Daniel and Marcelo: Your video provides much needed documentation and may provide further insight to what we have long proposed may be occurring especially in calm surface conditions and slow vessel speeds. Acoustical spreading loss (from the propellers at the stern to the bow), and acoustical shadowing, together with Lloyd's mirror effect would have made this vessel acoustically undetectable to the whale in direct line with the approaching ship. At this speed spreading losses alone could have easily attenuated the propeller noise at the bow below that of the whale's auditory critical ratio's for the prevailing ambient noise. As slower speed reduces propeller source levels, it also lowers the frequency spectra of the noise. Simple spreading losses would have reduced these already modest noise levels down another 40+ dB at the bow. Acoustical shadowing and Lloyd's mirror effect significantly block and attenuate the dominant lower frequency noise at the bow and near the surface. The confluence of these propagation factors would have made the sounds of this approaching container ship, (as it does for most traditional stern propeller configurations), indiscernible from the ambient noise (even in relatively quiet ambient conditions). Here is a web link which addresses this problem and a parametric directional alarm developed to help mitigate the risks of ship strikes by directly addressing the very real acoustical detection challenges whales face. This is a lay paper published and hosted by the Acoustical Society of America as a multimedia link which illustrates and demonstrates the detection problem. http://www.acoustics.org/press/157th/gerstein.html For additional information I have attached a paper published in 2005 in IEEE. proceedings which details some of the acoustical challenges associated with ship whales. The acoustics of vessel collisions with marine mammals Gerstein, E.R. Blue, J.E. Forysthe, S.E. This paper appears in: OCEANS, 2005. Proceedings of MTS/IEEE Publication Date: 2005 On page(s): 1190- 1197 Vol. 2 ISBN: 0-933957-34-3 INSPEC Accession Number: 9006048 Digital Object Identifier: 10.1109/OCEANS.2005.1639917 Posted online: 2006-06-26 09:31:15.0 Regards, Edmund Gerstein, President Leviathan Legacy Inc 1318 SW 14th Street Boca Raton, Florida 33486 gerstein@aol.com 561-338-9185 Director Marine Mammal Research Charles E Schmidt College of Science Behavioral Sciences Building Florida Atlantic University 777 Glades Road Boca Raton, Florida 33431 egerste1@fau.edu 561-809-9185 -----Original Message----- From: Daniel Pérez Martínez <daniel.reporte@gmail.com> To: marmam@lists.uvic.ca Sent: Thu, Aug 5, 2010 8:14 pm Subject: [MARMAM] Southern right whale ship srike in Peninsula Valdes Dear colleagues On August 3 at 15:00 pm. a container vessel collided with a southern right whales when is was arriving to a pier (Storni) of the city of Puerto Madryn. The incident occurred at a time when the ship Langeness 160 meters lenghts, at very low speed entering collided with bulb bow to an individual of right whale about 200 meters from the pier. We filmed and photographed the incident. Pictures and video could be seen and/or downloaded at http://bioreporte.com/bahia/08/2010/cargo-vessel-strikes-a-southern-right-wh... Kind Regards and please could you be so kind to respond directly to our E-mail address, Daniel Pérez Martínez Independent consultant Daniel.reporte@gmail.com Domec García Norte 1142 (9120) Puerto Madryn (Chubut) Argentina Dr. Marcelo Bertellotti Biología y Manejo de Recursos Acuáticos Centro Nacional Patagónico (CONICET) bertello@cenpat.edu.ar Boulevard Brown 2825 (9120) Puerto Madryn (Chubut) Argentina _______________________________________________ ARMAM mailing list ARMAM@lists.uvic.ca ttps://lists.uvic.ca/mailman/listinfo/marmam