Killer Whales and Herring: Using Sound to Get a Meal
Lee A. Miller (
lee@biology.sdu.dk
),
Malene Simon, Fernando Ugarte, and Magnus Walberg
Institute of Biology
University of Southern Denmark
Campusvej 55
5230 Odense M
Denmark
Popular version of paper 4aAO2
Presented Thursday Morning, June 8, 2006
151st ASA Meeting, Providence, RI
Spy-Hopping Norwegian killer whales-Photo by Fernando Ugarte. Used with permission.
Norwegian and Icelandic killer whales use a variety of techniques to get their dinner,
many of which are acoustic. In defense, their prey employ clever acoustical countermeasures
of their own. Icelandic killer whales, as we have discovered, employ an additional strategy,
apparently not shared by their Norwegian cousins, that may give them an extra advantage in
capturing their prey.
Killer whales of the Northeast Atlantic feed primarily on herring. In Norwegian waters
billions of herring migrate from open oceanic waters into deep fjords in the late fall
to over winter. Here they form vast schools that move up and down in the water column
in daily rhythms ?waiting? for spring to approach. In February, they migrate about 1,000
km south to their spawning grounds, and then out to open waters again. Groups of killer
whales follow the herring to cooperatively feed on this favored prey. Often the whales
dive to over a hundred meters to drive herring up to shallower waters forcing the fish
into tight groups by swimming around them and flashing their white bellies at them.
During this process the whales emit a cacophony of sounds (echolocation clicks, click
bursts, and whistles), some of which may help to tighten the herring school or coordinate
whale movements. At the right moment individual whales swim into the herd of fish and
perform underwater tail slaps that produce thud-like sounds and strong local water currents.
Many fish turn belly-up and remain motionless, apparently stunned by the tail slap.
Whales swim leisurely to the stunned fish and consume these one by one.
Click here
to see a film clip
Video by Fernando Ugarte. Used with permission.
What actually stuns the herring? We can only speculate at present, but the thud-like
sound produces an intense, bubble-producing (cavitation) pulse that may act like a blow
from a hammer. Rapid water movements may disorient the fish or the whale?s tail may
actually hit some fish. In any case some fish regain their orientation sense and swim away
normally after a few minutes.
Are the herring defenseless? Perhaps not: The swim bladder in fish is gas-filled and
helps to maintain neutral buoyancy and in herring it is connected to the intestine.
Herring forced toward the surface by a flock of killer whales can release air from the anus
producing a curtain of tiny bubbles around the school. This bubble curtain can act as a
screen for the whales? sonar clicks causing the school to suddenly disappear and perhaps
thwarting attack. In vernacular, "farting" may save their lives.
Icelandic killer whales may have refined their techniques for capturing herring.
They too use underwater tail slaps like their Norwegian relatives. The tail slaps have only
been heard and the consequences remain to be filmed although stunned herring rise to the
water surface above where whales are feeding. When listening to sequences of underwater
tail slaps from Icelandic killer whales we heard a long (about 3 seconds) tonal sound
(about 680 Hz) just prior (about 0.3 seconds) to the thud in about half of the tail slaps
(see picture 3 and listen to the sound). We never heard such tonal sounds in the tail
slaps of Norwegian killer whales.
Click here
to hear the sound clip
What could be the function of these tones? Could they communicate to other killer whales that
a slap was pending? We do not think so because the main energy in the tone is below
frequencies that the whales can hear well. Can herring hear the tone? The swim bladder of
the herring is connected to the inner ear, making hearing in this fish very sensitive.
Furthermore. the best hearing frequency of herring is around 700 Hz, or the resonant
frequency of the swim bladder at depths where they are preyed upon. So the herring can
certainly hear the tone produced by the killer whale.
What effect could the tone have on the herring? The killer whale tone is very intense
(170 to 190 dB at a distance of 1 m and a reference pressure of 1 microPascal) and could
force the school of herring to form a tighter ball making the tail slap more effective by
stunning more fish than otherwise possible
Therefore, North Atlantic killer whales -- and their herring targets -- make abundant use
of acoustics in their roles as predator and prey.
Some references:
- Enger, P. S. (1967). Hearing in herring. Comparative Biochemistry and Physiology 22, 527-538.
- Hall, J. D., Johnson, C. S. (1972). Auditory thresholds of a Killer whale
Orcinus orca
Linneaus. Journal of the Acoustical Society of America. 51: 515-517.
- Nøttested, L. (1998) Extensive gas bubble release in Norwegian spring-spawning herring (
Clupea harengus
) during predator avoidance. Journal of Marine Science 55:1133-1140.
- Similä, T. and Ugarte, F. (1993). Surface and underwater observations of cooperatively feeding killer whales in northern Norway. Canadian Journal of Zoology 71, 1494-1499.
- Simon, M., Wahlberg, M., Ugarte, F., Miller, L. A. (2005). Acoustic characteristics of underwater tail slaps used by Norwegian and Icelandic Killer whales (
Orcinus orca
) to debilitate Herring (
Clupea harengus
). Journal of Experimental Biology. 208: 2459-2466.
- Simon, M. Ugarte, F. Wahlberg, M. and Miller, L.A. (2006) Icelandic Killer whales (Orcinus orca) use a pulsed call suitable for manipulating the schooling behaviour of Herring (
Clupea harengus
). Bioacoustics (In Press).
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