On the 3rd of October, 2006, Nicolas Makris watched a quarter of a billion fish gather in the same place. They were Atlantic herring, one of the most abundant fishes in the ocean and one prone to gathering in massive schools. This was the first time that anyone had watched the full scope of the event, much less capture it on video.
The first signs of the amassing herring appeared around 5pm and by sunset, the gathering had begun in earnest. Once a critical level of fish was reached, the shoal expanded at a breakneck pace, suddenly growing to cover tens of kilometres within the hour. By midnight, the shoal contained about 250,000,000 individuals – 50,000 tonnes of fish gathered in one place.
The ability of fish to congregate in gigantic schools may be familiar but until now, we’ve known remarkably little about the things that set off these gatherings. Without Facebook as a coordinator, what causes small groups of herring to take sociability to an extreme? Scientists have tried to follow gathering fish aboard research vessels but these can usually only see a small fraction of the massive schools are any one time.
Makris wasn’t so hampered. He used a new technique called Ocean Acoustic Waveguide Remote Sensing (OAWRS) that can visualise fish populations over vast distances in real-time. It needs two ships, one to send out sound waves in all directions and a second to pick up their echoes as they bounce off fish and floor alike.
In an instant, it can scan an area of ocean 100km in diameter, and it can update its images every 75 seconds, providing an unprecedented view of the genesis of herring shoals. The location was Georges Bank off the coast of Maine, where herring migrate to spawn in early autumn. Makris pointed his instruments at an area where herring historically gather, and waited.