Deep-sea biologists surveying the Weddell Sea in Antarctica, to observe the impact of climate change on local ecosystems, came across an icefish nesting site that is roughly the size of the island of Malta, making it the world's largest fish breeding area found so far, according to a press release.
Icefish are not only known for their ghostly appearance and the region they inhabit below the Antarctic ice, they are also the only known vertebral animals that do not have hemoglobin in their bodies as adults. Hemoglobin carries oxygen to various cells in the body as an important component of blood. However, with high oxygen levels in Antarctic waters, these fish can work with very low levels of hemoglobin in their bodies.
The discovery was made by researchers at the Alfred Wegener Helmholtz Centre for Polar and Marine Research who were surveying the region with their towed camera system, aboard the German research vessel, Polarstern. The system called the Ocean Floor Observation and Bathymetry System or OFOBS, consists of a camera mounted on a sledge and towed by special power and fiber optic cables at speeds no faster than one knot.
During a routine survey in February last year, the researchers chanced upon numerous icefish nests that were transmitted to the ship from a depth of up to 1,755 feet (535 m). Each nest is about two and a half feet wide (75 cm) and half a foot (15 cm) deep and is clearly marked with a circular arrangement of small stones. Each nest contains up to 2,500 eggs and is guarded by an adult fish.
Polarstern has been actively involved in surveys since the 1980s and icefish have only been found in small clusters until this discovery. So when researchers onboard the vessel found the nesting sites, they wanted to explore the expanse of the site. They decreased the resolution of the camera and increased the speed of the vessel to up to three knots. They surveyed an area of roughly 500,000 sq feet (45,000 sq m) and found over 16,000 fish nests. The area extends up to 92 square miles (240 sq km) so by extrapolation, the nesting area contains about 60 million fish.
The huge breeding area is massive biomass and an important ecosystem in the Weddell Sea, the researchers reported their findings in the publication Current Biology and have called for international efforts to designate it as a marine protected area.