May 26 2011

Acoustic Effects – Marine Mammals

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Marine mammals rely more on sound over visuals due to light quickly being absorbed in salt water while sound has the ability to propagate efficiently through water (Hammond 36). Mammals have the potential to be affected by any manmade noise they are naturally sensitive to, ranging from mild irritation, to disruption of social interactions or even physical injury and death (Hammond 36). Many marine mammals rely on low frequencies for their intraspecies calls including grey seals and baleen whales; however others, such as tooth whales, have a better high frequency hearing (Hammond 37-39). Therefore, any range of frequency has the potential to affect a type of marine mammal.

Harbor porpoises, as well as several other cetacean species, use auditory senses as their primary sense (Lucke 17). Therefore, they will be among the most effected by sounds produced by energy generators. However, porpoises have also been found to respond to disturbance by flight, moving away from approaching vessels (Hoffman 32). While no studies have been done on their reaction to ocean energy generators (Hoffman 32) their reaction to other manmade noise could indicate that any noise produced by manmade ocean energy generators would displace porpoises, causing a change in the ecosystem make-up.  Additionally, windmills specifically are expected to generate noise considerably above ambient levels, potentially affecting the communication of porpoises that remain (Hoffman 33). Their functional hearing ranges from 250 Hz to 160 Hz, with most sensitivity around 100 Hz to 140 Hz (Lucke 17). Lack of communication could affect the purposes’ abilities to mate or defend one another, making them more susceptible to predators. Porpoises also use low frequency clicking sounds, around 1.4 Hz to 2.5 Hz for echolocation which enables them to find prey, spatial orientate themselves, and navigate (Lucke 17). Any manmade sound produced around these frequencies could affect the ability of purposes to feed or navigate. Unless they adjust to the sound, harbor purpose numbers could decline in areas of energy generators due to either avoidance or inability to take care of basic needs. However, testing is needed to determine the extent of the effects that energy generators would cause.

Porpoise’s hearing anatomy


The harbor seal produces underwater sounds between 8 kHz and 150+ kHz, mostly at 12-40 kHz (Hoffman 33). Again, any manmade sound that produces frequencies around these levels could affect their echolocation and social interactions (Hoffman 33). A particularly important frequency to harbor seals is that around 350 Hz which is used by the harbor seal mother to recognize and maintain contact with her pup (Hoffman 33). The survival rate of harbor seal pups could then decline if frequencies around this level are produced. Like harbor porpoises, seals typically react to disturbances by moving away. Conversely, as long as the sounds do not produce significant consequences for the seal, they have the ability to habituate quickly to repeated stimuli (Hoffman 34). Therefore, the overall effects of sound from energy generators on seals are expected to be negligible (Hoffman 34).

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4 Responses to “Acoustic Effects – Marine Mammals”

  1.   good childrenon 06 Jun 2013 at 8:00 am


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