EFFECT OF NOISE ON MARINE MAMMALS THE ITS ENVIRONMENT

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CHAPTER 1: INTRODUCTION

This chapter of the research tends to develop an understanding and identify the reasons for conducting a research onto the identified topic. However, in the context of this paper this chapter would inculcate the notions relating to the effects of noise on marine mammals along with its environment. Moreover, the chapter also intends to develop an effective and efficient understanding of how noise tends to reflect upon marine mammals. On a broader context this chapter will equip the reader to understand the primary notions as far as the whole context of effects of noise in concerned.

Background of the Problem

Ambient noise in most areas of the ocean is dominated by noise from commercial shipping'. Underwater radiated noise is an incidental by-product from standard ship operations, with highest sound levels at low frequencies. The sounds generated by ships consists of a broad-band component from propeller cavitation and narrow band tones from propeller cavitation and internal machinery. This low-frequency noise can propagate long distances depending on where the ship transits. Sound is recognized as a critical, if not primary, sensory system for many marine organisms (MacArthur, Geist & Johnston 1982, p. 351-358).

Sound energy travels efficiently through the ocean medium, and marine animals have evolved systems to exploit this property for communication during social and breeding activities, navigation, habitat selection, sensing and tracking prey and predators. The introduction of man-made sound into the marine environment threatens these basic life strategies by masking signals from specifics and predators, altering behavior, and inducing negative physiological responses. On an ocean basin scale, low-frequency background noise attributed to bourgeoning commercial shipping has been increasing by three decibels per decade (a doubling in acoustic energy). thus , raising concerns about the impacts on marine life. The world's oceans are threatened by complex and interacting anthropogenic activities, however, very few areas are unaffected by humans.

Noise from commercial ship traffic is a dominant component of the low-frequency ambient noise in the deep ocean; yet, the contribution of ship noise in coastal regions is more difficult to predict because of environmental variables and varying contributions of ship noise. The variability in ship noise is related to the proximity to shipping lanes and local sound propagation conditions, unlike deep water sites where distant shipping dominates ambient noise levels. Distant shipping does not contribute to ambient noise at many coastal sites because of sound scattering and shadowing effects from bathymetric features. The level of noise radiated by an individual ship or ship-type and the spatial extent are important factors to consider when evaluating the contribution of ship noise to sites on the continental shelf. As described above, noise levels from an individual ship do not simply correlate with the size and speed of the ship.

Therefore, the noise levels in a coastal region will depend on the types of ships present and the variables that will influence propeller (source) depth (Erbe 2002, 394- 418). Combining acoustic measurements of ship noise with ship traffic composition and ...