The humpbacks swim in corkscrew patterns toward the water’s surface near the fish. As the whales swim in ever-smaller revolutions, they discharge bursts of air through their blowholes. One burst of bubbles, forming a bubble cloud, discharges every second during this process.
The result is a bubble net that may be close to 100 feet wide. Similar to a fisherman’s net, the bubbles enclose the herring, preventing escape. Whales capture schools the size of a house containing close to a million fish in this manner.
Diachok and his colleagues believe whales may even classify fish before they catch them. The scientists observed pairs of humpback hunting teams. One whale would swim beneath a school and herd fish towards the surface. A second whale on top of the school then emitted tonal sounds.
The researchers believe the sounds transmit across schools and can resonate through the fishes' air-filled bladders. An acoustic “shadow” results, similar to how doctors use x-rays to see inside bodies.
Diachok explained, “If one humpback transmits a series of tones, like plucking all the strings of a harp, then the listening (bottom) whale may notice that he can hear all of the tones, except for the one, which corresponds to the resonance frequency of fish swim bladders when the school of fish is swimming between the transmitting and listening whale.”
The researchers believe the listening whale detects the missing frequency and may use this information to discriminate between fish species and perhaps to even estimate the size and weight of the fish.
