Topwater Caranx Ignobilis: Giant Trevally (GT) > Tackle & Techniques

Weighing fish

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Kamalu Charlot:
A few I have seen to take weights- Local whipper KPC's formula= Fork Length X Fork Length X Girth X 2.75 divided by 10,000. Another one- Girth x Girth then multiply by Length and divide by 800 = total weight.  There is another one I forgot also A very interesting paper on the GT with lots of formulas and info for the die hards.  Any more papers like it feel free to post (Life History and Ecology of Large
Jacks in Undisturbed, Shallow,
Oceanic Communities) http://swfsc.noaa.gov/publications/CR/1991/9173.PDF

Mark Harris:
Hi Kamalu

First, thanks so much for that paper extract. I have printed it and am avidly trying to absorb some of the findings already. Absolute gold for those anglers who really want to understand and respect their quarry.

The ((girth x girth x length) / 800) formula does not work as far as I can tell. For example, a hypothetical fish of fork length 120 and girth 100 which you might expect to be in the high 30s, comes out at 15 kilos!

I think Fl x Fl x girth x 2.75 is the Nomad formula?

Will Wragg:
Bula all,

I am in agreement with Simon and Doug.

I mostly fish alone and if I want to weigh a fish I slide it into a Kevin Nash Carp sling, which can take fish up to 45 kg, and then lift the fish out and weigh it on 100kg Salter dial scales. I don't usually photograph fish, so it goes back the same way.

I must admit I haven't done this with Gts over 30kg, but with two anglers it should work fine. I have weighed a 50kg Giant Clam like this too!

When I used to work on Lake Nasser, we welded a ring on to the canopy of the boat and had the scales semi permanently mounted, so the sling and fish could go straight on. This was great for big Nile Perch. The issue back then was finding a sling big enough, although there are several now available.

On the subject of fish care, English anglers lead the way with unhooking mats, antiseptics etc. Some of this is a little excessive, but I have soft rubber matting in the bottom of my boats, which is nice to stand on and goes a long way in preventing damage if fish thrash around.

Jay Burgess:

--- Quote from: Mark Harris on March 29, 2012, 12:19:56 PM ---
The ((girth x girth x length) / 800) formula does not work as far as I can tell. For example, a hypothetical fish of fork length 120 and girth 100 which you might expect to be in the high 30s, comes out at 15 kilos!


--- End quote ---

Why do I get 1500kg?? how are you putting in the lengths Mark?

Mark Harris:
Same thing Jay absent a base dividing factor.  If you are putting in the measurements as cm, then you need to divide the answer by 100.

This is also the case with the much quoted Nomad formula - you actually need to divide by 100,000 and not 10,000 as is usually stated.

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