DOSITS Videos2017-08-11T12:20:13+00:00

DOSITS Videos

The  videos in the tabs below were developed as brief introductions to some of the most commonly requested material on DOSITS. Below each video there is a list of key topics with associated links to DOSITS content for more in-depth material and an outline in PDF format.

These videos were sponsored by The Exploration and Production, Sound and Marine Life Joint Industry Programme – www.soundandmarinelife.org.

This video is an introduction to the science of sound.

Download the DOSITS Science of Sound Video outline (PDF)

Key topics/associated DOSITS links:

What is Sound?

  • Sound is created by a vibrating object.
  • Sound travels as a wave through a medium.
  • A sound wave is an example of a compressional or longitudinal wave.
    • The particles in a longitudinal wave move parallel to the direction in which the wave is traveling.
    • A sound wave alternately compresses (areas of high pressure) and expands (areas of low pressure) whatever medium it is traveling through.

For more information on the DOSITS website:

Characteristics of Sound

  • A sound wave’s amplitude relates to amount of energy it carries.
    • As amplitude increases, a sound is perceived to be louder; as amplitude decreases, a sound is perceived to be softer.
    • The average amount of energy passing through a unit area per unit of time in a specified direction is called the intensity of the wave. Sounds with higher intensities are perceived to be louder.
    • Relative sound intensities are often given in units named decibels (dB).
  • One complete repetition of a wave is called a [wave] cycle.
  • Frequency is the number of cycles per second.
    • If the frequency of a sound is increased (there are more cycles in a second), a higher pitched sound is produced. If the frequency is decreased, a lower pitched sound is produced.
    • A high-frequency sound has a shorter wavelength than a low-frequency sound. The wavelength is the distance from a point on one wave to the corresponding position on the next wave.
  • Phase specifies the location of a point within a wave cycle of a repetitive sound. When two sounds of the same frequency are in phase, their amplitudes combine. When they are out of phase, they cancel each other out.

For more information on the DOSITS website:

Sound Movement

  • Sound travels about 1500 meters per second in seawater. Sound travels much more slowly in air, at about 340 meters per second.
  • Sound level decreases as a sound moves away from its source. A sound wave gets smaller (loses energy) because it spreads out, or spreading loss occurs, and because some of the wave’s energy is absorbed.

For more information on the DOSITS website:

Source Levels/Ambient Noise

  • Background sound is the sum of all distance sounds in the ocean, called ambient noise.
    • The primary sources of ambient noise varies in different regions of the ocean and can be categorized by the frequency of the sound.
  • Source level is the intensity level of a sound source, at a distance of 1 meter. It has units of decibels.

For more information on the DOSITS website:

The Difference Between Sound in Air and Sound in Water

  • Sound waves in water and sound waves in air behave differently because of the physical differences between air and water.
    • The intensity of a sound wave depends not only on the pressure of the wave, but also on the density and sound speed of the medium through which the sound is traveling.
    • Sounds in water and sounds in air that have the same pressures have very different intensities because the density of water is about 800 times greater than the density of air.
  • Sound levels given in dB in water are not the same as sound levels given in decibels in air.

For more information on the DOSITS website:

This video is sponsored by The Exploration and Production, Sound and Marine Life Joint Industry Programme – www.soundandmarinelife.org.

This video is an introduction to Marine Mammal Hearing.

Download the Marine Mammal Hearing Video Outline (PDF)

Key topics/associated DOSITS links:

Marine mammal hearing

  • Hearing is the detection of sound. Both modern terrestrial mammals, including humans, and marine mammals evolved from ancestors that had air-adapted ears. Thus, many of the structures of the ear in both terrestrial and marine mammals are similar.
  • Some marine mammals that live exclusively in water hear very well in water but hear poorly, if at all, in air. Marine mammals that live on land at least part of the time, such as seals, sea lions and walruses, have ears that are amphibious and can hear in both air and water.
  • Hearing is the result of the combined activity of the ear’s three basic divisions:
    • The outer ear, which collects and directs sound;
    • The middle ear, which ear filters and transfers the acoustic energy to the inner ear; and
    • The inner ear, which transforms the acoustic energy to electrical signals to be processed by the brain.
  • There are many similarities in the basic hearing processes in marine mammals and terrestrial mammals. We will use the human ear as a model for terrestrial ears.
    • The outer ear includes the ear flap (or pinna), which funnels sound to the outer ear canal. The outer ear canal ends in the eardrum, or tympanic membrane, which separates the outer and middle ear.
    • The middle ear in terrestrial mammals is an air-filled space that contains a series of three small bones (or ossicles) called the incus (anvil), malleus (hammer), and stapes (stirrup). These bones are connected to the tympanic membrane and the oval window, which is the opening to the inner ear.
    • Sound energy from the outer ear causes the tympanic membrane to vibrate. The ossicles transform and amplify this energy at the tympanic membrane into vibrations to the fluid-filled cochlea via the oval window.
    • The cochlea, a spiral-shaped organ within the inner ear, transforms sound waves into nerve impulses. Membranes in the cochlea determine an animals’ hearing range and sensitivity.
    • As sound waves moves through the inner ear, the basilar and tectorial membranes vibrate. As the membranes move, fine stereocilia on the hair cells are bent, triggering a nerve impulse that conveys sound information to the brain.

For more information on the DOSITS website:

Marine mammal adaptations for hearing underwater

  • Scientists know that some amphibious marine mammals have mechanisms to close the outer ear canal.
    • When the animal is underwater, a valve clamps down on the outer ear canal, preventing water from entering.
    • Specialized middle ear tissues may also assist with pressure equalization during diving.
  • Adaptations for hearing underwater are really extreme in whales and dolphins. Instead of a normal outer ear canal, they have developed specialized fats that channel sound to the middle ear.
    • The jaw fats have different shapes and dimensions in each species, which are related to the frequencies of best hearing sensitivity.

For more information on the DOSITS website:

Hearing sensitivities of marine mammals

  • Like land mammals, each species of marine mammal has inner ears with membranes that respond, or resonate, according to differences in stiffness along the length of the ear canal. These differences determine their hearing ranges and sensitivities.
    • The largest marine mammals ears (e.g. gray whale) can hear infrasonics, that is, frequencies below 20 Hz. These large ears in baleen whales are specialized to hear well at very low frequencies.
    • Most marine mammals, however, have ears like the harbor porpoise that are able to hear best at ultrasonic frequencies, well above 20 kHz.
    • Typically, species that hear well at very high frequencies do not hear well at lower frequencies, below 500 Hz, which is where many human-generated sounds in the ocean occur.

For more information on the DOSITS website:

This video is sponsored by The Exploration and Production, Sound and Marine Life Joint Industry Programme – www.soundandmarinelife.org.

This video is an introduction to Hearing in Marine Fishes.

Download the Marine Fishes Hearing Video Summary (PDF)

Key topics/associated DOSITS links:

Physiology of hearing in marine fishes

  • All fish species detect particle motion, which is an oscillation back and forth along the line of transmission of a sound. Some fishes also have adaptations that let them detect sound pressure.
  • Fishes detect sounds with the inner ear, a structure that is very similar to parts of the ears found in terrestrial vertebrates and marine mammals. However, fishes have no need for external and middle ears since their bodies have approximately the same density as water, and sound passes right through their bodies to the inner ear.
  • Many fish species have calcium carbonate structures in the inner ear, called otoliths.
    • Each of these otolith organs differs in size and orientation.
    • The otoliths are also much denser than water and the fish’s body tissues, and vary in overall size and shape among species.
  • Each otolith organ consists of a solid mass, sitting on sensory hair cells. A sound propagates through the body tissues of a fish, and since the otoliths are denser, they move (or oscillate) at a different amplitude and phase in response to the sound waves than does the rest of the body tissues. The difference between the motion of the fish’s body and the otoliths causes cilia on the hair cells of the inner ear to bend. This difference between the motion of the hair cells and the otolith is interpreted by the brain as sound.
    • Each otolith organ has a different orientation, which, in addition to the variable orientation of the hair cells, enables sound direction to be determined.

For more information on the DOSITS website:

Hearing sensitivities of marine fishes

  • One factor affecting hearing sensitivity in fishes is the proximity of the inner ear to the swim bladder.
    • The density of the gas within the swim bladder is much lower than that of seawater and the fish’s body. As a result, sound waves cause the walls of the swim bladder to oscillate. If the movements of the swim bladder wall are transmitted to the ear, this results in the stimulation of the hair cells of the inner ear.
    • Fishes where there are direct connections between the swim bladder and other gas-filled organs and the inner ear, and even in some fishes without direct connections, have been shown to be sensitive to sound pressure.
  • Fishes lacking a swim bladder, or those that have a small or reduced swim bladder, or a swim bladder that is not in close proximity, or mechanically connected to the ears, are sensitive to particle motion.
    • These fishes can hear best when the levels of particle motion are especially high, for example, close to the surface or in shallow water.
    • They tend not to hear sounds at frequencies above 1 kHz.
  • Fishes with swim bladders that are in close proximity to the inner ear and/or are connected to the inner ear can hear at a wider frequency range than those fishes without such connections.
    • Some of these fishes can hear up to 3kHz or more.
    • One group, the clupeiform fishes, have gas ducts that extend from the swim bladder and come in direct contact with the inner ear. These ducts end in “bullae” that contain a gas bubble. The bubble is in close proximity to the inner ear, and results in the transformation of sound pressure waves to particle motion.
      • Some clupeid species, such as the American shad, can detect high-level ultrasonic frequencies up to 180 kHz.

For more information on the DOSITS website:

This video is sponsored by The Exploration and Production, Sound and Marine Life Joint Industry Programme – www.soundandmarinelife.org.

This video is an introduction to determining mitigation and monitoring through the ecological risk assessment process.

Key topics/associated DOSITS links:

Ecological Risk Assessment Process
The ecological risk assessment process is how scientists and decision makers examine potential risks related to human activities. These studies help regulators and managers make important decisions, including determining if there are mitigation and monitoring activities that could be conducted to reduce the potential for ecological effects to occur.

The first stage of the process is to define the problem.

The next stage of the process involves two steps:

  • estimating the probability of an animal being exposed to the problem
  • determining the types of ecological effects that might be expected

Based on the results of these analyses, the final stage, estimating potential ecological effects, can be completed.

When applying the ecological risk assessment process to underwater sound produced from a sound source, it is important to estimate a source’s sound field to determine if and/or the amount of exposure of marine animals to the sound.

For more information on the DOSITS website:

Sound Field
A source’s sound field is a snapshot in time of the level of sound at different distances and depths as the sound travels away from the source. The sound field only exists when sounds are transmitted. How often a source transmits and how long the signals are will affect the amount of exposure marine animals might get.

For more information on the DOSITS website:

Effects of Sound
In addition to considering the sound field, scientists must also consider whether or not a particular species is found in the area at the time of year that the sound source is being used and whether the species is sensitive to the sounds being transmitted. By coupling the animals with the sound field, the amount of exposure can be estimated to determine what potential effects might occur.

For more information on the DOSITS website:

Measure Marine Mammals Reaction to Sound
Methods are being applied or developed to help measure and predict the potential effects of underwater sound on marine animals, which include:

Many factors influence the potential effects underwater sounds may have on marine animals and how scientists monitor, measure, and mitigate sound sources.

This video is sponsored by The Exploration and Production, Sound and Marine Life Joint Industry Programme – www.soundandmarinelife.org.