SPECIES SPOTLIGHT - LONGTAIL TUNA

LONGTAIL TUNA

BY DR JULIAN PEPPERELL, PhD.

Dr. Julian Pepperell, PhD, is one of the bestknown marine biologists in the world and a leading authority on Marlin, Sailfish, Tuna and Sharks.

THUNNUS TONGGOL The Longtail Tuna is one of the ‘true’ Tunas (complete with the first name Thunnus), that, kilo for kilo, is widely regarded as perhaps the toughest of all the Tunas on matched angling gear.

We tend to think of the Tunas as masters of the high seas –migratory nomads wandering unimpeded across the vast expanses of the world’s oceans. And while that’s true for species like Bluefin, Bigeye and Yellowfin Tuna, a notable exception to the rule is the Longtail Tuna. This is a species of tuna that instead prefers to hug the coast, spending its whole life in the warm shallow waters of continental shelves and embayment’s, never venturing into the wild blue yonder.

Back when I was a lad, the name ‘Longtail’ Tuna would have been met with a blank stare, even among anglers who caught them regularly. That’s because, since time immemorial (well, for a long time anyway) the species was always known in Australia as ‘Northern Bluefin Tuna’, or more affectionately, as ‘Northern Blues’. That name caused confusion though, since the ‘official’ Northern Bluefin is the northern Pacific Bluefin Tuna, Thunnus orientalis, a close relative of the Atlantic Giant Bluefin and the Southern bluefin. Therefore, to avoid confusion, the Aussie Northern (true) Blue has been officially dubbed the Longtail Tuna.

The most commonly cited feature that distinguishes the Longtail Tuna from other species is its elongated rear third of the body, extending from the second dorsal and anal fins. This ‘stretched’ body shape is fairly obvious even to the casual observer, but just to confuse the issue, it is not even true for small juveniles less than, say 3kg. Consequently, misidentification can sometimes be a problem with the longtail, especially for small fish. The species with which it is most commonly confused is the Yellowfin Tuna, but the longtail lacks the many pale stripes and rows of dots on the belly and flanks that live Yellowfin always show.

All of the line-class IGFA world records for Longtail have been taken off the Australian east coast between Moreton Bay in southern Queensland and the Victorian/ New South Wales border. The odd thing though is that such large fish (25kg plus) are rarely recorded in commercial catches anywhere

else in the world. On the other hand, because Longtail are found through most of southeast Asia and the coastal regions of the northern Indian ocean, extending into the Persian Gulf and the Red Sea, it is quite possible that other areas holding large adult fish are yet to be discovered, at least by sportfish anglers.

The all tackle world record Longtail was caught at Montague Island southern NSW in 1982 well known angler Tim Simpson. Around the same time, Tim and others caught other Longtail in excess of 30 kg at the same location, so it appears that this was a good example of the largest specimens of a species occurring at the very extremes of their geographical ranges. Some very recent ground breaking research published by CSIRO scientist and keen angler, Dr Shane Griffiths, found that longtail tuna spawn when they are just 55 to 60 cm long, at which size they are just 2 to 3 years old, and also found that there are three distinct Australian spawning areas – one along the Coburg Peninsular, NT, one in the eastern Gulf of Carpentaria and one extending from south of Cairns to the central Queensland coast. The latter spawning ground is the most likely source of the occasional ‘run’ of very small juvenile Longtails (1-2 kg) that appear off Fraser Island or as far south as Caloundra in summer.

Longtail Tuna tend to feed on small dietary items, even when adult. Anchovies and sprats, for example, are favored prey in Moreton Bay. Specialist anglers are aware of this, and use small baitfish such as Hardyheads, or very small lures or saltwater flies when targeting them. I once examined the stomach contents of a 5 kg Longtail caught off Hamilton Island that contained a fascinating variety of food items – all measuring about the same size (1.5 cm long) including Trigger Fish, Toadfish, Ponyfish, Squid and even a tiny Octopus.

Interestingly, a CSIRO study on the diet of longtail in the Gulf of Carpentaria also by Shane Griffiths found that they were generally very opportunistic feeders. He identified

101 different types of food items in nearly 500 stomachs, dominated by small Herrings and Anchovies. Other important items included Slimy Mackerel, Longtom, Garfish, Whiting, Squid and Prawns. Shane and his co-researchers even made some calculations on the total amount of food that the population of longtail in the Gulf might consume, and came up with a figure of 148,000 tonnes! One surprising finding was that of this total, about 550 tonnes consisted of commercially important Prawns, or about 11% of the entire catch of the northern Prawn fishery in the Gulf. Sounds like a good reason to try a Prawn pattern for that next Longtail trip.

Unlike other tropical Tunas, the Longtail rarely, if ever forms large schools. When small, they often associate with pods of Mackerel Tuna, and at times, will also aggregate with Dolphins and even Whale Sharks. Small schools of Longtail tend to surface only for brief periods, and are generally very flighty, being easily scared into sounding or scattering. An interesting observation uncovered in researching this article is that packs of 15 to 20 adult Longtail often attack their prey in an arrow shaped formation, each fish spaced equidistant from its neighbors. This form of cooperative feeding behavior has also been observed in Giant Atlantic Bluefin Tuna and Yellowtail Kingfish in southern California.

Not many anglers would realise that in 2007, the Longtail Tuna was declared a recreational-only species for all of Australia, a status that is very special, especially given the fact that worldwide catches of the species have skyrocketed to over 200,000 tonnes per annum in recent years. There is still a lot we don’t know about this enigmatic, coastal Tuna, but hopefully, its future in Australia as a top-rated angling species is looking good.