Estimating a Muskie's Weight
Posted: Mon Jun 25, 2007 6:50 pm
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.
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.