Massive icefish breeding colony is found in Antarctica's Weddell Sea

World’s largest fish breeding colony that’s the size of BIRMINGHAM and includes 60 million active nests is found in Antarctica’s Weddell Sea

  • The unprecedented fish population is a biomass of more than 135 million pounds
  • Most of the nests were occupied by a single adult guarding over 1,700 eggs 
  • Scientists believe the area is utilised heavily by seals and other predators
  • The icefish, or notothenioids, play an important role in the wider food web  

A massive icefish breeding colony, covering almost 100 square miles, has been discovered in Antarctica’s Weddell Sea, with about 60 million active nests.

It is the world’s largest breeding colony of fish, representing a biomass of more than 135 million pounds, and covers an area roughly the size of Birmingham.

Until now it was not known that such a thing existed. 

Each of the nests include about 1,700 eggs, with a number of fish carcasses found within, or near the site – as it is thought to be a feeding ground for seals.

Also known as notothenioids, these fish play an important role in the wider food web, say experts from the Alfred Wegener Institute in Bremerhaven, Germany. 

The discovery will play an important role in the conservation of Antarctica and surrounding oceans, the researchers claim, adding that they plan to return to the area later this year to survey more of the ocean floor for signs of nests. 

A massive icefish breeding colony, covering almost 100 square miles, has been discovered in Antarctica’s Weddell Sea, with about 60 million active nests

Each of the nests include about 1,700 eggs, with a number of fish carcasses found within, or near the site – as it is thought to be a feeding ground for seals

WHAT ARE ICEFISH (NOTOTHENIIDAE)? 

Nototheniidae, the notothens or cod icefishes, live in the Southern Ocean.

They are a family of ray-finned fish first described in 1861, with the name meaning ‘coming from the south’. 

They are found around the Antarctic and have elongated bodies. 

They typically have two dorsal fins and grow to up to 85 inches.

Researchers from Germany discovered more than 60 million icefish nests in the Southern Ocean near Antarctica. 

The team used an underwater camera ‘sledge’ called Ocean Floor Observation and Bathymetry System (OFOBS) in the southern Weddell Sea, Antarctica.

The researchers were surveying the Filchner ice shelf, a vast slab that has floated off the land onto the sea, as well as the surrounding seafloor, which included an upwelling of water that was 3.6 F warmer than the surrounding area.

While they were able to examine the change in water temperature, finding the massive fish colony and breeding ground was ‘rather unexpected’.     

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.

Lead author Dr Autun Purser said data revealed this area is a prime feeding ground for seals, with ‘a great many spending their time in close proximity to the 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.’

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

The researchers used an underwater camera ‘sledge’, OFOBS, which is a large, towed device, weighing one ton and towed behind the icebreaker RV Polarstern.

‘We tow this at a height of about 5ft to 8ft above the seafloor, recording videos and acoustic bathymetry data,’ explained Dr Purser. 

Live images were transmitted from 1,755ft to 1,377ft down to monitors aboard the research ship, and the longer the mission lasted, the more excitement grew.

The discovery will play an important role in the conservation of Antarctica and surrounding oceans, the researchers claim, adding that they plan to return to the area later this year to survey more of the ocean floor for signs of nests

The team used an underwater camera ‘sledge’ called Ocean Floor Observation and Bathymetry System (OFOBS) in the southern Weddell Sea, Antarctica

‘Oasis of life’ is discovered beneath Antarctica’s Ekström Ice Shelf 

Deep beneath the Antarctic ice shelves, the environment is about as harsh as it gets.

Extremely cold, perpetually dark and with food sources almost non-existent, it is not exactly conducive to life, even if Earth is home to some remarkably hardy and resolute creatures that exist in all corners of the world.

But surprisingly scientists have discovered 77 species living there, including evidence that this ‘oasis of life’ dates back some 6,000 years.

Among them were sabre-shaped moss animals and unusual worms, researchers in Germany found.

Using hot water, the team from the Alfred Wegener Institute (AWI) drilled two holes through nearly 656ft (200 metres) of the Ekström Ice Shelf near Neumayer Station III in the South Eastern Weddell Sea in 2018.

Nest followed nest, the team said. Precise evaluations identified an average one breeding site per 33 square foot – with up to two per 10 square feet.

Mapping suggested it extended across a region roughly equivalent to an island the size of Malta – about 92 square miles.

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. 

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 [490,000 sq ft] and counted an incredible 16,160 fish nests on the photo and video footage.’

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 per cent of diving activities occurred there.

Nest followed nest, the team said. Precise evaluations identified an average one breeding site per 33 square foot – with up to two per 10 square feet

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

Bettina Stark-Watzinger, German Federal Research Minister, congratulated the researchers on their discovery, saying it makes an important contribution towards protecting the Antarctic environment.

The researchers have now deployed two camera systems to monitor the icefish nests until a research vessel returns. 

The hope is that photographs taken multiple times a day will yield new insights on the workings of this newly discovered ecosystem. 

Purser says he has plans to return in April 2022 for surveys of the seafloor in areas of the northeast Weddell Sea. 

The findings have been published in the journal Current Biology. 

ALL YOU NEED TO KNOW ABOUT WEDDELL SEALS 

Scientific name: Leptonychotes weddellii

Description: Weddell seals are large animals. Both adult males and females are about 3 metres long and weigh around 400–500kg. The head is small relative to body size and the colour is usually dappled grey and black on the back with a mostly white under-belly.

Distribution and abundance: Weddell seals have a circumpolar distribution and are coastal, staying around the fast ice and venturing only 9-12 miles (15–20km) into the Southern Ocean to feed. Weddell seals haul-out onto the fast-ice to rest and moult, and for females to pup.

Weddell seals are incredibly placid sedentary animals. They can be approached without much apparent stress to the animal. When they haul-out they remain close to their access hole on top of the ice. Underwater they remain relatively close to their breeding colonies, usually within 50–100km though occasional migrations of several hundred kilometres do occur, especially by juveniles.

Weddell seals are the most southerly ranging mammal to permanently inhabit the continent. Sightings of the seals have been made in New Zealand and Australia, though they are very rare here.

Threats: The under-ice environment is relatively safe from air breathing predators such as killer whales and leopard seals.

Special adaptations: Because Weddell seals breath air and live under the fast-ice, they must breath through cracks and holes in the ice cover. There are many cracks in the ice during the warmer summer months.

During winter these openings freeze over and Weddell seals use their canine and incisor teeth to rasp open the new ice and so maintain holes through which to breathe. 

Conservation status: least concern

Breeding: Weddell seals haul-out onto the stable fast-ice to rest and moult, and for females to pup, returning to the same area each year. Females of 6 years and over give birth in October to 1 pup per year. Pups weigh 25–30kg at birth and mothers care for them for 6 weeks by which time they have grown to 110–140kg. Pups learn to swim and haul-out of the water from 1 week old.

During the breeding season males defend underwater territories from other males for access to breathing holes and females. Both male and female seals vocalise, males may do so to maintain established territories. The only observation of mating (Cline et al, 1971) reported that it took place under water for 5 minutes or more. The male maintained rhythmic body undulations at a rate of 160 per minute.

Diet and feeding: Weddell seals are carnivores. Their food varies with time and location but mid-water (pelagic) and bottom dwelling (benthic) fish, squid, octopus and prawns are common. One seal was repeatedly observed to capture a fish weighing more than 40kg. Weddell seals are very capable divers, remaining under water for up to 45 minutes and reaching depths as great as 720m in search of prey. Lengthy shallow dives are probably exploration dives for new ice holes and food sources.

Source:  Australian Antarctic Program

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