New Study: Herring use farting to escape from whales

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Norwegian killer whales slap their tails underwater to disorient and kill herring, which sometimes defend themselves from the assault by disappearing under the cover of their own bubbly flatulence, according to a new study.

The study is one of two papers presented at the recent Acoustical Society of America Meeting in Rhode Island that addressed some of the clever techniques whales employ to catch their dinner.

While whales often are successful, some herring escape. The study's authors perhaps say it best: "Farting may save their lives."

"The (herring) bubbles are released through the anal duct when the air expands as the fish ascend," explained Malene Simon, who worked on the research. "We do not know if the fish release air when staying at one depth as a reaction when meeting a predator. However, it is very likely that the bubble will confuse or scare the predator in such a way that the herring will have a better chance of escaping."

Simon, a researcher at the Greenland Institute of Natural Resources, added, "This effect would probably be much less significant for one lonely fish than when it is a large school of fish. The air bubbles reflect sound and make it difficult (for the whales) to locate the fish with echolocation."

Undaunted by flatulent fish, killer whales dive - often several hundred feet - to drive herring up to shallower waters, Simon told Discovery News. As they dive, they emit a cacophony of clicks and whistles that seem to scare and tighten the fish schools.

The whales also slap their tails underwater in a way that can kill or disorient stunned fish, which the whales then leisurely munch one by one.

Simon said Icelandic killer whales have refined this technique. They herd and tail slap like their Norwegian relatives, but also emit an intense siren-like sound that appears to force terrified fish into an even tighter ball.

Orest Diachok, a research physicist at Johns Hopkins University, told Discovery News that the killer whale study provides "compelling evidence on the function of tail slaps, much more compelling than previous studies of this phenomenon."

As for the herring flatulence, Diachok agreed the fish may do this to facilitate escape, but he said it also might just be inadvertent.

Diachok and his team discovered that whales use similar bubbles to their own advantage. They studied humpback whales in the Gulf of Alaska.

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.
By Jennifer Viegas, Discovery News