André, M., Johansson, A.T., Delory, E., van der Schaar, M., Morell, M. Foraging on squids: the sperm whale mid-range sonar 19th Conference of the European Cetacean Society, La Rochelle, France, 2005 Résumé: It has been long speculated about the sperm whale sonar capabilities. While the usual clicks of this species are considered the support of mid-range echolocation, no physical characteristics of the signal have clearly confirmed this assumption nor have explained how sperm whales forage on squids. The recent data on sperm whale on-axis recordings have allowed us to simulate the propagation of a 15kHz pulse as well as its received echoes from different targets taking into account the reflections from the bottom and the sea surface. The analysis was performed in a controlled environment where the oceanographic parameters and the acoustic background could be modified. We also conducted experimental measurements of squid target strength (Loligo vulgaris and Sepia officinalis) to further investigate and confirm the TS predictions from the geometric scattering equations. Based on the results of the computer simulations and the TS experimental measurements (TS squid = - 36.3 ± 2.5dB), we were able to determine the sperm whale sonar minimum requirements, i.e. range and directional hearing, to locate a single 24.5cm long squid, considered to be from stomach contents the major size component of the sperm whale diet. Here, we present the development of the analysis which confirms that sperm whale usual clicks are appropriate to serve a mid-range sonar function allowing them to forage on individual low sound-reflective organisms. Projet: Noise pollution effects on cetaceans