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World’s largest fish breeding colony discovered in Antarctica

Nests of icefish discovered in Antarctica. (Credits: AWI OFOBS Team / SWNS)

The world’s largest breeding colony of fish has been discovered in Antarctica.

It covers at least 150 square miles – and includes about 60 million active icefish nests.

The unprecedented population represents a biomass of more than 60,000 tons – or over 135 million lbs.

Most were occupied by a single adult guarding more than 1,700 eggs. There were many fish carcasses within and near the site.

It suggests the notothenioids, or icefish, play an important role in the wider food web.

Its believed the colony is utilised heavily by seals and other predators.

Lead author Dr Autun Purser said: ‘A great many seals spend much of their time in close proximity to the fish nests.

‘We know this from historical tracking data and fresh tracking data from our cruise. The nests are exactly where the warmer water is upwelling.

‘These facts may be coincidence, and more work is needed, but the recorded seal data show seals do indeed dive to the depths of the fish nests, so may well be dining on these fish.’

The mysterious icefish colony is located in the southern Weddell Sea on the eastern side of the Peninsula.

Their bodily fluids contain antifreeze proteins that enable them to survive the very cold temperatures of the Southern Ocean.

As a result, blood is less thick and sticky – increasing supply of oxygen to organs.

Dr Purser, of the Alfred Wegener Institute, Bremerhaven, said: ‘Our most important finding is the pure existence of such an extensive icefish brooding colony.

‘A few dozen nests have been observed elsewhere in the Antarctic – but this find is orders of magnitude larger.’

Last February the German team surveyed the Filchner ice shelf – a vast slab that has floated off the land onto the sea.

They used an underwater camera ‘sledge’ called OFOBS (Ocean Floor Observation and Bathymetry System.

Explained Dr Purser: ‘Basically this is a large, towed device, weighing one ton, which we tow behind the icebreaker RV Polarstern at a speed of one to four kilometres per hour.

‘We tow this at a height of about 1.5 to 2.5 metres above the seafloor, recording videos and acoustic bathymetry data.’

The RV Polarstern in the Wendall Sea, Antarctica. (Credits: AWI – Tim Kavelage / SWNS)

It is pulled on a special fibre-optic and power cable normally at a speed of about one half to one knot.

Live images were transmitted from 535 to 420 metres down to monitors aboard the research ship.

The longer the mission lasted, the more the excitement grew – finally ending in disbelief.

Nest followed nest. Precise evaluations identified an average one breeding site per three square metres – with up to two per square metre.

Mapping suggested it extended across a region roughly equivalent to an island the size of Malta.

Dr Purser said: ‘The idea such a huge breeding area of icefish in the Weddell Sea was previously undiscovered is totally fascinating.’

The Polarstern icebreaker has been exploring it for four decades. Only individual Neopagetopsis ionah fish or small clusters of nests had ever been detected.

They knew the area included an upwelling 2C warmer than surrounding bottom waters. But the rest of what they found was a shock.

Dr Purser said: ‘We did not know to expect any sort of fish nest ecosystem.’ That part, he adds, came as a ‘total surprise.’

Dr Purser said: ‘After the spectacular discovery of the many fish nests, we thought about a strategy on board to find out how large the breeding area was – there was literally no end in sight.

‘The nests are three quarters of a metre in diameter – so they are much larger than the structures and creatures, some of which are only centimetres in size, that we normally detect with the OFOBS system.

‘So, we were able to increase the height above ground to about three metres and the towing speed to a maximum of three knots, thus multiplying the area investigated.

‘We covered an area of 45,600 square metres and counted an incredible 16,160 fish nests on the photo and video footage.’

The unprecedented population represents a biomass of more than 60,000 tons – or over 135 million lbs. (Credits: AWI OFOBS Team / SWNS)

The round fish nests could be clearly identified – about six inches deep and two-and-a-half feet in diameter.

They stood out from the otherwise muddy seabed due to a circular central area of small stones. Several types were distinguished.

Some were ‘active’ with between 1,500 and 2,500 eggs and guarded in three-quarters of cases by an adult icefish of the species Neopagetopsis ionah.

Others contained only eggs. There were also unused nests, in the vicinity of which either only a fish without eggs could be seen, or a dead fish.

The researchers used OFOBS’s longer-range but lower-resolution side scan sonars – which recorded over 100,000 nests – to work out distribution and density.

They were a popular destination for seals in search of food. Transmitters attached to the marine mammals showed 90 percent of diving activities occurred there.

It’s likely to be the most spatially extensive contiguous fish breeding colony discovered worldwide to date.

Bettina Stark-Watzinger, German Federal Research Minister, said: ‘My congratulations to the researchers involved on their fascinating discovery.

‘This discovery can make an important contribution towards protecting the Antarctic environment.’

The findings reported in the journal Current Biology reveal a globally unique ecosystem – backing calls for a regional Marine Protected Area in the Southern Ocean.

It would be under the Convention on the Conservation of Antarctic Marine Living Resources umbrella.

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