Estimating GT Weights

[Kasey Leong]

Possibly a bold statement to make, but I reckon with experience you can call a GT's weight just by looking at the shape of its head. Actually, a friend of mine first gave me this idea and after a while, it gradually caught on to me. Of course, this guy has seen ALOT of GTs.

Obviously, this would be an approximation and I would say you have to allow for a reasonable margin of error (maybe +/- some 5-10kg) but I reckon its possible. Allow for a slightly greater margin of error (+/- some 15kg) when using a wide angle lens.

At worst, this will be a good game!

What do you guys think?

[jonathan_tan]

A friend of mine shared a formula with me for estimation.

girth x girth x fork length (cm) x 2.70 divided by 100000

Assuming a girth of 90cm and fork length of 110cm

(90 x 90 x 110 x 2.7 ) / 100000 = 24kg

I haven't had an opportunity to measure and weight a sizaable fish. I will make an effort to do so for my next trip. If one of the forummers has the opportunity to apply and share the results, i think it would make some interesting discussons. 

[Graham Scott]

I use size of mouth to estimate weight;
swallow a tennis ball...8kg
swallow a grapefruit.....18kg
swallow a football.........35kg
swallow a footballer....HUUUGE

[jonathan_tan]

hahahah.... size of the ball matters! 

[Angus Hulme]

I reckon with experience you can call a GT's weight just by looking at the shape of its head.

Hi Kasey, what are the visual cues in relation to it's head shape?

I always thought examining the size of the fishes eye in relation to it's body size gives a clue, ie, the smaller it's eye, the bigger the fish.

Certainly couldn't use that alone to estimate the size of fish, I know, but using your method, I'd be interested to know what size you would think this fish is supposed to be in my pencil illustration below.......?

[Kasey Leong]

Hi angus,

Wow, thats a nice sketch! A little bit harder, but I'm going to guess between 5-15kg. Say 8kg.

Estimating the weight by formula is one thing, but I'm referrring to estimations just based on a regular picture of the fish. The visual cues are the 'roundedness' of the head, i.e. how steep the forehead is, and its height - something like that. Sort of like looking at something else that's round and big and estimating its 'size'.... I know people who can do this 

I'm not saying I'm good at this (although you're welcome to make me guess) - but I do think its possible, with practice and experience. 

[Angus Hulme]

Kasey, thanks, yeah not too far off...the fish in the sketch is supposed to be about 15kg, but I have to say it's hard to convey size without any additional visual reference within the illustration. At least with photos you have other elements visible, such as people, hands, lures, etc etc to give the impression of size.

Anyway, do you think the forehead of a GT is steeper, and more rounded on bigger fish, or in fact the opposite?

This is a interesting topic for me, given that I am in the process of another illustration at the moment, and really wrestling with impressions of fish size.

Cheers
Angus

[Kasey Leong]

Hi Angus,

Hey, that's not too bad, considering there's no referrence points for the sketch!

I think the forehead gets steeper, and sets much higher above the eye. For example, a 50kg Gt would have a more rounded head than the 65kg GT picture Luke just put up. That fish has a huge amount of meat sitting above its eyes!

Another example is the GT popping logo - I would say the GT in that looks like a 100-lber.

[Jay Burgess]

Interesting theory Kasey, but leaves a little too much interpretation.

I guess the overall shape of the GT as a whole can give you a rough idea, not specifically the head.