Hi All,

With respect to the post below and the Perry fish, there
seemed to be some interest for a formula that would accurately
predict the weight of a record class bass.  Until this past
year, there were no formulas that could do this.  The standard
formula used by most anglers (weight = L x G x G divided by
800) tends to over-estimate weight by 15 to 45 percent.  Other
formulas either under-estimate or provide too wide a spread in
their accuracy.

Last year (at the request of In-Fisherman magazine) I
collected data from over 67 certified fish over 14.25 pounds
(most fish were over 16lbs) and developed a formula
specifically for this class of fish.  This was mainly done to
prove the Leaha Trew fish was a hoax.

Anyway, the formula that was developed will accurately predict
the weight of a bass of monster proportions within +/- 5% (for
95% of the fish population).  The formula is:

Weight = Length (Raised to the power of 0.68) x Girth (Raised
to the power of 0.79) divided by 7.0

If you are interested in reading more about the development of
this formula, it was printed in In-Fisherman's Bass Guide 2005
and on BassFanArmy.com.  Rob has a copy of the article for
print too but has not had the time to upload it due to all the
work he's been doing on the site lately.

If you have any question, feel free to ask and I'd be happy to
answer any of them.

Take care

Terry Battisti   

Wow that is complicated :o 

Hey let that Bass go I wanna catch her some day
http://www.calfishing.com/gallery/v/members/tmcustoms/

i was going to ask you "how do you go about finding such
a formula," but will it be covered in the article?

Dude this is a complicated one.
From the Florida fish and wildlife conservation commision. (DFG)

log(weight, in grams) = -4.83 + 1.923 x log(total length, in mm) + 1.157 x log(girth, in mm)

The Florida formula would put Perry's WRB at almost 27 lbs.

Using the formula (L*G*G)/800 Perry's fish calculates to over 33 lbs. This one is generally used for trout/salmon shaped fish and does ok for those.

(G*G*L)/1200 is another widely used formula and is better for bass shaped fish. Perry's bass would calc to 25 lbs. using this one.

The IGFA uses (LxGxG)/914. Perry's record calcs to over 28 lbs.

The formula Terry posted here for the In Fisherman puts Perry's fish at around 21.5 if I remember my math right. Closest so far.

No formula will be exactly accurate. As you can see there can be a fairly large discrepency depending on which one you use.

I also calculated a few other well documented big fish and the results are all over the place.

The results from using differnt formulas for Jed Dickersons Lake Dixon bass go like this.

Weight = 21.69 lbs. L = 28", G = 26.75"

(G*G*L)/1200 = 17.48
(L*G*G)/800 = 25.04
(LxGxG)/914 = 21.92
FLA = 18.82
Terry's formula = 18.47

I hope I did those right :7

MT

Sorry I wasn't able to respiond to this sooner but work got the better of me the last few days.

cst: I developed this formula using a "least square curve fitting method" used in modeling data. Essentially, you gather "good" data and develop a model (or formula as most people cal them) based either on theoretical methods or empiricle methods. This model, because it doesn't incorporate volume in the "powers" is considered "empiricle". much like the formula that mteman provided above that the FL DFG came up with. I cam up with two other theoretical formulas but they weren;t as good as this one. There's a better description of the method in the article that you'll be able to read when it gets posted. Rob is actually going to print the article as submitted. In-Fish deleted a bunch of it because it had too much math in it. LOL.

mteman: Good job dude. LOL. Yep, Dickerson's fish is predicted to weigh 18.47 lbs. I used his fish as one of my data points. What I need are more fish over twenty pounds in order to make it better but getting measurements of 20lb fish is difficult. most of the 20s cauht were never measured.

As for the Fl DFG formula, if you play the game of logrithyms, you can convert it to the following whichy is a bit easier. But you have to remember that it is all in millimeters.

Weight = Length (raised to the 1.923 power) x Girth (raised to the 1.157 power) all divided by 67608.3. This gives the same answer as the log formula and is easier for most to use.

Yes, there is no fool-proof formula that will give exact weight. That's why I always give the deviation when I do stuff like this. Fish like Dickerson's and Long's 20s and other fish may not be as accurate because the data was fit to fish mainly between 16 an 19 pounds. In time, I will be able to develop a better more accurate formula but I'll need the data (fish measurements over 20lbs) in order to do it.

If anyone wants to talk more about this, feel free to email me at battisti@onewest.net.

Take care all

Terry

thanks for the quick reply. i hate statistics but, somehow, that was interesting. :)

TB:

Did anyone ever tell you that you should have been a
scientist?  When I get a another couple of 20's for you I will
get that extra data you need.

XOXO

Dave