Clicking for calamari : toothed whales can echolocate squid Loligo pealeii

This study was funded by the Oticon Foundationwith additional support from Reson, and a Steno scholarshipto P.T.M. from the Danish Natural Science ResearchCouncil. M.W. was funded by a PhD scholarship from theFaculty of Natural Sciences at Aarhus University and the PhDSchool SOAS. R.T.H. acknowledges partial funding fromNOAA/NURP grant UAF-05-0133.

Squid play an important role in biomass turnover in marine ecosystems and constitute a food source for ~90% of all echolocating toothed whale species. Nonetheless, it has been hypothesized that the soft bodies of squid provide echoes too weak to be detected by toothed whale biosonars, and that only the few hard parts of the squid body may generate significant backscatter. We measured the acoustic backscatter from the common squid Loligo pealeii for signals similar to toothed whale echolocation clicks using an energy detector to mimic the mammalian auditory system. We show that the dorsal target strengths of L. pealeii with mantle lengths between 23 and 26 cm fall in the range from –38 to –44 dB, and that the pen, beak and lenses do not contribute significantly to the backscatter. Thus, the muscular mantle and fins of L. pealeii constitute a sufficient sonar target for individual biosonar detection by toothed whales at ranges between 25 and 325 m, depending on squid size, noise levels, click source levels, and orientation of the ensonified squid. While epipelagic squid must be fast and muscular to catch prey and avoid visual predators, it is hypothesized that some deep-water squid may have adopted passive acoustic crypsis, with a body of low muscle mass and low metabolism that will render them less conspicuous to echolocating predators.

Author Posting. © Inter-Research, 2007. This article is posted here by permission of Inter-Research for personal use, not for redistribution. The definitive version was published in Aquatic Biology 1 (2007): 141-150, doi:10.3354/ab00014.