On a very cold morning at 3 a.m., a student researcher by the name of Lilian Boehringer was sailing on a boat across the Weddell Sea, just off the Antarctic Peninsula. It was already full-light, but most of her crew mates were sleeping in their beds.

Out of the gloom on her remotely operated camera, which was surveying the seafloor more than 1,000 feet below the boat, she saw a shape come into view – a small dimple in the seafloor about 3 feet across. Then there was another and another, and soon they filled the camera. Each dimple held an icefish, a long, thin fish with bat-like fins that are very similar in shape to many of the catfish commonly kept in home aquariums. Boehringer knew that almost all the fish were protecting a clutch of eggs.

Half an hour later, Autun Purser (a deep-sea biologist) joined Boehringer, and still nest after nest filled the camera’s view. They were surprised to see such a density of icefish when there was no record of them being there – why hadn’t anyone seen them before?

The nests continued for a breathtaking 4 hours, with 16,160 icefish being caught on camera. They followed this first remote camera dive with another two, which allowed them to estimate the icefish colony covered 92 square miles, with over 60 million nests, with each nest containing up to 1,753 eggs. Not only was this a breathtaking discovery considering the location, but it is also now considered the largest active fish breeding colony ever discovered.

The icefish guard their nests against predators that would find these large, nutritious eggs an easy meal. Typical predators do not include other fish or even the parent fish (as so many other fish species often do), but sea spiders (yes, they look like their name!), starfish, and polychaete worms, which look like an underwater centipede.

While the average temperature in the Weddell Sea ranges from -0.8C to 0C (31.8F – 32F), the colony is in an unusually warm area of the sea. The area the colony inhabits averages 1.7C (35F), a small change to us but a big one when you consider the average temperature is below freezing.

The Weddell Sea is not as barren as you may imagine, despite the freezing temperatures. The large settlement is, perhaps unsurprisingly, a favorite dining location for local seals. These seals can dive up to 2,000 feet and hold their breath for up to 45 minutes at a time, which gives them ample time to prey upon the adult icefish in and around the nests 1,000 feet down.

The team deployed a camera that will stay in the area and take pictures of the colony twice a day for two years so they can learn more about how these fish are living and hopefully get some of their many questions answered. They hope to find out how the fish find a mate, how they prepare their nests, and what part they play in the bigger Weddell Sea food chain.