to break 30 lbs.

2. Tackle Box Scale

Most fishing scales are spring-operated, and springs tend to stretch over time, so the older the scale is, the less accurate it is. Also, the error tends to increase with the weight of the fish. You can determine your scale's error by weighing 1-gal. plastic milk jugs filled with water. A gallon of water weighs 8 1/3 lbs. (or 8.3452641 lbs. if you like to be exact), so 3 jugs weighs 25 lbs. Using this method, I discovered my scale weighs about 1 lb. too high above 30 lbs., so if my scale shows 30 lbs., I know the fish weighs about 29 lbs.

3. Mathematical Formula

The universally accepted formula for calculating a muskie's weight is L X G X G / 800, where L = length and G = girth. There is some evidence this formula actually understates fishes' weight a bit, as Wisconsin guide John Detloff compiled statistics on thousands of muskies caught from the Chippewa Flowage and came up with L X G X G / 754, based on actual weights of the fish. His data are reliable, because there has been intensive record-keeping on the Flowage for decades, and Detloff has a certified scale at his resort and there's another one at Hermann's Landing. It should be pointed out that Detloff's number isn't necessarily precisely accurate for Washington State's tiger muskies, because he's measuring true muskellunge that live on a different forage base. What time of year the majority of fish are caught can also skew this statistic, as fish tend to be heavier in late fall, and Wisconsin anglers can fish later into the season than we do because they're allowed to use live fish for bait.

To illustrate how the formula works, let's use the fish that Kenster caught at Lake Tapps yesterday as an example. K said his fish was 43 inches and weighed 21 lbs., 3 oz. (21.2 lbs.). He didn't tell us its girth, but the 42-incher I caught at Mayfield last week had an 18 inch girth, and was slightly on the skinny side, so let's assume K's fish had a girth of 19 to 20 inches. If we calculate his fish's weight by both formulas, we'll get weights bracketing the reported weight of 21.2 lbs., i.e.:

43 X 19.5 X 19.5 / 800 = 20.4 lbs.
43 X 19.5 X 19.5 / 754 = 21.6 lbs.

So, 21.2 lbs. looks like a pretty good number.

The only tools you need to "weigh" fish this way is a 60-inch cloth tape measure of the type used by seamstresses (and available at fabric stores), and a small pocket calculator with a square root function. Measuring the fish's length and girth, and computing its weight on a calculator, takes only a minute or two. Then, you can record its length and weight in your fishing log, or your Angler Diary -- hopefully, you are participating in WDFW's Volunteer Angler Diary Program.

I consider this method more accurate than either of the other two; in fact, I double-check the weights I get from my tackle box scale by doing the formula calculation. If someone tells me he used the formula method to determine his fish's weight, I'll accept it as a valid weight for bragging purposes.

Note, if your estimate indicates you've got a state record fish (currently 31.25 lbs.), you'd better not waste any time getting it to a certified scale, because fish begin losing weight as soon as they're killed and removed from the water. Waiting 24 hours to get the fish weighed could cost you several pounds. One of your best bets for finding a certified scale big enough for a 31-lb.-plus fish is the nearest post office. Make sure you get witnesses who observe the weighing to sign an affidavit. Then take it to a regional office of WDFW for inspection by a biologist before having it frozen for the taxidermist. Freezing a fish before it's examined by a state biologist will disqualify it for the state record.

[Kenster]

Don great info....I am going to go get a cloth tape so I can start measuring the girth of these bad boys, and compare the digital scale to the measurements. Does this work the same for Bass large and small? On a side note I have compared my scale to others in the past and have been within an ounce on a 5 pound bass, I just couldn't believe the 1in difference on the other lake Tapps post (27pounder) could make a 5.75pound difference. and the Muskie I caught had a rather deformed tail. However, using the mathmatical calculation

(44)(x)(x)/800=27 gave that fish a 22.15inch girth Fat fish!

Thanks again!!
Kenster

I should alway proof-read my comments.

[Don Wittenberger]

The formula is different for bass, because they have a different body build. A formula that supposedly works for both largemouth and smallmouth is L X L X L / 1600. The web site I found that on, also has a conversion chart based on fish length. http://www.windycityfishing.com/bass_co ... _chart.htm

[CraigVM62]

I have a couple of spring based scales that I test now and then via barbell weights to confirm they are still pretty accurate. These all have a typical large hook which I normaly just hook under a salmons gills to hoist and weigh. The problem with the TM's is I don't want to do any thing that can damage them before releasing. Would one of those "Lip Grip" type scales be the best ? I think I saw someone say that picking up a large TM by the jaw can cause damage to them.
I have thought that perhaps the ideal method would be to land them via one of those square landing nets such as Dave R uses. Then weigh the fishin in the net, and subtract the known weight of the net.

[Bill G]

Weighing the fish in the net and subtracting the net weight is the best idea. You don't have the fish out of the water for very long you dont get bit and don't slim your boat. The cradle is great for measuring the fish but sucks for weighing. I think I will use Don's caculator to guestamate weight.
Bill

[Deadeyemark]

Most folks in the musky fishin arena go by length, period. Girth is included if you want or it it's a good fish. Most people wouldn't know how much they're fish weighed simply because length has been the standard for years.
Hanging a musky or a good bass/walleye also by the lip is NOT good for the fish.
I do my length measurements in the water with a sewing tape, then just let the fish swim off.
Remember, the less handling the better.