Weighing fish

[Charles Cintron]

Howzit everyone,

For those of you that weigh your fish I was curious as to how you go about doing it while on the water? I'm talking about something over 45k. I fish from an 18' boat and would like to weigh the big boys just to get a number. We usually just measure and toss them back quickly but i'm curious as to how much they actually weigh now.

I'v only seen spring scales up to 100pounds but would at least like something up to 150pounds as I would only weigh something massive. I've seen guys on videos with a supermarket scale and plyboard but I don't think I have room for that. Is there a heavy duty boga grip out there?

Mahalo

[Luke Wyrsta]

Howzit everyone,

For those of you that weigh your fish I was curious as to how you go about doing it while on the water? I'm talking about something over 45k. I fish from an 18' boat and would like to weigh the big boys just to get a number. We usually just measure and toss them back quickly but i'm curious as to how much they actually weigh now.

I'v only seen spring scales up to 100pounds but would at least like something up to 150pounds as I would only weigh something massive. I've seen guys on videos with a supermarket scale and plyboard but I don't think I have room for that. Is there a heavy duty boga grip out there?

Mahalo

Hi Charles,

I'm glad this topic came up as I was going to post about this sooner or later.

I think the best solution is the body scales - there are digital ones available at fair prices that are very accurate.

Boat movement is always going to be an issue, but not something that can't be overcome within the same time that it takes to take various measurements of a fish.

I support the taking of fish measurements, however, I still do not find them anymore than a ballpark indicator. Historically, they haven't been very accurate in fish over 45kg as these specimens always have greatly varied girth vs length.

Fukui-San, of Tokara and World GT fame uses a scale, of which an aluminum frame perspex box is placed over the surface of the scale so that measurements can easily be seen without any fish touching the ground. A piece of ply is placed on top of the box and the whole weight of the additional assembly offset on the scale control.

I feel spring scales and bogs grips will be adverse to the health of the fish as they provide zero body and spinal support of the GT. Weighing them this way will significantly harm them and reduce chances of survival once released.

Luke

[Thien Dao]

Why not just use bathroom scales to weigh yourself holding the fish, then subtract your body weight?

[Charles Cintron]

Good points Luke two guys holding a big fish up by it's tail or mouth is definitely going to do some damage.

Thien that's  prob what I'll end up doing the problem for me is that the area I fish has some rough water most of the time and standing on a little square in a small rocking boat would be a circus act for me and the fish lol! Using that method I would have to motor out of the rough zone keeping the fish out of water longer.

I think I might rig up some scale to a net that way we can keep the fish in the water as we prepare everything. Or maybe I should just scrap the idea and just exaggerate the weight of the fish to my buddies

[Mark Harris]

Like Thien, I have always thought bathroom scales are an incredibly simply solution and I don't know why charter boats do not use them?  Holding 50 kilos of fish while balanced on a scale on a rocking boat could provide its challenges but certainly not to the extent of catching the thing in the first place!

If you are on your own, the balancing act may prove too much, as Charles suggests.

Seems a very simple solution to me for boats with more than one person aboard.

[Nicolas Lim]

I've always wondered about this. I find the estimates given by guides to not really reflect the true weight of the fish. Case in point, I was in a fish freezer in Oman and there was a GT that the guide estimated at 45 kg in there. Just out of curiosity, I put it on the commercial scales that they had there and it topped out at 28kg.

I think taking measurements of girth and length would probably be a true judge. However, for bragging rights in the pub - 45 kg is a lot more fish than 28kg. :-D

[Simon Bomholt]

Why not use a sling like the ones used for carp, pike evt. There are some monster models used for catfish that easily holds a Big gt. Look at Star bait monster sling

[Mark Harris]

Nicolas - I do agree that some guides over-call fish to the ridiculous extent that you mention with the Oman fish.

Specific length and girth measurements are much better than the guesses of a guide who may or may not experienced enough to make such calls, and at least give a fair idea of how big the fish really was.

For my own part, many I have fished with call me a miserable git for often under-calling fish, but I would rather be that way than over-estimating.  The only large GT I have ever not released was a jigged fish which sadly died despite a very long effort to revive it. That one was weighed back at the dock as I gave it to the deckies to sell at market.  I had actually under-estimated that fish by 4-5 kgs  .

Simon - I too have a bit of experience using those massive European Carp/Wels Catfish slings and they could be a good option for GTs. Setting one up on a boat though would not be easy, nor would finding the space for it.  Logistically I prefer the bathroom scales I think, unless it is a large boat with enough space to leave a sling permanently set up.

[Craig Maree]

I've always wondered about this. I find the estimates given by guides to not really reflect the true weight of the fish. Case in point, I was in a fish freezer in Oman and there was a GT that the guide estimated at 45 kg in there. Just out of curiosity, I put it on the commercial scales that they had there and it topped out at 28kg.

I think taking measurements of girth and length would probably be a true judge. However, for bragging rights in the pub - 45 kg is a lot more fish than 28kg. :-D

Did you perhaps take the fork length measurement of the dead GT?

[Doug Terry]

for the scales look here. http://www.mkscales.co.uk/products_120_27_MKS-NTA-Hanging-Scales.html
and place the GT in a carp weighsling.
hope this helps.

[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]

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!

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.