Giant Bluefin Tuna Invade Australian Watersff

They’re taller than the average footballer, weigh as much as a fridge and have hundreds of anglers clamoring to catch them. Schools of giant southern bluefin tuna have invaded the waters off the South-East Australia.

Their sudden appearance over the past fortnight has baffled scientists and the anglers who have converged on the area from as far away as Sydney to chase the prized sportfish.

One hypothesis is a unique combination of a cold water upwelling from the deep ocean off the continental shelf and an unusually warm inshore surface current off the south-eastern coast.

The rare event could have brought the monster tuna closer to shore, up to 100km inside their normal migratory track well off the continental shelf.

The giant fish - some more than 2m long and weighing 150kg - have appeared in large schools between Port MacDonnell and Portland, in western Victoria.

The phenomenon has provided a once-in-a-lifetime opportunity for hundreds of anglers, who have descended on both Port MacDonnell and Portland in the hope of catching one of the behemoths.

CSIRO deputy chief of marine and atmospheric research Dr John Gunn said there was “no simple explanation” for the sudden appearance of the big tuna. “We know these animals migrate through the Great Australian Bight along the continental shelf past the western corner of Victoria at around this time each year,” he said. “For some reason, they are closer to shore this year, but we don't know exactly what the motivation is.” He said the nutrient-rich cold water in the upwelling was a magnet for huge numbers of baitfish, which fed on the plankton and other organisms brought to the surface from the ocean floor. CSIRO satellite photographs have revealed water temperatures off the continental shelf as low as 14 degrees in some areas.

But just 50km inshore, fishermen have reported water temperatures as high as 20.4 degrees - complete with leatherback turtles - a species normally found in the tropics. “My hypothesis at the moment is the tuna are keying in on what is likely to be a surface abundance of small fish and squid that are driven to the surface by this cold water,” Dr. Gunn said. ”The fish are obviously coming off that and moving into the warmer water inshore. My guess is they have found themselves a patch of productive water and it has kept them resident for longer than usual”.

Geelong angler Rob Zynevych, 47, has so far caught the biggest tuna - a massive 120.7kg fish - in the bonanza. He was fishing with mate Sam Muscat 60km south-west of Portland on March 30 when the pair caught four fish weighing 78kg, 80kg, 108kg and the 120.7kg monster. ”I knew it was big and when I first saw it the thing made the others look small,” he said. “I have seen some big fish before, but this just blew me away.” Mr. Zynevych said the largest fish took him 40 minutes to land using a 37kg line on a specialist game rod and reel.

Portland angler Brett Wakeley caught a 90kg tuna off Port MacDonnell a fortnight ago when the fish arrived. He has since landed off Portland a bigger fish - 109.5kg - which took him an hour and 40 minutes to catch. “Mate, it was one of the toughest fish I've ever caught,” he said. “Mine was huge, but there are blokes who have lost even larger fish after fighting them for up to eight hours.”

Mr. Wakeley said he believed abnormally high water temperatures in the area may be responsible for the influx of large fish. His fish were caught in water that was in the 18 to 19 degrees range, compared with the normal temperature of 16.5 to 17 degrees.

”An abundance of small slimey mackerel the tuna are feeding on in the same area may also be another factor,” he said. “The tuna are absolutely full of them”. Portland angler and photographer Bob McPherson said experienced local anglers had never witnessed anything close to the past fortnight’s activities. “Everyone is astounded by what has been happening. Every year a few big fish are caught, but nothing like this has ever taken place,” he said.

While the largest fish landed so far has topped the scales at 120.7kg, there have been many reports of bigger fish sighted and lost. One angler hooked a fish estimated at 150kg but lost it when the hooks pulled out of its mouth at the side of the boat after eight hours.

Mt Gambier fishing tackle store owner Craig Philp said the event had boosted business. So many anglers had bought big game fishing reels and heavy rods from his Spot On tackle store that supplies had been exhausted for some brands within Australia.

”We have done a year's worth of business in a fortnight,” he said. “It’s been phenomenal. Lures and heavy line and trace material have been snapped up by those wanting to get in on the action.”

Even tackle shops in Adelaide have been joining in the bonanza as local anglers stock up prior to heading south. Fisherman’s Paradise owner Keith Goodie said yesterday his Pirie St shop had been inundated over the past fortnight.

”I have sold out of the big skirted lures they're using to catch these fish,” he said. “Blokes are buying six to eight at a time and I've had to order more in.”