"Largest-ever" fish breeding colony may contain up to 60 million nests
German scientists have announced the discovery of what is claimed to be the world's largest fish breeding area known to date. Described as a globally unique ecosystem, it consists of tens of millions of icefish nests on the Antarctic sea floor.
The nesting area was first observed last February, when researchers from the Alfred Wegener Institute were exploring the Filchner Ice Shelf in the southern Weddell Sea. They were aboard the icebreaker RV Polarstern.
Travelling at 1 to 4 km/h (0.6 to 2.5 mph), that vessel was towing an uncrewed 1-ton (0.9-tonne) submersible known as the Ocean Floor Observation and Bathymetry System (OFOBS). The latter stayed about 1.5 to 2 meters (4.9 to 6.6 ft) above the seafloor – at a depth of 420 to 535 m (1,378 to 1,755 ft) – recording video footage, taking photographs and gathering bathymetry data.
Upon viewing the images, the scientists were amazed to discover a huge breeding colony of nesting notothenioid icefish (Neopagetopsis ionah). Although only "a few dozen nests" had previously been spotted together in the Antarctic, the new colony is estimated to include about 60 million active nests, and to cover an area of at least 240 sq km (93 sq mi). These figures are extrapolated from the mapping of a 45,600-sq-m (490,834 sq-ft) area, in which 16,160 nests were spotted.
Consisting of a circle of small stones on the muddy seabed, each nest measures about 15 cm deep by 75 cm wide (5.9 by 29.5 in). The majority of them contain at least 1,700 eggs, which are guarded by a single adult fish.
It is believed that the presence of such a large colony may be at least partly due to a localized upwelling effect, which causes the seabed waters in the surveyed area to be about 2 ºC (3.6 ºF) warmer than is normal for the region. The Weddell seals in the area certainly seem to appreciate the nearby food source – by attaching transmitters to some of the seals, it was found that about 90 percent of their diving activity takes place in the nesting area, at the depths where the nests are located.
Two camera systems have been left in place to observe the colony until a research vessel is able to return to the site, which should be sometime in April. It is hoped that the team's findings will support the establishment of a Marine Protected Area.
"The idea that such a huge breeding area of icefish in the Weddell Sea was previously undiscovered is totally fascinating," said the lead scientist, deep-sea ecologist Autun Purser. A paper on the study was recently published in the journal Current Biology.