Tuna, mulloway and kingfish

Tuna, mulloway and kingfish

Justin North
5 recipes
Published by
Hardie Grant Books
Steve Brown

The Stehr Group

Port Lincoln is the gateway to the Great Australian Bight and a fishing hub servicing markets such as Asia and the USA. It is home to the most diverse commercial fishing operations in Australia, with established tuna, prawn, lobster, sardine, crab, abalone, oyster, mussel and scallop businesses. Generous fishing quotas are in place to encourage industry, but are also regulated to discourage overfishing. Aquaculture employs between 15 and 20 per cent of Port Lincoln’s population, with another 15 to 20 per cent working in related industries.

The Stehr Group founder Hagen Stehr emigrated to Australia from Germany as a boy. He started out with an abalone boat, which he traded for a prawn trawler after a while. Hagen Stehr started his business with long-line fishing and ‘poling’ (hauling the fish from the water by hand while standing on a platform) and his tuna fishing methods developed. He founded the Stehr Group of companies in 1969. ‘Initially we were just wild-catch fishermen,’ Marcus Stehr, Hagen’s son, explains. There are still only five tuna fishing enterprises in the Port Lincoln area and Stehr is keen for the industry to grow.

Over the years, Hagen Stehr has forged a strong identity in the fishing industry. He is chairman of the Australian Fishing Association and is a well-known member of the fishing community in the Port Lincoln area and beyond. In 1997 he was awarded the Order of Australia medal; Stehr has been credited with elevating fishing to an artisan level.

The aquaculture arm of the Stehr Group has expanded from focusing on yellowtail kingfish initially to mulloway (also known as suzuki or jewfish) and southern bluefin tuna. Much research and development has gone into the propagation of southern bluefin tuna, and the Stehr Group is in the process of building an onshore facility to continue this project. Closing the breeding cycle (being able to grow tuna from initial spawn through to harvested adult, all in captivity) could eliminate much of the cost of searching for and catching young tuna in the Great Australian Bight.

Southern bluefin tuna ranching

Flying into Port Lincoln across the Spencer Gulf, round fish pens can be seen from the air, flowing in threads from the harbour to open water. The Stehr Group operates over a dozen pens during the winter season and more in the summer. Each tuna pen spans 40 or 50 metres in diameter and can be as deep as 15 metres. Insuring the fish in these pens alone costs around A$250,000 annually, which is perhaps an indication of the value of the tuna fishing industry in Australia.

Rearing tuna is a far more complicated process than raising any other fish from a hatchery. Because tuna are very sensitive to their environment, and spawn only in deep water, the conditions under which they might spawn in captivity have not yet been perfected in Australia. Hagen Stehr actively promotes research in this area through spawning programs, with assistance from the government.

Spotter planes fly over the expanse of the Bight between December and March on the lookout for the discolouration in the water, which marks the presence of a large school of young tuna. It is while these tuna are migrating that they are captured, using a method called ‘purse seining’. The planes direct boats, loaded with hauls of live pilchards in their holds, towards the tuna. The pilchard bait is released and a large net encircles the school and traps as many fish as possible – in the thousands.

Beneath the water, the tuna are transferred to a pen which is then towed at a speed of one knot all the way back to the outer reaches of Port Lincoln, where the tuna are positioned to grow in water rich in oxygen thanks to strong currents circulating. Here the fish are fed Australian pilchards and imported fatty fish until they’ve grown sufficiently to sell on the open market. The process of fattening tuna for market takes about four months.

Preparing the tuna for market is a unique practice. Early in the morning, a diving team of four enters the pen and encircles the fish with a net that lies below them. As the sun rises, the net is tightened and raised toward the surface, making the area of water shallow enough for divers to chase each fish individually. They slide a hand into its gills (which appears to pacify the giant fish) and lead it to the edge of the boat.

The Japanese method of killing tuna is used in Australia. It is known as iki jime. A corer is pushed into the brain of the fish and a slim wire rod is slid in and along the fish’s spinal column, disconnecting the nerves from the spinal cord and preventing rigor mortis, which can adversely affect the flavour of the fish. The gills are removed, the fish is weighed and within a couple of minutes, the tuna is bathed in salted ice for its journey to the factory. This keeps the flesh fresh without freezing it, so it will taste its best hours or days later.

There is at least one tuna expert on board the fishing vessels at all time, judging the quality of the fish for prospective buyers. This person is in constant contact with the markets, informing them on the quality of the fish coming out of the southern seas.

Being a member of a tuna dive team is not without its dangers; great white sharks, breeding at the nearby and aptly named Dangerous Reef, are frequent visitors to the pens, to try and feed on the fattening tuna. They have been known to tear through the netting and eat the trapped fish, before becoming trapped in the net themselves. Divers are faced with the unenviable reality of not knowing what else is in the pen with them when they enter the cold water before sunrise. The work is physically taxing; there have even been cases of tuna having broken human arms with a flick of their tail.

The next port of call

Once back on dry land, the tuna are taken to a processing plant not far from the water’s edge. Here they are gutted, thoroughly cleaned, weighed, measured, and evaluated. A sliver of meat is cut from the base of each fish’s tail and closely inspected. The Japanese market (which is where a large portion of the Stehr Group’s tuna ends up) favours a fatty meat of a deep red hue. From the cut at the base of the tail, the fat beneath the skin, as well as the intramuscular fat, can be clearly evaluated. Australian-reared tuna is more fatty than the fish grown and harvested in Japan, making the product a desirable one for the Japanese sashimi market.

The most expensive part of the tuna flesh is the belly (toro in Japanese), which has the most concentrated marbling of fat. On the current market this part of the fish will earn A$250 a kilogram.

Tuna must never be frozen if it is to retain its premium asking price, so the fish have capsules of an innocuous gel ice placed in their bellies and around their bodies. It is in this form that the fish are shipped around the country and overseas. Pallets of tuna leave Port Lincoln by road to Adelaide or by air straight from the local airport, a few minutes out of town.

As each fish has been weighed and examined, it can be ‘identified’ and traced from this point all the way to its final destination in the markets or individual kitchens.

Clean sea hatchery

The Stehr Group’s hatchery operates at Arno Bay, a sparsely populated town 115 kilometres north of Port Lincoln. In warehouses also containing state-of-the-art laboratories, mulloway and yellowtail kingfish are reared from larvae to young fish, and continue their development in pens of filtered ocean water similar to the ones that will house them later in the open water.

Morten Deichmann completed his biology degree in his native Denmark before embarking on a career path that has taken him around the world. Deichmann worked on Cyprus, in Italy, Bangkok and regional Thailand before arriving in Australia in 2003. He now engineers the management of all the fish at the hatchery – from spawning right through to their departure for the sea pens.

Through artifical light and controlled water temperatures the fish are encouraged to think it’s the spawning season, and they spawn for longer. Fertilised eggs are then collected from the spawning tanks and placed in incubation tanks, where they hatch into larvae four or five millimetres in length. These larvae are fed rotifers – tiny zooplankton which themselves feed on cultivated algae grown at the hatchery by a marine biologist. Plastic vats at the hatchery hold thousands of litres of the algae, which bubble a brilliant green.

The larvae progress to artemia – commonly known as brine shrimp or sea monkeys. These shrimp grow to between 10 and 15 millimetres in length and are also cultivated at the hatchery. After a month of feeding, the larvae are weaned onto a more solid diet of fish meal pellets, which speed their growth, for a further month. At this stage, the fish weigh about five grams, are about 10 centimetres long, and are ready to be transferred to sea pens to reach maturity. This is a process of at least two years as the fish grow in their ocean homes. The water locations are selected for their rich oxygen content and clear currents.

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