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Forget Your Scale? Here's How To Closely Estimate The Weight Of A Fish

Do you ever take a scale along when you go fishing just to see what your catch weighs? Did you ever forget your scale and then catch a big fish? No problem! A little algebra can help you out. What! Algebra? Well, that is the price you pay for your forgetfulness. By John Guldin.

Do you ever take a scale along when you go fishing just to see what your catch weighs? Did you ever forget your scale and then catch a big fish? No problem! A little algebra can help you out. What! Algebra? Well, that is the price you pay for your forgetfulness. The following formula will give you an approximate weight for your fish. Actually, it can be fairly accurate, as you will see if you use it. The standard formula is simply:

(G2 x L)/800 = W

I suppose you now regret forgetting your scale! Well, pull out a hand-held calculator, get out a pencil and paper, or in a pinch, take off your shoes and socks.

In this formula "G" is the girth of the fish. This is simply the circumference of the fish at the "thickest" part. Next, "L" is the length. This is the distance from the front part of the fish, assuming it doesn't have a bill, to the fork of the tail (not the tips).

Next, multiply the girth figure by itself. Then multiply that figure by the length, as defined above, and divide by 800. I have tested this formula against certified scales and found it to be a rough estimate of weight, especially with certain species of fish.

Recently, the use of the denominator of 800 has been called into question as being the best number to use. In fact, one author has written an article based upon scientific research and higher mathematics in which he concludes that the denominator should vary depending on the shape of the fish. [Don Peters, "With the Right Mathematical Formula, Take Guesswork Out of Fish's Weight," 2002 World Record Game Fishes, International Game Fish Association, pp. 90-97.] The article carefully describes the various shapes of fish and how different shapes require a different denominator, or "f" factor, ranging from a low of 720 (Wahoo) to a high of 1,228 (Pacific Halibut).

However, Don Peters does state, "If we had just one value to use for "f", 850 would be an improvement over 800," since in the study of 31 species of sport fish the average "f" factor was 848.

While the research and learning goes on in this fascinating subject, and while the formula may prove helpful to those of you who actually enjoy mathematics, I think the lesson to be learned for us mathematically-impaired anglers is, Don't Forget the Scale!

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The "IGFA 2002 World Record Game Fishes" book may be obtained free by becoming a member of the International Game Fish Association, or by ordering the book for $12.95, plus $2.00 for shipping, from the IGFA website: www.igfa.org