Typically used on slow-moving research vessels, the sonar cannot capture the ever-changing motion of shoals. Instead, scientists must fill in the gaps of fish group behavior using theoretical, statistical and other models.
Makris and his team developed a system using low-frequency sonar, which propagates tens of kilometers in all directions the way ripples on the surface of a pond move away from a dropped pebble.
When the waves come into contact with an object or a group of fish, they bounce back and are collected by an antenna being towed behind the ship.
"What it's enabling people to do for the first time is to see instantaneously a 30-kilometer radius in 360 degrees," said Makris.
In experiments in waters south of Long Island, New York, the scientists saw some interesting traits in the fish populations.
For example, the fish often congregate in an hourglass pattern, a thin bridge connecting the two ends. The shape has been observed before in small schools, but this is the first time it was observed in such an enormous group.
They also noticed that the shoal was sharply bounded on one side to the edge of the continental shelf, where nutrients well up from deeper water. Makris thinks following the edge of the shelf could possibly be a form of navigation for the animals.
The one thing the technology can't do yet is determine the species of fish. And this could prove difficult if the vessel is imaging the shoal from tens of kilometers away, said Pitcher.
But according to Makris, the technique could be used in combination with other methods that determine fish species or could be used to track known shoals.
