Arguably fly fishing’s most loved saltwater bullies, there’s a lot more to Giant Trevally (Caranx ignobilis) than meets the flats angler’s eye. To understand these incredible fish a little better, in issue 31 we spoke to three leading fisheries biologists about their work on the world’s biggest Giant Trevally aggregation off Mozambique, why South Africa’s coastal GT fishing has deteriorated so much and just what the hell GTs do at the fabled Eastern Cape estuary of Mtentu.

Think of “Giant Trevally” and what comes to mind is probably a massive, kingfish-destroying bonefish on a Seychelles flat, or maybe the plus-size specimens caught in the seas off Oman. Narrow down your brain’s search engine to “Giant Trevally from Sub-Saharan Africa” and your results thin out a bit. There are the small GTs caught occasionally in estuaries and off the rocks along the Wild Coast, but for adult GTs you would have to concentrate your attention on northern KwaZulu-Natal where fabled destinations like Kosi Bay mouth and Rocktail Bay were put on the map by this species. In the ‘80s and ‘90s, the GT fishing was incredible in these places but, despite the odd large fish being caught every now and then, additions to “The 100 Club” (fly anglers who have caught a 100cm+ GT on foot on the South African coast) are increasingly rare.

“It’s very disheartening because, in the 80s and early 90s, you’d catch big giant trevally there.”

Someone who saw this area in its heyday is Andy Coetzee, one of the pioneers of GT fishing along the Northern KwaZulu-Natal/ Maputaland coast that borders onto southern Mozambique. Andy still works in the area, running diving tours and guided walks from Kosi to Sodwana, but his interest in fly fishing for GTs has waned as the fishing has deteriorated.

Andy says, “I started fishing Maputaland from about 1984 through to the early ‘90s with a fly rod and a heathen stick with poppers and live bait. I would go down to Kosi mouth and throw poppers and I would be guaranteed to hook at least two or three fish – anything from the range of 15-30kg. There were lots of greenspot kingies and the Ignobilis, the GTs. The numbers that used to be there were absolutely phenomenal. I can remember going to Rocktail Bay on a spring high tide in the afternoon… eight casts, eight bust-ups, packed up and went home. That’s it.”

Andy Coetzee with a Giant Trevally caught in northern KwaZulu-Natal

Andy Coetzee with a Giant Trevally caught on the northern KwaZulu-Natal coast in its heyday.

“However, since then I’ve seen the decline. In 2014 and 2015 I went to Bhanga Nek with my brother and we fished the prime times, 3:30 am to 5:30am, prime light both in the morning and afternoon. We used a fly stick as well as a big stick, throwing poppers, surface lures and stick-baits. Nothing! It’s very disheartening because, in the 80s and early 90s, you’d catch big fish there. The kingies would smoke you, charge in right between your legs.

“The kingies would smoke you, charge in right between your legs.”

“I remember seeing shoals of big kingies chasing mullet and the mullet were jumping out of the water. You could pick them up, pin a 9/0 through a mullet’s arse and in three seconds you’d be tight. Those days are gone. You don’t even see mullet coming into Kosi mouth. I seldom pick up a fly rod anymore, because the effort to go and have one pull is hardly worth it.”

While die-hards will continue to fish these areas and occasionally get a positive result, it’s easy to understand why Andy is so despondent. His experience is anecdotal, but it’s still an important baseline to remember because as humans we’re adaptable (just compare the idea of a national curfew today to the same idea two years ago). A good day out fly fishing for GTs in northern KwaZulu-Natal today looks a lot different to a good day out for Andy and his fellow pioneers back then.

Fortunately, it’s not quite time to slit your wrists when it comes to the future of GTs along our coastline. That frisson of optimism is thanks to a special annual event that fisheries scientists have been studying for the last six years. Each year at a very specific time on a very specific moon in a very specific place off the Mozambican coastline, Dr Ryan Daly, Dr Tess Hempson and Dr JD Filmalter and their colleagues come together for an orgy of Giant Trevally.

A good day out fly fishing for GTs in northern KwaZulu-Natal today looks a lot different to a good day out for Andy and his fellow pioneers back then.

“Aggregation” is the scientific word for it, but to a layman that sounds a little too much like an Excel shortcut. Regardless, what makes this aggregation so special is that it’s the biggest aggregation of GTs on the planet. Where most GT aggregations from Hawaii to the Philippines and the Seychelles number in the hundreds, the southern Mozambican aggregation has been estimated at 5000 adult fish. That equates to 30 tons of adult Giant Trevally with some individuals estimated at 56kg.

Dr JD Filmalter with a Giant Trevally from the Mozambican aggregation

Dr JD Filmalter with a Giant Trevally from the Mozambican aggregation. Photo Paul Cowley

The data gleaned gives us more insight into the secret lives of GTs than ever before. We sat down with these scientists to discuss what they have since learnt about GTs. Why the once-famed GT fishing in South Africa is now so poor. And, just what the hell is going on at the fabled estuary of Mtentu on South Africa’s Wild Coast.

Read the rest of this story and plenty more in issue 31 of The Mission below. As always, it’s free.