The giant trevally inhabits a very wide range of offshore and inshore marine environments, with the species also known to tolerate the low salinity waters of estuaries and rivers.
The species is most common in shallow coastal waters in a number of environments, including coral and rocky reefs and shorefaces, lagoons, embayments, tidal flats and channels. They commonly move between reef patches, often over large expanses of deeper sand and mud bottoms between the reefs.
The species predominantly takes various fish as prey, although crustaceans, cephalopods and molluscs make up a considerable part of their diets in some regions. The giant trevally employs novel hunting strategies, including shadowing monk seals to pick off escaping prey, as well as using sharks to ambush prey.
It is not uncommon to hook giant trevally whilst trawling for tuna, wahoo and sailfish in the deep blue. It has been noted that GTs have been caught in water depths exceeding 80m. On the extreme opposite side of that, as fly fishermen, the most appealing way to hook a GT is in knee-deep water wading the flats. This just proves that they are an apex predator which hunts from the deep waters around the islands to the lagoons and shallow flats of all the atolls.
Upon seeing a giant trevally, it is crucial to remain calm. Listen to your guide. Move into position quickly whilst trying not to make too much noise and keeping your fly line clear of any potential snags. Under the guide's instruction make the cast. Leading the fish by 3 - 4 rod lengths is the general rule. If the fly lands on the head or behind the GT, the chances of the fish eating it are almost none. Once the fly has been presented and all is still well, a long and fast retrieve is necessary. Once the fish eats the fly, keep the rod tip pointing down, and set the hook by strip/line setting. Lifting the rod in an attempt to set the hook will not be effective and is a sure way to get the hairs on the back of your guide’s neck to stand on end. Only once the giant trevally is on the reel can you lift the rod and fight. And to be clear, you will need to get ready for one hell of a fight!
A similar approach to giant trevally fly choice can be taken as with big Barracuda. The fly choice should be dictated by the area you are fishing and the bait species that inhabit that locality. Brush flies, sempers and poppers are all effective. As a general rule, lighter coloured flies should be used on the white sand e.g. tan and white, as these lighter colours are more representative of species such as mullet, small trevally and bream. Darker coloured patterns are more suitable for surf areas and coral fingers e.g. red, black, and brown, making a realistic impression of various types of reef dwellers, grouper, snapper and emperors.
Fly fishing is an art form that not everyone can master. It takes skill, patience, determination and knowledge. The right rod will take you a lot closer to landing the catch. Everything about GTs are big! Big fight, big flies, big fish, so naturally a big rod is needed. 12 Weight fly rods are therefore used to target giant trevally. This needs to be paired with a high-quality large arbour saltwater series reel with a strong smooth drag to match the 12-weight fly rod. The reel should be loaded with three hundred yards of 80 lbs braid. Once hooked, these fish love to head straight for the coral or drop-off into the deeper water which very often results in a lost fish. Having a rod that you can pull very hard is very necessary, and therefore any rod with a strong butt section is recommended.
A pushing tide is considered to be the best time to target giant trevally. This is because the fish know that they have plenty of water pushing behind them on the flats, and are more at ease as to not get trapped, as opposed to a dropping tide. As the cool freshwater flows onto the shallow flats many invertebrates such as crab, shrimp and worms leave their holes. This, in turn, brings bonefish and other small fish onto the flats to feed and the chain continues up to the bigger predatory fish like the giant trevally.