These noises are also highly uneven and are characterized as spontaneous (such as seismic surveys) and “tonal (such as sonar), comparatively loud (such as explosives) and relatively quiet (such as most fishing activities), persistent (such as shipping), short (such as winches) and very short (such as a single seismic survey pulse).”Explosions, Naval low frequency active sonars (LFA), some mid-frequency active sonars, high-power seismic surveying systems that are utilized to explore the ocean floor for oil and natural gas resources and commercial ships can all be discover over large distances, sometimes beyond oceans. (Hatch & Wright, 2007)
Man-made sounds are created both purposefully and ...view middle of the document...
On the contrary, some physiological and behavioural responses are reversible (Aguilar de Soto, 2013). Due to a number of beaked whale stranding events associated with military use of mid-frequency sonar in the area, the possibility of permanent or even lethal injury in marine mammals has received considerable attention in the scientific and public spheres. Routine anthropogenic sounds in the underwater consisting of seismic surveys, pile driving or chemical explosions; leads to extensive disturbance of normal behaviour by marine mammal species (Department of Arts, Heritage and the Gaeltacht, 2012). Marine mammal exhibits diverse impacts are including: changes in vocalisations, behavioural changes in diving and foraging; noise and stress, beaked whale stranding, shipping and masking of signals, and hearing damage. Some of the extensively researched responses are detailed in this paper:
Noise and Stress in Marine Mammals
Few studies have been reported to demonstrate the possible relationship between noise and stress in marine mammals. Noise is associated with increase level of stress hormones which in turns lead to the induction of physiological stress. Four captive beluga whales (Delphinapterusleucas) were exposed to playbacks of drilling noise in the study by Thomas, Kastelein & Awbrey (1990), however, “no changes in blood adrenaline and noradrenaline (stress hormones, also known as epinephrine and norepinephrine) levels measured immediately after playbacks were found.” (Wright et al, 2007) No changes in the level of stress hormone are due to the insensitive measures. Another research by Romano et al. (2004) subjected a captive beluga whale and bottlenose dolphin to noise from a seismic water gun and (for the bottlenose dolphin) 1-s, 3-kHz pure tones. Different hormones in the blood were analysed, including cortisol, before and after exposure and results conclude changes and disruptions (especially with the seismic sound) that were considered detrimental. (Wright et al, 2007).
Changes in Vocalisation
When the surrounding noise interferes with the sound, the animal will experience increase in vocalization with the aim to overcome masking. Signal’s quality of information and ranges over which these signals can be heard are both reduced via masking. Belugas at St. Lawrence River also reveal to intensify the level of their vocalisation as a reaction to increase in the levels of shipping noise, an indication of a Lombard vocal response. More whistles are produced by pilot whales (Globicephalamelas) as a feedback to military mid-frequency sonar whereas bottlenose dolphins (Tursiopstruncatus) display the same response when exposed to boat approaches. (Weilgart, 2007)
Decrease in vocalization has also been observed in response to noise, halting to call entirely for periods of weeks or months in marine mammals. This can have intimation for “breeding, feeding, or social cohesion, depending on the...