Researchers detect around 60 million nests of Antarctic icefish over a 240
square kilometres area in the Weddell Sea
Near the Filchner Ice Shelf in the south of the Antarctic Weddell Sea, a
research team has found the world's largest fish breeding area known to
date. A towed camera system photographed and filmed thousands of nests of
icefish of the species Neopagetopsis ionah on the seabed. The density of the
nests and the size of the entire breeding area suggest a total number of
about 60 million icefish breeding at the time of observation. These findings
provide support for the establishment of a Marine Protected Area in the
Atlantic sector of the Southern Ocean. A team led by Autun Purser from the
Alfred Wegener Institute publish their results in the current issue of the
scientific journal Current Biology.
The joy was great when, in February 2021, researchers viewed numerous fish
nests on the monitors aboard the German research vessel Polarstern, which
their towed camera system transmitted live to the vessel from the seabed, 535
to 420 metres below the ship, from the seafloor of the Antarctic Weddell Sea.
The longer the mission lasted, the more the excitement grew, finally ending in
disbelief: nest followed nest, with later precise evaluation showing that
there were on average one breeding site per three square metres, with the team
even finding a maximum of one to two active nests per square metre.
The mapping of the area suggests a total extent of 240 square kilometres,
which is roughly the size of the island of Malta. Extrapolated to this area
size, the total number of fish nests was estimated to be about 60 million.
"The idea that such a huge breeding area of icefish in the Weddell Sea was
previously undiscovered is totally fascinating," says Autun Purser, deep-sea
biologist at the Alfred Wegener Institute, Helmholtz Centre for Polar and
Marine Research (AWI) and lead author of the current publication. After all,
the Alfred Wegener Institute has been exploring the area with its icebreaker
Polarstern since the early 1980s. So far, only individual Neopagetopsis ionah
or small clusters of nests have been detected here.
The unique observations are made with a so-called OFOBS, the Ocean Floor
Observation and Bathymetry System. It is a camera sledge built to survey the
seafloor of extreme environments, like ice-covered seas. It is towed on a
special fibre-optic and power cable normally at a speed of about one half to
one knot, about one and half metres above the seafloor. "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," Autun Purser reports. "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," says the AWI expert.
Based on the images, the team was able to clearly identify the round fish
nests, about 15 centimetres deep and 75 centimetres in diameter, which were
made distinct from the otherwise muddy seabed by a round central area of
small stones. Several types of fish nests were distinguished: “Active”
nests, containing between 1,500 and 2,500 eggs and guarded in three-quarters
of the cases by an adult icefish of the species Neopagetopsis ionah, or
nests which 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 mapped the distribution and density of the nests using
OFOBS's longer-range but lower-resolution side scan sonars, which recorded
over 100,000 nests.
The scientists combined their results with oceanographic and biological
data. The result: the breeding area corresponds spatially with the inflow of
warmer deep water from the Weddell Sea onto the higher shelf. With the help
of transmitter equipped seals, the multidisciplinary team was also able to
prove that the region is also a popular destination for Weddell seals. 90
per cent of the seals’ diving activities took place within the region of
active fish nests, where they presumably go in search of food. No wonder,
the researchers calculate the biomass of the ice fish colony there at 60
thousand tonnes.
With its biomass, this huge breeding area is an extremely important
ecosystem for the Weddell Sea and, according to current research, likely to
be the most spatially extensive contiguous fish breeding colony discovered
worldwide to date, the experts report in the publication in Current Biology.
German Federal Research Minister Bettina Stark-Watzinger said: “My
congratulations to the researchers involved on their fascinating discovery.
After the MOSAiC expedition, German marine and polar research has once more
reaffirmed its outstanding position. German research vessels are floating
environmental research laboratories. They continue to sail the polar seas
and our oceans almost non-stop, serving as platforms for science aimed at
generating important findings to support climate and environmental
protection. Funding by the Federal Ministry of Education and Research (BMBF)
provides German marine and polar research with one of the most
state-of-the-art research vessel fleets worldwide. This discovery can make
an important contribution towards protecting the Antarctic environment. The
BMBF will continue to work towards this goal under the umbrella of the
United Nations Decade of Ocean Science for Sustainable Development that runs
until 2030.”
For AWI Director and deep-sea biologist Prof. Antje Boetius, the current
study is a sign of how urgent it is to establish marine protected areas in
Antarctica. "This great discovery was enabled by a specific under-ice survey
technology we developed during my ERC Grant. It shows how important it is to
be able to investigate unknown ecosystems before we disturb them.
Considering how little known the Antarctic Weddell Sea is, this underlines
all the more the need of international efforts to establish a Marine
Protected Area (MPA),” Antje Boetius classifies the results of the study, in
which she was not directly involved. A proposal for such an MPA has been
prepared under the lead of the Alfred Wegener Institute and is defended
since 2016 by the European Union and its member states as well as other
supporting countries in the international Commission for the Conservation of
Antarctic Marine Living Resources (CCAMLR).
Antje Boetius adds: “Unfortunately, the Weddell Sea MPA has still not yet
been adopted unanimously by CCAMLR. But now that the location of this
extraordinary breeding colony is known, Germany and other CCAMLR members
should ensure that no fishing and only non-invasive research takes place
there in future. So far, the remoteness and difficult sea ice conditions of
this southernmost area of the Weddell Sea have protected the area, but with
the increasing pressures on the ocean and polar regions, we should be much
more ambitious with marine conservation.”
Reference:
Autun Purser, Laura Hehemann, Lilian Boehringer, Sandra Tippenhauer, Mia Wege,
Horst Bornemann, Santiago E. A. Pineda-Metz, Clara M. Flintrop, Florian Koch,
Hartmut H. Hellmer, Patricia Burkhardt-Holm, Markus Janout, Ellen Werner,
Barbara Glemser, Jenna Balaguer, Andreas Rogge, Moritz Holtappels, Frank
Wenzhoefer: Icefish Metropole: Vast breeding colony discovered in the southern
Weddell Sea, Current Biology (2022).
DOI: 10.1016/j.cub.2021.12.022
What is an Ice Fish??? This is a very long winded article without saying much at all about the species of the fish, but only everything about that they have been found. Tell us more about the fish.
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