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Sounds recorded during the cooperative hunt may be prey fish alarm call

Posted by pbio on 07 May 2009 at 22:14 GMT

Author: Joseph Luczkovich
Position: Associate Professor
Institution: East Carolina University
Additional Authors: Mark Keusenkothen
Submitted Date: December 06, 2006
Published Date: December 10, 2006
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

We have analyzed the sound track of a video that was submitted as part of the supporting material for the report of interspecific cooperative hunting by reef fishes by grouper (Plectropomus pessuliferus) and giant moray eels (Gymnothorax javanicus) as reported by Bshary et al. (2006). We can identify several sounds in these recordings, including snapping shrimps (Alpheus or Synalpheus sp.), the SCUBA diver's bubbles and breathing, but we note that a clearly identifiable biological sound of unknown origin occurred between 3-5 s on video clip (Video S2), while the grouper and giant moray eel were swimming together. An analysis of this recorded sound was performed using the signal processing routines in Matlab 7 and an oscillogram and spectrogram was produced. We would gladly provide these analyses to the editors for publication, although anyone listening to the sound track of Video S2 can hear the sounds. This sound did not appear to be associated with any signaling behavior by the grouper or moray eel. We did not hear this sound while the grouper was signaling in the first video clip (Video S1). The "grunting" sound was recorded twice during the video, when the divers’ breathing is not dominating the recording. The sound has a dominant frequency of approximately 400 Hz and a pulse repetition rate of 7 pulses in 0.25 s. The grunting is similar to those we have recorded in Belizean reefs by squirrelfish (Holocentrus sp.), which also hide in reef crevices during daytime; however, we cannot positively assign this sound to that genus without confirmatory recordings from fish known to occur at the reef investigated by Bshary et al. (2006). We suspect that the prey fish that was being hunted by the grouper and moray eel was producing the sounds, perhaps as a threat display or warning call to other fish. However, we cannot rule out the possibility that the grouper or the moray eel made the sounds, or that some other fish made the sounds. The authors observed the fish prey consumed by the grouper and moral eel in several cases, but do not report the species of fish that were captured. We wonder if the authors noted which prey were present in the video (Video S2 in particular) and if that species is known to make sounds. Observations of sounds of fishes and the associated behavior are rare in the literature (Rountree et al. 2006), and the behavior associated with a sound often suggests a function of sound production. The close association of the grunting sound with the unusual cooperative hunting behavior suggests a co-relationship between hunting and sound production in the two species or their prey that should be further investigated.

Bshary R, Hohner A, Ait-el-Djoudi K, Fricke H (2006) Interspecific communicative and coordinated hunting between groupers and giant moray eels in the Red Sea.
PLoS Biol 4(12): e431. DOI: 10.1371/journal.pbio.0040431.

Rountree, R. A., R. G. Gilmore, C. A. Goudey, A. D. Hawkins, J. J. Luczkovich, D. A. Mann. 2006. Listening to Fish: Applications of Passive Acoustics to Fisheries Science. Fisheries 31(9): 433-446.

No competing interests declared.