Shallow water acoustics and marine mammals

Abstract

Human activity is causing significant changes to the shallow water acoustic environment. A good understanding of the basics of shallow water acoustics is essential to a proper assessment of the impact of this activity on marine mammals. Misunderstanding of the relevant underwater acoustics can often lead to erroneous conclusions about the impact of such changes on marine mammal ecology. This paper will address some of the issues and misunderstandings. Shallow water regions present an acoustic environment which is typically much more demanding and complex than the deep water environment. Propagation is strongly influenced by the surface, water column, and sea bottom and will vary greatly from place to place, and time to time. Shallow water regions are highly reverberant and are often very noisy. Marine mammals rely on underwater sound for communication and detection of prey. Unlike fish, which evolved entirely in the sea, the marine mammals auditory system evolved from a terrestrial auditory system. This paper will also address the differences between shallow water acoustics and atmospheric and deep water acoustics, and how they effect the acoustic behavior of marine mammals. Specific adaptations of the dolphins echolocation system to the shallow water environment are highlighted.