What do you think about this paper?

[David Lumanauw]

http://link.springer.com/content/pdf/10.1186%2Fs40317-015-0024-0.pdf

[Hamad Alroumi]

thank you David for this interesting paper , I did statistics  at the university during and I was good at it.
ill send this paper to my professor and ill schedule a meeting with her to discuss it,

and interesting fact that at some reefs the GT had more activities at night , that might be influenced by the full moon effect
and some reefs had more detection during day time ,

I don't know if they included the currents or the moon phase in the study as far as I know it affects the activities of the GT,
An interesting Fact that GTs don't leave the territory after being released , not like the sailfish they tend to leave the area once they tagged and released that's why they used a different approach to tag them using a speargun with a satellite tag-head which worked really well and the sailfish remained in the same area.

this kind of info will really help us to find Gts ! thanks a lot again david

tight lines !

[Trevor Skinner]

The conclusions are interesting although much of the sampling detail is lost on me these days.

I remember reading an Hawaiian study done some time ago that came to the opposite conclusion. It fundamentally concluded that GTs range over a wide area.

My only experience in this regard is anecdotal. Ed Nicholas from No Boundaries in Oman has been dart tagging GTs in Southern Oman for some years, in that time there has been relatively few recaptures. Either of two things are happening: 1. There's an extremely high mortality rate 2. The fish are moving somewhere else. The reefs are generally still very healthy and given that they are pressurized by local net fisherman from time to time they repopulate relatively quickly. Either there is a huge population of very large GTs and the fatalities don't matter or the fish are surviving and moving away, at least for a time. I suspect the latter. 

The other piece of evidence also revolves around Ed's initiative to put two 30 day pop up tags on a couple of big GTs. If I remember rightly, one moved to a reef within the same system but 30+km away and the other moved away from the reef system all together. Both fish survived, at least past the 30 day mark by the way. The interesting thing was that both fish spent considerable time at depths around 80metres. It's also worth noting that most of these fish were much larger in size (length and kg) than the sample taken in the GBR study.

Regards,


Trevor     
   

[David Lumanauw]

I also read the Hawaii paper, as I remember it contradicts with this paper about the depth range that GT spend. In Hawaii papper, GT spends time at 100m deep, seldom go to less than 50m depth. This maybe because of the capture method is different.
GBR GT's are captured around shallow water with artificial lure (popping?)
Hawaii GT's are capture with bait to 100m depth

Hi, Hamad,
What is the meaning of figure 2b? What is mean depth (sqrt m2) ?
Corelating environmental factors for GT whereabouts are in table 3.
Light intensity, water temperature, winds speed determines where the GTs are.
Moon illumination (moon phase?) has little corelation

Night time popping should give better and bigger GTs, if this paper is correct. Anybody has tried night time popping?

[David Lumanauw]

http://www.hawaii.edu/himb/ReefPredator/Ulua.htm

This is the Hawaii study. As you can see, GTs here spend their time at 100m depth

Yellow is daytime, black is nighttime

[David Lumanauw]

About tagged GTs are seldom recaptured, also happens here in Indonesia. In Bali, some GTs are tagged after CnR popping activities. Very seldom one is recaptured.
I think GTs are smart fish. If the are captured with a surface popper, they are learning. It wont bite popper again. Stickbaits has advantages for these GTs.

In spots where CnR are the code, this happens also. In Alor, Komodo, quite difficult to get big GTs. But divers see many big GTs in that spot. They just dont want to bite popper.

[Ryan Keith]

Thanks for sharing, David. In 2013, I actually contacted some of those authors to propose a tagging study of my own; I was told they already had a student working on GTs... seems they were talking about Elodie! Small world.

I don't find this paper convincing in its conclusion that GTs show high site fidelity - the authors themselves acknowledge this a few times but still interpret the data as validating the fidelity postulate. Usable data were obtained from only 10 individuals; the other 10 could have gone anywhere (and probably did). When half of a population stay in an area and the other half disappear from an area, it is inappropriate to conclude that the population as a whole displays high site fidelity. That much is logical.

When I look at the data, they tell a story that runs through many other GT studies with small sample sizes: different fish act differently (this can be seen in the huge standard deviations surrounding most figures); as the authors state on p7, "long-term residency patterns were variable". Sadly, many generalisations in these kinds of papers tend to fall apart. Such is life. At least the authors made an effort to draw out relationships by conducting various complex statistical tests... I'm just not convinced this can compensate for the difficulties inherent in studying a small subset of a population with the biological/behavioural attributes of Caranx ignobilis.

Despite my quibble with the overarching conclusion of the paper, I think a few of the minor observations/trends are interesting to note, especially for this particular GBR population:
- Tagged GTs were detected more frequently at night, meaning they may hunt on the reefs under the cover of darkness, as do sharks.
- As light intensity increased and wind speed decreased, tagged GTs were found deeper in the water column... hence, it might be wise to target GTs around deep pinnacles and reefs during the middle of calm sunny days. This may be a particularly good tactic in Spring (vs. Autumn), and when tides are strong.
- Some tagged GTs may have spawned around the October full moon... so keep a lookout for mobile bommies at this time!
- Tagged GTs roamed around reefs in three dimensions, using some areas more frequently. These are probably foraging grounds where current flow is strongest (think of drains, points, pinnacles etc).
- Tagged GTs moved to shallow areas when winds were strong, so working the reef line on a windy day might be productive (I'm picturing New Cal here too).

That's my two cents' worth.

[Cameron Mundy]

I think GT's are like all major predators they want to get the maximum amount of food with a minimal amount of effort so they'll hunt when the conditions suit them. Obviously there's a ridiculous amount of factors involved trying to narrow down the time window when the stars align and the buggers decide they are hungry but I've found there's a few windows that are always worth putting in the extra effort especially if you can score a combination of conditions 

Dawn and Dusk, GT's love low light conditions there's a reason they have such big eyes. when we target them in South Africa from the beach with live and dead bait you have to be fishing an hour and a half before sun up and 2 hours past sun down. On live aboard trips in the Musandam and fishing from the islands in Southern Oman I've had some memorable fishing in pitch black conditions.

Tides & Moon, the two are obviously related I personally like the run up to the peak of the high tide although I have had great fishing approaching the bottom of the low the key factor is the amount of current the tide is offering. Spring tides have the most current and neaps the least, for what ever reason in the areas I've fished 3 days after springs have generally been the most productive. On a neap tide I go jigging I've found the GT's tend to sulk in the depths but are still keen to eat. I think the current lets the Geets hang around the leading edge of the reef or there favorite bommie spending minimal effort and watching what the current sweeps toward them.

Noon, I like fishing deeper areas around noon with the sun over head you get a great silhouette of the lure on the surface which can trigger hits from fish you normally won't get a shot at so if you have a reef sitting at 30 to 50 meters its worth a try you will have to do multiple passes though.

Water temp 26 deg is marginal 28 is magical 30 and more means its hotter than hell on the boat and I'd rather be trolling and drinking beer

The last thing to remember is that sometimes the fish are just arseholes and won't eat anything.     

[David Lumanauw]

A traditional fisherman told me the GTs are eating just when the water starts to move. I assume this is from top of high tide or from bottom of lowtide. Unfortunately, this time window is just about 15 minutes. After the current flows more rapid, they disappear (again)