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Topwater Caranx Ignobilis: Giant Trevally (GT) => Reports & Expeditions => Topic started by: Trevor Skinner on June 09, 2013, 02:50:32 PM

Title: Black GTs are like London Buses...
Post by: Trevor Skinner on June 09, 2013, 02:50:32 PM
....you wait for ages for one and two turn up at the same time.

After a succession of bright silver fish at last a couple of big black mamas (down Luke)




Regards,


Trev
Title: Re: Black GTs are like London Buses...
Post by: Nathan Tsao on June 09, 2013, 03:08:32 PM
its kind of strange to me that i notice a bunch of guys here on the forum say that the black GTs are hard to come by. It must have a lot to do with location, because i think that 75% or more of the GT's that i see here in Kona are the blacker ones.

I wonder why it is that they are more rare in other parts of the world???

Nice Fish Trevor!!!
Title: Re: Black GTs are like London Buses...
Post by: Trevor Skinner on June 09, 2013, 03:19:45 PM
Nathan,

I wish they were easier to put alongside the boat! That last fish gave me some real hurry up.

I've asked this question of a few very, very experienced GT fisherman and there seems to be as many answers. What I have noticed is some fish seem naturally black even when chasing the lure while others seem to darken up after hook up and capture. Both these fish were mottled and darkened up considerably after capture.

I've seen both black and silver fish in both Musandam and Halaniyat. The darker fish seem less common but don't have any real numbers.

Regards,



Trevor   
Title: Re: Black GTs are like London Buses...
Post by: Mark Harris on June 09, 2013, 03:32:57 PM
I have seen three theories on this:

1. The VERY dark ones are breeding males. This makes sense in areas where you do not see many and also where those you do catch seem very pumped up and aggressive.

2. Pigmentation from specific diet. This makes sense in areas like Hawaii and parts of the South Pacific where black GTs seems to be the norm rather than the exception.

3. Colour change during hunting (as with some scombrids like sailfish, wahoo etc.). I am not at all convinced about that for GTs.
Title: Re: Black GTs are like London Buses...
Post by: Andy Rowe on June 09, 2013, 04:26:34 PM
Some more input;

Mark, agreed with your point 1, black ones go harder, testosterone is probably a key ingredient to increased aggression and strength at least in the areas around Indonesia from my experience. The darker fish are not as common in the Indonesian fishery and I note the black ones generally fight 5-10kg above their weight.

point 2, that is interesting, also consider camouflage, the dark basaltic rocks of hawaii and Eaio appear to produce a disproportionate number of dark fish, perhaps the darker coloration here is a result of natural selection where darker fish are more successful in ambush situations. Or it may be a case where the fish can readily change colour to match the back drop. Interesting to note also are localised dark spots in lighter coloured fish, this appears to be related to areas  where the lure has rubbed on the fishes face.

It's an interesting point and I think there may be several reasons for dark fish but I'd presume the case of the inordinately strong + black fish to be males.



Title: Re: Black GTs are like London Buses...
Post by: Mark Harris on June 09, 2013, 04:44:44 PM
Good points Andy.

The camouflage and diet points may be related - i.e. the need for camouflage against those dark basaltic rocks is met by something specific in the diet.

I also forgot to mention some anecdotal evidence for the breeding males theory. I can remember several occasions when a very black GT I caught has been very milty.  I know others have mentioned this as well.

Title: Re: Black GTs are like London Buses...
Post by: Ed Nicholas on June 09, 2013, 06:56:45 PM
Awesome fish Trev. We landed way more Black Geets through April than at any other time of year down here and alot of them were heavily laden with sperm often squirting it out on deck adding to the projectile vomit, sh*t and slime that covered us from these beasts.

Is there really no information around on identifying M/F GTs, age of the fish etc? I find it astonishing that there are so many of us chasing these fish yet we know pretty much sweet F-A about them. We can find hundreds of threads on how to catch them, the best lures etc but info about the fish themselves is like gold dust.
Title: Re: Black GTs are like London Buses...
Post by: Trevor Skinner on June 09, 2013, 07:08:29 PM
Ed,

Seriously, if Mark can't control his bodily functions and keeps making a mess of your boats like that you should ban him. It's just not polite let alone unhygenic.




Trev



 
Title: Re: Black GTs are like London Buses...
Post by: Ed Nicholas on June 09, 2013, 07:13:06 PM
Haha thats gold  :)
Title: Re: Black GTs are like London Buses...
Post by: Mark Harris on June 09, 2013, 07:14:01 PM
Even I will admit that is very funny! :)
Title: Re: Black GTs are like London Buses...
Post by: Mark Harris on June 09, 2013, 07:25:43 PM
The harry monk all over my shirt in this pic has absolutely nothing to do with me though.

(https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-ash4/423706_178077085640073_797920198_n.jpg)
Title: Re: Black GTs are like London Buses...
Post by: dante green on June 09, 2013, 07:35:23 PM
....you wait for ages for one and two turn up at the same time.

After a succession of bright silver fish at last a couple of big black mamas (down Luke)
Sorry to tell you this, but those aren't black gt'ss. Black gt's has a deeper slant forehead.



Regards,


Trev
Title: Re: Black GTs are like London Buses...
Post by: Mark Harris on June 09, 2013, 07:41:38 PM
Dante - a black GT is not a species.. it is a colour variant of GT.

If you mean Black Trevally (caranx lugubris)...... that's a completely different species of fish and is not being discussed here.
Title: Re: Black GTs are like London Buses...
Post by: Trevor Skinner on June 09, 2013, 08:37:43 PM
Awesome fish Trev. We landed way more Black Geets through April than at any other time of year down here and alot of them were heavily laden with sperm often squirting it out on deck adding to the projectile vomit, sh*t and slime that covered us from these beasts.


Ed,

On second thoughts and to save considerable embarrassment to Mark, you could rename your boat 'The Barasti'


Trev
Title: Re: Black GTs are like London Buses...
Post by: Nick Bowles on June 10, 2013, 02:02:23 AM
Eish Mark think you caught the wrong end of the stick there! Think I remember seeing Mr Luke with an excited GT as well trying to blame the poor fish!

Same story as where the big GTs come from, black GTs are a bit of a mystery and seems to be something to do with spawning in Oman but then in Seychelles almost all of the fish are silver/white so also think the whole environment they hunt in is a factor to some extent. Chameleon type scenario. Seychelles mainly white flats very silver almost white GTs, Oman/Hawaii/Tokara deep water with volcanic or dark structure and the fish are generally darker. Agree with Ed, there is a lot about fishing for GTs but not much we now about them! Hopefully we can understand them more in the future!

Another good one to discuss around the fire!

Cheers,
Nick
Title: Re: Black GTs are like London Buses...
Post by: Nick Bowles on June 10, 2013, 02:15:50 AM
Trev the black GT goes well with the hat, nice accessory! Well done on two great fish this last weekend!
Title: Re: Black GTs are like London Buses...
Post by: Nathan Tsao on June 10, 2013, 03:00:14 AM
Pretty much the entire coastline of Big Island is black porous lava rock, perhaps there is some degree of camouflage benefit for many GTs being darker here. Some of the fish are even as dark as the rocks themselves!
(http://imageshack.us/a/img801/8596/dscf0603u.jpg) (http://imageshack.us/photo/my-images/801/dscf0603u.jpg/)

Uploaded with ImageShack.us (http://imageshack.us)
Title: Re: Black GTs are like London Buses...
Post by: Mark Harris on June 10, 2013, 09:38:25 AM
Nathan, that is a truly superb photo.
Title: Re: Black GTs are like London Buses...
Post by: Nick Bowles on June 10, 2013, 12:16:56 PM
Nice fish and loving that its caught on conventional, good skills!
Title: Re: Black GTs are like London Buses...
Post by: Andy Rowe on June 10, 2013, 06:05:15 PM
Take from this what you will on the colour question, still not definitive but getting close.....

http://www.readcube.com/articles/10.1038/178934a0
Title: Re: Black GTs are like London Buses...
Post by: Mark Harris on June 10, 2013, 11:41:41 PM
Very interesting Andy and well dug out.

In summary, that is saying that sexual predictions based on colour were correct in 90% of cases in the East African population surveyed.  And in the mature examples, (70 cm or longer) close to 100% correct.

That is pretty strong evidence at least for that particular population.
Title: Re: Black GTs are like London Buses...
Post by: Ed Nicholas on June 11, 2013, 01:19:16 AM
Sick picture man.

Loving the detective research Mr Rowe. Thats exactly the sort of survey that we need more of but look at the date .. 1957!! Guys were doing more then than we are now, crazy.
Title: Re: Black GTs are like London Buses...
Post by: Andy Rowe on June 11, 2013, 10:50:59 AM
Men, thats only a snippet of the original paper, the abstract i think. The original you can pay for in Nature magazine if anyone is really keen but i think that distills the main point. There is more info on the net. The same question came up a some years back on this forum and i remember reading one paper from a study in Hawaii which claimed capture of a hybrid giant and bluefin trevally!!

 I still think the males have the ability to go from dark grey on top to really dark (black) when they are stressed, angry or in mating mode. In places like hawaii and the marquesas where the background structure is dominantly dark basalts; a silver fish in ambush would stick out like you know what; so perhaps in these localities the females also have the ability to pigment dark. This theory is just based on observation and a rudimentary understanding of fish biology though.
Title: Re: Black GTs are like London Buses...
Post by: John Cahill on June 11, 2013, 06:19:22 PM
The black ones I have seen have all been milting so they must be males that are 'ready to go' in my humble opinion! :o
Title: Re: Black GTs are like London Buses...
Post by: John Cahill on June 11, 2013, 06:21:29 PM
The harry monk all over my shirt in this pic has absolutely nothing to do with me though.

(https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-ash4/423706_178077085640073_797920198_n.jpg)

hehehehe ;D
Title: Re: Black GTs are like London Buses...
Post by: Alex Jordan on June 11, 2013, 07:16:02 PM
Mark that is a great picture - spat my morning coffee out!!!

We had a 4 way black pack attack on the Weds night during our trip that saw Nick and myself hooked up - mine pulled and Nick landed a nice black beauty ... definitely on my wish list to achieve this year!

Nathan - great picture dude!!
Title: Re: Black GTs are like London Buses...
Post by: Mark Harris on June 11, 2013, 07:23:02 PM
It was a very affectionate fish  8)