The Short Answer
Longtail tuna are schooling fish that show up reliably when the conditions are right — and in Thailand, those conditions arrive on a broadly predictable seasonal schedule. December through March is the Andaman prime time, with schools moving through on bait-following migrations along the offshore current lines. September through November is the Gulf of Thailand window, when northeast-wind-driven bait concentrations bring schools in from offshore. Both coasts produce excellent longtail fishing when timed correctly.
The Andaman Season: December to March
The Andaman coast's northeast monsoon season — running from November through April — is when the offshore conditions that longtail tuna prefer are most reliably present. Calm seas, warm clear water, and strong surface bait activity create the environment where schools form and feed aggressively.
December is when fishing truly settles into a rhythm. Schools are moving, bait is concentrated near current edges and around reef structures, and the bite can be explosive. The window from December through February is the most dependable period for consistent encounters. March remains very good, though some years see the schools dispersing earlier as water temperatures shift.
Key Andaman locations include offshore areas west of Phuket, the open water around Khao Lak, and the approaches to the outer reefs. Schools are genuinely nomadic — they can be over a reef edge one morning and five kilometres offshore the next — which means local knowledge and a skipper who reads birds and current is invaluable.
Longtail tuna schools often share water with other pelagic species. A surface boil that looks like longtail can hold Spanish mackerel, queenfish, or even juvenile yellowfin. Bring versatile light tackle and be ready for the unexpected.
The Gulf of Thailand Season: September to November
On the Gulf side, longtail tuna follow a different timeline dictated by the Gulf's seasonal bait movements. September is the month when northeast winds begin establishing, pushing surface bait along the Gulf's western shore and concentrating pelagic species in accessible areas.
October is widely regarded as one of the best months in the Gulf for schooling pelagics including longtail tuna. The bait is thick, the fish are active, and the northeast wind has not yet built to the point where it disrupts conditions. November remains productive and, in good years, the run extends through early December before the Gulf side quiets down.
Gulf locations producing longtail tuna include the waters around Chumphon and Koh Tao, offshore structure near Koh Samui, and the open water between island groups. Pattaya and the eastern Gulf also produce fish during this window, with tuna following bait down the coast.
Following birds is the fastest way to find longtail tuna in Thailand. Where terns are working the surface in numbers, there is almost always something driving bait from below — and longtail are often the culprit.
The Schooling Behaviour That Makes Them Catchable
Longtail tuna are obligate schoolers during their feeding phases. Unlike solitary ambush predators, they hunt cooperatively — driving bait schools to the surface where individual fish pick them off from below. This behaviour is what makes them visually detectable and, when you find a feeding school, spectacularly catchable.
Bird activity is the primary search tool. Terns and frigatebirds gather over feeding schools, diving on the bait that the tuna push up. On flat-calm Andaman mornings in January, you can see these bird clouds from several kilometres away. Motoring toward active birds and cutting the engine before reaching the school — to avoid spooking it — is the standard approach.
Surface boils are the second indicator. Feeding tuna leave a characteristic churning disturbance on the water surface, often accompanied by flashes of silver as bait fish scatter. Early morning and late afternoon are the most productive times, as schools feed more aggressively in lower light.
Methods That Work
Casting is the purest and most exciting method. Light spinning gear in the 15–25 lb braid range, loaded with a small metal jig, chrome slice, or stickbait, is the standard setup. Cast beyond the leading edge of the school, retrieve at speed through the feeding zone, and hold on. Longtail tuna punch well above their weight in terms of initial run and sustained fight.
Trolling small lures through active bird activity is a reliable method when schools are moving and difficult to approach closely. Small Rapalas, feather trolling lures, and squid skirts in natural colours work well. Keep speeds moderate — 5–7 knots is typically effective.
Unweighted live bait — small garfish, sardines, or mackerel — cast into or near a feeding school produces aggressive strikes and suits anglers who prefer bait fishing. This method also tends to target the larger, more cautious fish sitting at the edges of the school rather than the feeding frenzy at the surface.
For charter options targeting longtail tuna and other schooling pelagics, see our guide to light tackle charters in Thailand.
Setting Expectations
Longtail tuna in Thailand typically run between 3 and 8 kg in the schools most commonly encountered. These are not the giant yellowfin of deep offshore water — they are high-volume, fast-action sport fish that deliver exceptional fight-per-kilogram performance on appropriate light gear. On a good day, a productive school can yield a dozen or more fish to the boat before conditions change.
Larger individuals above 10 kg exist, particularly on the Andaman coast during the peak months, and these fish tend to be found sitting deeper or at the edges of large schools rather than in the surface-feeding melee.
Plan Your Trip
For full species information including identification, habitat, and tackle recommendations, visit the longtail tuna species page. For a complete view of what each month offers across both coasts, see our best time to fish in Thailand guide.
