The bluefin trevally is the mighty mini-me of the giant trevally.
And—because of their tendency to hunt in packs—these fish are often more fun to catch than their big cousins. As one fly fisherman stated, “they swarm and attack flies like a pack of starving wolves.”
So, let’s check out catching this underrated bluefin trevally on a fly!
All About Bluefin Trevally
The bluefin trevally—also known as the bluefin jack, spotted trevally, bluefin kingfish, omilu, or blue ulua—is a beautiful fish that fights tough and tastes sweet.
They are found in tropical waters of the Indo-Pacific, ranging from Japan to Australia and Africa to Mexico. They inhabit inland and offshore waters ranging from bays and estuaries to shallow reefs or drop offs.
And, like giant trevallies, they are part of the jack family. While smaller–up to 35 inches and up to 65 pounds–these tough predators are a popular sport and commercial fish.
Although they are shaped similarly to a GT, they display stunning coloring that makes them one of the most beautiful fish in the ocean. Even scuba divers stop to marvel at their beauty.
Their dark greenish bodies have electric blue and black spots and markings. Their dorsal fins are the same, nearly fluorescent blue. And their pectoral fins range from a sunny yellow to a translucent sea glass green.
The bright blues make sighting them from the surface easier. Plus, their dramatic markings make them very photogenic partners when bringing one in.
Juveniles are more muted and have to grow into their flashy colors.
Bluefin trevallies are fast and fierce predators, always on the hunt. They will aggressively attack or ambush smaller fish, squid, and crabs. But they are also quite opportunistic—their pride doesn’t get in the way of scooping up the free-floating scraps left behind by larger predatory kills.
They are insanely strong and, pound-for-pound, may even out-fight their bigger cousins. Adding to the allure of targeting them is their tendency to school and create frenzied feeding attacks.
While schooling is normally seen by younger bluefin trevally, adults also school. Sometimes for spawning—which they do up to eight times a year—or for hunting. Studies have indicated that their congregations may be tied to the release of chemical dimethylsulfoniopropionate (DMSP) from the reef.
Where to Find Bluefin Trevally
Bluefin trevally are distributed throughout the Indo-Pacific regions and inhabit a wide range of inshore and offshore habitats, from sand flats to offshore reefs.
Juveniles spend most of their time in the inshore waters. Here, their diet is predominantly crustaceans and cephalopods. The young fish find protection by ganging up and swimming in schools.
But they are fiercely predatory, and as they grow, they tend to become more solitary and venture out to deeper waters. Here their diet shifts to a primarily fish-based menu, though a crunchy crab or two isn’t rare.
However, their opportunistic personalities have them riding back into the shallows on rising tides to grab easy meals. And they can still often be seen gathering to hunt in a formidable pack both inshore and offshore.
Picking the Right Location
Heading out with bluefin trevally on your mind, you are hoping for a sunny day. You want to see the fish. And the fish wants to see its prey.
If you’re fishing the protected flat waters, the biggest bluefin trevally will be patiently waiting on the edge of your lagoon. When the tide turns and begins to push in, be prepared. They will be entering the waters ready to hunt.
You’ll find a similar pattern if you’re fishing from the reef or just offshore. When the tide starts to push, bluefin trevally, along with other predator fish, will be waiting and ready to get back on the reef and eat.
To go after the fish hunting midwater, position your boat just before the drop-off for casting. Bluefin trevallies like cool, clear water. When the shallow waters get too heated or stirred up, you’ll find them here.
Packing the Tacklebox
The reality is there is a good chance you might go after several species on any day. And since bluefin trevally inhabit a wide range of locations that other target species inhabit—like calm lagoons or deeper bommies—they are almost always a possibility.
Bluefin trevally often come in while you’re targeting bonefish. Or you might have your sites set on a giant trevally but can’t ignore the irresistible lure of a school of blue trevallies more than eager to fight over your fly.
Here’s what you’ll need for an ideal bluefin trevally fly setup.
Rods—a 9-weight fly setup is the lightest recommended, but a 10 to 12-weight rod is much preferred. It’s about finding the balance between a fast-action rod and one that will have enough power to control the fish and keep them out of the coral structures they’re going to bee-line for.
Reels—need to hold enough line for a good run and have a strong enough drag to stop these powerful little fish.
Lines and Leaders—grab a 40 lb fluorocarbon, and a 20 lb tippet for sandier bottoms, but up to 60 lb tippet in areas strife with coral croppings. They aren’t too put off about a leader, and you’ll likely need it. Make sure your hooks are up to the challenge, these are mighty-mighty powerful fish, and a broken hook is a sad way to lose one.
Flies—bluefin trevally will take your bonefish fly or your giant trevally fly. But, when given the opportunity, make some adjustments. Swap out your 6-8 in GT flies for 4-5 in. Unlike yellowmargin triggerfish, they aren’t overly picky. They’ll be attracted to various flies and colors—black, white, chartreuse…
Anything resembling fish, like small mullet, bonefish, or wrasse, work. Crab and squid patterns are successful, too.
Choose something you can move fast, and remember, they have better eyesight than GT. If using light poppers, pack extra because they will tear them up.
Tips for Catching Bluefin Trevally on the Fly
Bluefin trevally can quickly show you who’s boss on the reef. Here are a few tips to keep the upper hand.
Strip fast. If there were only one tip to give, this is it.
Don’t let your fly linger even when you find yourself with a frenzied feasting match. Sometimes the fish get so wrapped up in fending each other off that none of them reach your fly.
If this happens, snatch it back and try again—fast. If your fly settles, they’ll quickly see it is not acting “normal” and lose all interest.
In shallow waters, you can cast by sight. Quickly stripping right in front of your fish (or in the school). Offshore, blind casting can work. The bluefin trevallies often hang out below, waiting to ambush a few reef fish, but they have great eyesight and will notice what’s happening on the surface. Bird action can also signify bluefin trevally are in the area .
Once hooked, hang on and do everything you can to not let your fish cut you off on the coral. It’s their special talent. Also, the stiffer your rod, the shorter the fight.
To give them the best chance of survival after their fight, hold them into the current and let the flow go through their gills. These fish, as aggressive as they are, are relatively tame when handled, so you have time, and this can give them a chance to remain the predator they are upon release.
Newsworthy Notes About Bluefin Trevally
Bluefin trevally, or Omilu in Hawaii, is an important fish in the community. It is prized as a delicatessen, and because it can be caught near shore, it is an important food source for locals. Commercially over 700 lbs per year are caught in Hawaii.
However, the bluefin trevally population in Hawaii, especially of nearshore stocks, has seen devastating drops. Over 300% in the 1990’s alone. And the numbers have not recovered. Sadly most bluefin trevally sold in Hawaii is a result of importing it from other Pacific locations.
Because of its community importance and its struggling populations, there has been considerable focus on breeding bluefin trevally in captivity. There have been promising results with a fast growth rate and low mortality rate.
Because of the concerns about the health of this fish’s populations, many eco-conscious anglers catch and release bluefin trevally—even in areas with no restrictions as they play such an important part in local cultures.
Fishing with Scout Boats
Bluefin trevally are special to catch on a fly. They have a fight and furiousness about them that is undeniable.
But they aren’t the only sportfish in the sea—and getting out on the water to catch the most sought-after catch in your area takes the right boat.
Whether you head for the flats or far offshore, having confidence in your boat makes all the difference.
Scout Boats has been manufacturing top-of-the-line powerboats for three decades.
As Scout’s Steve Potts says, “It’s about having the very best fit and finish, strength-to-weight, performance, looks and ownership value we can possibly provide to each and every one of our loyal customers.”