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With the kind assistance of the
New South Wales Department of Primary Industries
(NSW DPI) we have
started a programme here around Kadavu Island to Tag and Release
primarily Dogtooth
Tuna
but also some Giant
Trevally
caught and released aboard our gamefishing boats Bite Me and Tease Me.

Our first Tagged GT measured 37" Short Length and weighed 16kg

Our second GT Tagged measured 46" Short Length and was estimated to weigh
35kg

Tag placement

We also tagged our first Dogtooth Tuna of 15kg but no photos - a quick release...

Although it is believed that GTs and to a certain extent Dogtooth Tuna are terratorial and spend much of their adult lives
staking out their particular patch of reef, relatively little is known
about them. We hope to shed light on the following grey areas :
  1. Release mortality rates - GTs seem to be very hardy fish but how well do they really release ?
    Dogtooth tuna are monsterous brutes but do they survive a fight ? Does invisible barotrauma affect release
    mortality rates ? Do release weights improve the chances of a healthy
    release ?
  2. Movements - Do these species move significant distances ?
  3. Growth rates.

It will take a while to get recapture information but we are optimistic...
Last month we caught the same GT two days running, in the same place, on the same lure....
Obviously its first days encounter with anglers didn't seem to cause the fish any great
disruption.


Views: 257

Replies to This Discussion

Aloha Scott,
Roberta from Makaira Resort here. We have been part of some pretty extensive research with the Taveuni GT's and Gt's in general, since we have such a deep love for the fighting spirit of that species. . I can answer some of your questions that have been answered by Clay Tam who heads the GT research foundation in Hawaii.

We are just a couple of GT's away from releasing a 1,000 GT's. They are ideal species for releasing because they are very hearty, ( as our sailfish) can survive a quick photo op and measurement for weight and be released. Out of almost a thousand releases only one didn't make it because the hooks went too far down the throat and cut a major artery. We were so disappointed because we take GT releases pretty serious for the following reason. It is important to release GT's aside from the possibility of ciquatera since they are reef feeders is their growth rate. If more people knew this information they would be much more likely to release them At 27 inches they become sexually viable. However, once they hit that stage they grow on average only an inch a year. So they are an extremly slow growing fish. Any species that grows that slowly needs to be released. Probably the area that is least known about GT's is their mating habits. Which is all the more reason to release them, if an area is stripped clean of GT's it will remain so for an indefinite amount of time.

As you probably already know when you release them you must actually drop them in head first, so the water can quickly flow through their gills and then they are off like a shot and fit and fine. Setting them gently in the as one would when releasing a sailfish or billfish where you need to sway them back and forth in the water using their tail to get the water through their gills and once you see color they are ready to go, this does not work as effectively for GT's who need that sudden gulp over their gills.

We never put a tag in the fish because it will risk infection, or it could get snagged on the reef and tag information is up for general information, so a commerical fisherman can come into an area knowing there have been a number of fish tagged there and wipe it out. I have seen a couple of good spots decimated by the midnight foreign longliners. Very sad indeed, in fact it is heart breaking.
Although they are basically territorial, they have been know to range 14 miles and occasionally up to 30 miles through island chains. Their migration depends on food supply, mating season and overall health of the reef. I would also guess that if an area became inundated with some large predators they also may range out and look for greener pastures.
Over the last two years we have contributed 50 fin samples to the Hawaii GT Research lab to try and ascertain why the Taveuni GT's are so gnarly. In a brief analysis they came out pretty much the same as the Hawaiian species and their strength may be attributed to their health from living in abundant waters and working the stronger currents in Fiji.
The latest DNA analysis of white GT's have demonstated that about 6% of the Hawaiian population has crossed with the Blue Fin Trevally via the female. THe hypothesis is since GT ocean spawn and hope for the primodial hit of eggs and sperm meeting that for some reason the female blue fin eggs are pretty compatible with other species of GT's. So if you happen to catch a GT which doesn't quite look right please take a photo and we can see if that same cross is occuring in Fiji.
We have seen large groupings of GT's of schools up to 100 that usually occurs during the birth of the reef. So it is my guess that they are trying to congregate to give the primodial soup hook up a better ratio, much like Salmon but to a lesser population degree. Also a heavy dose of pheromones in the water helps to get things moving along.

So my question for you is how are you releasing the Big Dog tooth tuna? We have had very little luck at their survival rate once they have passed a 100 lbs since they are coming up from such great depths on jigs, they are pretty wrecked by the time they reach the surface with a good case of what I call the bends. We really want to be able to release them back into the wild and preserve them like we do the GT's.. The smaller ones seem to do okay or if they were caught trolling they do all right. But we have had little success with the big ones that are jigged up.

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