OUR WATER RESOURCE QUIZ

							Week 3                                                                                  Module 7:
Day 4                                                                                      Noise

                                        Discussion Topics

   1.   Can the Navy’s sonar systems drown out the songs of whales?
   2.   Is this dangerous to the whales?
   3.   What do whales use sound for?
   4.   What are the background sound levels in the ocean?
   5.   What are other man-made loud sound levels in the ocean?
   6.   What are the other marine mammals that depend upon sound?
   7.   How do marine mammals hear?
   8.   What are the differences in the hearing between marine mammals and humans?

See Ref 4 for information concerning these discussion positions. First introduce the types of
marine mammals. If time does not allow focus on the Cetaceans section of ref 4, pp 2-3. The
chapters in ref. 4 that are particularly relevant to these discussion positions include:

              Chapter 5 – Ambient Noise (in the Sea)
              Chapter 6 – Man-Made Noise (in the Sea)
              Chapter 7 – Marine Mammal Sounds
              Chapter 8 – Marine Mammal Hearing
              Chapter 11 – Significance of Responses and Noise Impacts

                             How Loud is Sound Underwater ?
                 Decibels Underwater Are Not The Same As Decibels In Air!

To understand environmental issues that affect marine mammals underwater, the definition of
the decibel units for measuring noise or sound must be understood. Confusion often results
because of the unit of measurement underwater is different from sounds measured in air. Both
air and water use the decibel (dB) unit, but the reference in air is 20 microPascals and water is 1
microPascal. Rules-of-thumb for equivalence, then, are 160 dBwater ≈ 100 dBair and 125 dBwater ≈
65 dBair

Example Units Conversions

Week 3, Activity 10: The Hearing Curve (Humans and Marine Mammals)

Ref. 1, pp 59-64. Ref. 6, pp 108-126. Ref 4, pp 205-238




                                              7B-13