Length -v- Girth for determining weight of fish...

[JohnR]

Have any of you used the Legth-v-Girth method of determining a fish's weight?
I tried it on a couple sample measurements I knew ( including #^&#^&#^&#^&#^&#^&'s 50) and the few times I tried it and it looked about right...

The formula is Girth x Girth x Length / 800 =Weight


His fish had a girth of 29.5 inches and a length of 48 so 29.5 x 29.5 x 48 / 800 = 52.215 and the fish hit the scales at 52.5 pounds when weighed on a certified scale...

Just figured that this would be the way that the catch and release fish for the year long would work out (will still accept weigh in slips for kept fish (East Tide :P ), will have a list of "approved" B&Ts for when this kicks off on May 1st)...

[DamonM]

While fishing this fall with Jeff H, we got into a slug of big fish in the 30 pound class. We both had 30 pound boga grips which were bottomed out by every fish. Our solution was to double up the bogas and combine the readings on the two scales. I was skeptical about the accuracy of this method until I weighed a fish which registered a dual reading of 22 and 18 pounds. I released the fish after measuring the length and girth. The fish was 45.5 inches long with a girth of 26.5 inches. The formula comes out to 39.94 pounds. I'd say thats good enough for government work.

[Blitzseeker]

I know a guy has caught tons of 25 lb plus fish over the last several years. He always uses this method on the beach to estimate what the weight will be. He's told me that he's never been off more than about 2-3 pounds, and that is in the spring when I guess this method systematically overestimates weight by about a pound or two(for 25 lb plus fish). After mid-summer he claims it's right on.

I like it, because I don't like killing fish except for a couple good meals a year. It's close enough for me.

[nor-easter]

Hey Damon
When you doubled up those Bogas, did you put them end to end or side by side?
Thanks for the info!

[JohnR]

Would it need to be end to end daisy-chained for accuracy or would both work??

[Got Stripers]

I've got a berkley 50# digital scale and I can weigh a fish and release it a lot quicker than getting a length and girth measurement. I question how that is a quicker method and I certainly don't think it's better for the fish. You would need to lay the fish down on the sand to get the measurements, which removes slim coat and might lead to infection death down the road.

When I'm out my scale is easy to get at and a fish can be weighed & released in about 30-60 seconds, like to see someone get those required measurements in the same amount of time. Personally, I don't care and only weigh the fish when I think they are over 30 lbs.

Tight lines.

[Saltheart]

end to end won't work. both will be over range since both must hold the entire load. got to be side by side to share the weight and get both in range.

[JeffH]

Saltheart has it. It's Physics 101.......

[Slipknot]

Now I remember why I dropped out of Northeastern- mechanical engineering. That darn physics was killer.

[Patrick]

GS,

I agree with the film removal thing. The less time out of the water the better. The only thing about a scale, you gotta watch out for gill damage.

It doesn't even matter how big the fish are anymore to me anyways. I just like to get out, throw some bait or some lures, joke with the buddies, be thankful I'm alive. I usually try a conservative estimate of the size of the fish for bragging purposes but other than that, not a care.

There is another method to all of this madness. See if you can get someone to snap a photo. Then. using the photo, look at something in the shot the same distance from the camera, such as your hand. Measure your hand in real life, measure your same hand in the picture. Using that, you can find out the scale of the photo. Then you can find out the length of the fish and closely estimate the girth. Simply use the formula stated above.

This method was used to determine that an IGFA record small mouth was a fraud. As it turns out, the angler caught a bragging right sized small mouth out of the Dale Hollow Resovoir(I think) but to make it a world record, he stuffed lead weights and other heavy objects down the smallmouth's mouth. The scientists that review the claims of world record fish used the method I described in conjunction with the equation posted above. If the fish was actually the weight given, the man would have had 8 inch wide palms. The average man's palm is about 3.75 to 4 inches.
I actually learned this stuff in school. Geometry and when I worked in the school's print shop. It pays to pay attention.
You know what they say about wide palms don't you? ;D

Oh yes, I forgot to give an example of what I mean.

Allright suppose in the picture my hand was .5 inches wide. in real life say my hands are 4 inches wide.

Take .5 and put it over 4 so it's .5/4. Now say the fish was 15 inches in the photo.

so it's .5/4 = 7/X Then cross multiply. .5X=28. Divide .5 from each side. X=56 I think. So the fish would be 56 inches. Of course these are all made up numbers. I have no clue how big my hands are or how big they would be in a photo. It's just an example for people who forgot or didn't learn how to do proportions.

[JohnR]

Patrick, I don't know about your formula but as far as weighing the fish at the gill, that might work on a little fish but you shouldn't do it there ona big fish. I use the same 50# digital Berkely scale as GS and it works great. I catch the fish at the bottom jaw. Fairly quick and painless.

Quick measuring with a tape can be done fairly quickly to if you are ready for it and do it right at the beach. If you need to run 50 yards to grab your tape you might as well just turn the fish around without measuring...

[Jenn]

Patrick...I just heard a loud POP when I read your post......I think you have just finished me off....I am now completely insane because of your post!!! Now you can explain to my doctor why she needs to increase my prescription.....

Honestly....why would ANYONE go through so much trouble to find these things out???? What ever hapeened to the almighty fish tale?????Heehee

I dunno.....I just want to "be fishing".....wind, salt, sun, fog, sand..........ahhhh!!! I am relaxing just thinking about it! Hmmmmmm.......!!!!! see now isnt that better???

[JohnR]

Patrick, your method would require a waterproof, left-handed slide rule. Stick to the Girth x Girth x Length / 800 =Weight method or pick up the digital scale... And tell whoever is dropping sugar cubes into yuor latte to knock it off (that was what is known as a joke, not a tweak or meaness :P )

[Saltheart]

A waterproof , lefthanded slide rule!! I like it. Believe it or not , I actually used a slide rule my first 2 years at WPI. Then we all got TI SR50 calculators. That sure made life easy....but I digress.

[JohnR]

The "250" in TI 250 was probably the price for it too. I manage computer systems for roughly 250 CAD and engineering types (well 175 or so actually do engineering or CAD) and there is a small percentage, even some of the younger ones, that turn out work with some influence of the slide rule... Not EVERYONE requires a computer :P