Glossary
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"dinner bell" effect
when an underwater sound (or some other stimulant) acts like a dinner bell, alerting and attracting an animal to the presence of a food source.

A

A-weighting
the most commonly used frequency weighting function for humans that accounts for the fact that human hearing is less sensitive to low frequencies; units dB(A) or dBA.
absorption
the conversion of acoustic energy to heat energy
acceleration
the rate of change of velocity with respect to magnitude or direction.
accelerometer
a device that measures the vibration, or change in motion (acceleration) of a structure or organism. The force caused by vibration or a change in motion causes piezoelectric material within the device to be squeezed, which produces an electrical charge that is proportional to the force exerted upon it. Since the charge is proportional to the force, and mass remains constant, the charge is also proportional to the acceleration.
accuracy
the degree of closeness of measurements of a quantity to its actual value.
acoustic fish tag
a transmitter implanted or attached to a fish to monitor fish movement
acoustic impedance
the amount of sound pressure generated by a given vibration at a specific frequency.
acoustic modem
a wireless communication device used to transmit data and information through the ocean
acoustic propagation models
conceptual and numerical models that compute how sound travels through the water, taking into account many variables such as water temperature, salinity, bottom topography, etc.
acoustic release
a device which holds onto the anchor of a buoyant instrument until it is commanded to release it
acoustic telemetry
to transmit acoustic signals automatically and at a distance, as between a ground station and an artificial satellite, space probe, or the like, especially in order to record information, operate guidance apparatus, etc
acoustic threshold
the received level at which an effect from acoustic exposure may begin to occur.
acoustic tomography
uses the travel time of sound in the ocean to measure the temperature of the ocean over large areas
acoustic trauma
severe traumatic injury from sound
acoustical shadowing
a condition that occurs when refraction or reflection prevents direct sound waves from reaching a region (called a shadow zone)
active acoustics
sound is purposefully generated and received
adaptation
an alteration in the structure or function of an organism or any of its parts that results in the organism becoming better fitted to survive and multiply in its environment.
ADCP
Acoustic Doppler Current Profiler; an instrument used to measure the current using acoustic sound and the knowledge of the Doppler effect
agonistic behavior
aggressive or defensive social interaction (such as fighting, fleeing, or submitting) between individuals usually of the same species
airgun
An airgun is designed to release compressed air, which forms bubbles. The formation of bubbles produces a loud sound that is used to explore the geologic structure of the ocean floor. Airguns primarily produce sound at low frequencies (between 10-500 Hz); however, high frequency noise is also created. A small airgun that releases 0.16 Liters of air can create source amplitudes up to 216 underwater dB at 1 meter. A large airgun that releases 32.8 Liters of air can have a source level of up to 232 underwater dB at 1 meter.
algorithm
a step-by-step procedure for calculations/solving a problem.
alongshore flow
A surface current that flows parallel to the shore.
Amazon river dolphin
Inia geoffrensis
ambient noise
background sound in the ocean. Examples of sound sources contributing to ambient noise include waves, wind, rain, shrimp, earthquakes, volcanoes, and distant sources, such as shipping and airguns.
American lobster
Homarus americanus
American shad
Alosa sapidissima
amphibious
living or able to live on land and in the water
amplitude
the maximum distance that a vibrating particle moves from its equilibrium; how much the medium is disturbed
anadromous
migrating from salt water into fresh water to breed/spawn (i.e. salmon are anadromous).
anemometer
a weather instrument that measures wind speed.
angle of incidence
the angle that the incident wave makes with a line perpendicular or normal to the reflecting surface
angle of reflection
the angle that the reflected wave makes with a line perpendicular or normal to the reflecting surface
animated frequency spectrum
An animated frequency spectrum is a series of frequency spectra that show just the frequencies present at each moment in time. You can see what frequencies are associated with each part of a sound.
anthropogenic
caused by humans
Aristotle's lantern
claw-like mouth on a sea urchin that contains five calcium carbonate teeth that are used for feeding
array elements
a single hydrophone in a receiving array or a single projector (sound source) in a projector array
arthropods
invertebrates of the phylum Arthropoda that have jointed appendages and a chitinous, segmented exoskeleton. Arthropods include insects, spiders, crabs, and lobsters.
Atlantic croaker
Micropogonias undulatus
Atlantic mackerel
Scomber scombrus
Atlantic salmon
Salmo salar
Atlantic spotted dolphin
Stenella frontalis
Atlantic Undersea Test and Evaluation Center (AUTEC)
a deep-water laboratory located in the Bahamas (in the Tongue of the Ocean (TOTO)) that is instrumented with a variety of acoustic beacons and sensors to provide testing, evaluation, and certification for U.S. Navy submarine captains and their crews, as well as the accuracy of their undersea weapons. A Marine Mammal Monitoring (M3R) system has been established at AUTEC to monitor vocalizing animals via the 91 range hydrophones.
attenuation
the decrease in the intensity of a wave due to the loss of acoustic energy to heat energy
audiogram
a graph expressing hearing loss (hearing sensitivity) as a function of frequency
audiometric curve
a graph displaying the range of sounds that humans can hear.
auditory brainstem response (ABR)
Whenever a sound wave is detected by the ear, it triggers a number of neuro-physiological responses along the auditory pathway. An auditory brainstem response test is an objective test that measures the electrical potential produced in response to sound stimuli by the synchronous discharge of the first through sixth order neurons in the auditory nerve and brainstem. Also sometimes known as brainstem auditory evoked potential (BAEP) or brainstem auditory evoked response (BAER).
auditory bulla
a hollow, bony structure that encloses parts of the middle and inner ear.
auditory fatigue
when the intensity level or duration of sound overwhelms the hair cells so they cannot respond to sounds appropriately
auditory meatus or ear canal
an air-filled canal that leads from the ear flap to the ear drum. It helps direct sound waves to the ear drum.
auditory system
the sensory system for hearing, consisting of the ear and the central nervous system.
auditory weighting function
a mathematical equation that compensates for the fact that animals do not hear equally well at all frequencies.
Australian freshwater crayfish
Cherax destructor
Automatic Identification System (AIS)
an automated tracking system used to electronically identify and locate ships. AIS uses GPS-linked, very high frequency radio signals that allow for ship-to-ship and ship-to-shore information transfer. Information transmitted includes a ship's name, position, speed, heading, and other information. These details are transmitted multiple times each minute.
autonomous
existing and/or functioning independently; with regards to underwater vehicles, one which travels underwater without requiring input from an operator.
axial muscles
folded muscle segments that, when contracted, produce a wavelike motion that moves the fish through the water

B

backscatter
the deflection of sound in a scattering process through an angle greater than 90 degrees. Backscatter is the term commonly used to describe the return of sound from the seafloor to the receiver in an active sonar.
Baiji
Lipotes vexillifer
baleen
series of horny plates that hang from the gums of the upper jaw of some large whales (called Mysticetes). The baleen is made from the same materials as human hair and fingernails. It is used to filter small bits of food from the water.
baleen whales
These large cetaceans are usually more than 9.1 m (30 ft) long and can be found throughout the ocean. Instead of teeth, mysticetes have a series of horny plates called baleen. The baleen is made from the same materials as human hair and fingernails. The baleen plates hang from the gums of the upper jaw and are used to filter small bits of food from the water. Baleen whales have symmetrical skulls and have two (or paired) blowholes.

The mysticetes are divided into four families: rorquals (blue, humpback, minke, sei, fin, and Bryde's whales), right whales, pygmy right whales, and gray whales. Rorquals have throat pleats, or ventral grooves, that expand when the whales gulp large amounts of water during feeding. Baleen whales can migrate up to hundreds of miles to feed in cooler areas with lots of food. On the feeding grounds baleen whales filter out small organisms from the water either by skimming the surface or gulping large quantities of water to filter. Baleen whales are not known to echolocate but produce a variety of sounds used for communication. Echoes from baleen whale vocalizations may help in navigating under ice or detecting the ocean floor.
Barth’s myochordotonal organs (Barth’s MCO)
thin-walled sensory organ found in the exoskeleton on each leg of semi-terrestrial ocypodid crabs.
basilar membrane
a membrane in the cochlea of the ear that vibrates in response to sound. As sound vibrations progress down the ear, a fluid wave that is created by the movement of the third ossicle, the stapes, moves the basilar membrane. The basilar membrane is the part of the cochlea that separates sounds according to their frequency.
basking shark
Cetorhinus maximus
bathymetry
charting of the sea floor using water depth measurements
Bathythermograph
an instrument that makes a record of the temperature at various depths in the ocean
beacon
an acoustic signaling device that continually sends out a repetitive signal. Acoustic beacons, sometimes called pingers, are used to mark the locations of underwater objects.
beam pattern
a graphical or other description of the response of a transducer used for sound transmission or reception as a function of the direction of the transmitted or incident sound waves.
beamforming
a general signal processing technique used to control the directionality of the reception or transmission of a signal on an array of sensors. Using beamforming during sound transmission, the majority of signal energy is transmitted in a specified direction. During sound reception, beamforming allows sensors to predominantly receive energy from a specified direction
bearded seal
Erignathus barbatus
bearing
measurement of direction; the angle, with respect to magnetic north, to where the target is located
bel
a unit used in the comparison of power levels or of intensities of sounds corresponding to an intensity ratio of 10:1.
beluga whale
Delphinapterus leucas
benthic
living on the bottom of the sea (or a lake).
biologically significant
an action or activity that affects an animal's ability to grow, survive, or reproduce.
biomass
measure of the amount of living material in an area, usually expressed in units of weight per unit volume
bivalve
an aquatic mollusk that has a compressed body enclosed within a hinged shell, such as oysters, clams, mussels, and scallops.
black drum
Pogonias cromis
black rockfish
Sebastes melanops
Blainville's beaked whale
Mesoplodon densirostris
blue rockfish
Sebastes mystinus
blue shark
Prionace glauca
blue whale
Balaenoptera musuculus
blue whiting
Micromesistius poutassou
blue-fin tuna
Thunnus thynnus
bottlenose dolphin
Tursiops truncatus
bowhead whale
Balaena mysticetus
bowriding
a common activity of dolphins and other cetaceans in which marine mammals swim in front of a vessel, riding or surfing on the pressure wave created by the vessel
broadband
a sound signal that includes acoustic energy across a wide range of frequencies.
bubble feeding
a feeding process where whales trap a school of prey (fish or krill) by blowing a series of bubbles as the whales swim to the surface. The bubbles form a curtain that rises to the surface of the water and concentrates the prey in the center. The whales charge through with their mouths open to engulf the fish or krill.
bubble frequency
the frequency equal to the reciprocal of the time interval between the shock wave and the first bubble pulse.
bubble pulses
secondary shock waves of explosions in which the bubbles repeatedly grow larger and smaller.
buccal cavity
the anterior portion of the oral cavity, also sometimes referred to as the vestibule or entry area of the oral cavity. It is the region bounded by teeth and gums, jaws, and cheeks.
buoyancy
the upward force on a free floating or submerged object, independent of the object's weight; gives submerged objects the weightless appearance.
burst-pulse sounds
a rapid series of broadband clicks similar to those used in echolocation, but with a much shorter interclick interval of 0.5-10ms. Given this very high pulse repetition rate, greater than 300 pulses/second, more clicks are produced per unit time with burst-pulsed sounds.
bycatch
the harvest of fish (or any marine organism) other than the species for which the fishing gear was set
byssal threads
string like substance that is secreted by mussels to allow the mussel to attach to hard substrates like rocks

C

C-weighting
a frequency weighting function that was originally designed to predict the human ear’s sensitivity to tones at high noise levels; however, nearly all noise measurements for hearing conservation are measured with A-weighting; units dB(C) or dBC.
caldera
depression formed at the summit of a volcano
California mantis shrimp
Hemisquilla californiensis
California sea lion
Zalophus californianus
callosities
thick, white patches of hardened skin, called chitin, that are covered with tiny crustaceans, called "whale lice." These patches are found on the heads, over the eyes, and around the mouths of whales, particularly right whales and bowhead whales. The patterns created by the patches are used by marine mammal researchers to identify individual whales.
calve
the sudden release and breaking away of a mass of ice from a glacier, iceberg, ice front, or ice shelf.
canine teeth
sharp, fang-like teeth adapted for capturing and penetrating prey
Cape fur seal
Arctocephalus pusillus
capillaries
the smallest of the network of blood vessels throughout an organism
carapace
hard, protective outer case or shell that covers the back or part of the back of an animal (as in a turtle or a lobster).
cardioid
a heart-shaped curve generated by a point on a circle that rolls without slipping on another fixed circle of the same diameter.
Caribbean spiny lobster
Panulirus argus
caudal peduncle
The narrow part of the body to which the caudal fin (or tail) attaches to the body.
cavitation
formation of gas-filled cavities in liquids in motion when the pressure is reduced to a critical value. Low pressure regions are often created by rotating ship propellers. As the propellers rotate, bubbles form in the water. A loud acoustic sound is created when these bubbles collapse.
central nervous system
the complex of nerve tissues that controls the activities of the body. In vertebrates it comprises the brain and spinal cord.
cephalopod
class of soft-bodied invertebrates that includes octopuses, squids, nautiluses and cuttlefishes. These animals have many arms and well-developed eyes.
cetacean
order of mammals that includes whales, dolphins and porpoises
characteristic impedance
a material property of a medium, defined as the density of the medium times the sound speed through the medium.
cheliped
the first two claws of a crab. A male fiddler crab has an enlarged claw or cheliped.
chordotonal organs
for Crustaceans, they are located at the joint segments and they serve as mechanoreceptors (sensory organs).
cichlids
family (Cichlidae) of freshwater fishes found throughout tropical and subtropical waters of the Americas, Africa and parts of Asia
cilia
hair cells of the neuromast
cleaner shrimp
Periclimenes longicarpus
click
a short pulse of sound, often used to describe pulses produced by toothed whales for echolocation.
click train
rapid sequence of clicks, produced by whales and dolphins, that are associated with echolocation. The clicks are emitted from the melon of the whale.
climatologist
a scientist who studies climate
clupeids
fish belonging to the herring family
coalesced
fused or grown together
cochlea
the spiral-shaped chamber within the inner ear that transforms sound waves into nerve impulses. The cochlea is a fluid-filled organ that houses many structures related to hearing, including the basilar membrane and the organ of Corti. It is considered "the organ of hearing."
cod
Gadus morhua
coda
patterned set of clicks produced by sperm whales. Each sperm whale may have its own individually distinct coda pattern.
common carp
Cyprinus carpio carpio
common dolphin
Delphinus capensis (long-beaked common dolphin), Delphinus delphis (short-beaked common dolphin)
common octopus
Octopus vulgaris
common prawn
Palaemon serratus
communication space
the area over which one individual can detect the signal of another.
Comprehensive Nuclear-Test-Ban Treaty
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions on Earth whether for military or for peaceful purposes. It was adopted by the United NAtions General Assembly in 1996. The treaty contains provisions for monitoring which include acoustic monitoring. The treaty is not yet in force because it has not been ratified by some nations.
compression wave
a wave propagated by compressing the medium; longitudinal wave
Computerized Tomography (CT)
method of constructing a three-dimensional image of an object from narrow x-ray beams that are passed through the object from several angles
conductive hearing loss
transmission of sound to the inner ear is impaired
conductivity-temperature-depth (CTD)
Oceanographic tool used to determine the essential physical properties of sea water: conductivity (salinity), temperature, and depth. Depth measurements are derived from measurement of hydrostatic pressure and salinity is measured from electrical conductivity. The CTD may be incorporated into an array of sampling bottles referred to as a "carousel" or "rosette". The sampling bottles close at predefined depths, triggered either manually or by a computer, and the water samples may subsequently be analyzed further for biological and chemical parameters.
conspecific
animals (or plants) belonging to the same species
controlled experiments
tests or experiments used to demonstrate a cause and effect relationship. Results from tests performed on an experimental sample (which receives a particular treatment) are compared to those from a control sample (which does not receive the treatment) with all other aspects of the experiment remaining the same between the two groups.
convergence zone
a region of high intensity created by the refraction of sound waves in the SOFAR channel transmitted by a source near the sea surface. Convergence zones occur at about the same depth as the source approximately every 50-60 km away from it.
coronet
a star-shaped ossified crest mounted in a socket-like base
correlation
a relationship between two variables during a period of time, especially when there is a close match between the variables' movements. Correlation may indicate association between the variables; however, it does not mean that there is a cause and effect relationship.
corticosteroid
a type of hormone produced by the adrenal glands. Corticosteroids levels may be elevated as a response to stress.
courtship
behaviors in animals, that are used to initiate mating
critical habitat
specific geographic area(s) that contains features essential for the conservation of a threatened or endangered species and that may require special management and protection.
crustaceans
a class of mainly aquatic, gill-breathing arthropods such as crabs, lobsters, shrimp, and barnacles. They usually have a hard exoskeleton and two pairs of antennae.
cupula
gel-like cover of cilia in the neuromast
Cuvier's beaked whale
Ziphius cavirostris
cylindrical spreading
energy spreading out from a sound source in the shape of a cylinder; no energy radiates above the top or below the bottom of the cylinder

D

dB peak
a unit of relative pressure when the pressure of the sound wave is characterized as the peak pressure.
dB peak-peak
a unit of relative pressure when the pressure of the sound wave is characterized as the peak-to-peak pressure.
decibel
a relative unit used to describe sound intensities. Written as dB. See Advanced Topic: Introduction to Decibels.
decompression sickness
known as the bends, a condition that occurs in deep-sea divers caused by the formation of nitrogen bubbles in the blood and tissues following a sudden decrease in the surrounding pressure. This occurs when ascending rapidly from a deep dive and is characterized by severe pains in the joints and chest, skin irritation, cramps, and paralysis.
delphinid
cetaceans of the family Delphinidae, the most diverse of cetacean families. Includes oceanic whales and dolphins, such as, killer whales, pilot whales, common dolphins and bottlenose dolphins
depredate
the removal and/or damage of netted or hooked fish and bait from fishing gear.
derived
formed or developed from something else; not original. NOTE: different areas of science have more specialized definitions for this term (e.g. in paleontology, derived characteristics means something has evolved to fit a particular pressure).
detection probability p(D)
the probability of correctly deciding on the basis of a statistical test that a signal is present when it is in fact present.
detection threshold
the signal-to-noise ratio (SNR) (in decibels) required to achieve a specified probability of detection p(D) for a given probability of false alarm p(FA) when deciding whether or not a signal is present at a receiver.
detonation
to explode
dialect
vocalizations or calls of cetaceans that are characteristic of a particular group or pod
DIFAR
Directional Frequency Analysis and Recording device; passive acoustic sonobuoy
digital data
information that is represented in a coded form, as a series of zeros and ones
directional
producing or receiving sound only from certain angles or directions
displacement
the linear distance in a given direction between a point and a reference position.
distribution
the frequency of occurrence of a specific value in a set of measurements.
diurnal
of or during the day.
doppler effect
the raising or lowering of the frequency of a sound due to the motion of the source of the sound relative to the listener. The most common example is the rising frequency of a train whistle as the train approaches.
dorsal
of or pertaining to the upper surface.
dorsal fin
the main fin found on the back of fishes and some marine mammals. Some whales, such as the killer whale, have tall dorsal fins, while other whales (i.e. belugas and bowheads) have no dorsal fin.
drumming
to vibrate a muscle in, on, or near, the swim bladder that produces a loud, low-pitched grunt sound
ducts
internal passage involved in the flow of fluids through an organism
Dugong
Dugong dugon
duration
the length of a sound in seconds

E

echinoderm
marine invertebrates with tube feet and five-part radially symmetrical bodies. The group includes sea urchins, sea stars, sea cucumbers, brittle stars, and crinoids.
echo ranging
Determining the distance to an object by measuring the time between transmitting a sound signal and hearing its echo.
echo signature
a unique sonar return (reflection) that can be used to identify individual species of marine organisms, such as fish, or other submerged objects
echolocation
a process for locating distant or hard-to-see objects using the reflection of sound waves. The distance of objects or depth of the seafloor can be determined by measuring the time it takes for reflected sound waves (echoes) to return to the sound source. Some whales and dolphins use echolocation to identify underwater objects and to help find food.
echosounding
the technique of measuring the depth of a body of water by means of an echosounder, an electrical depth sounder that uses sound echoes. The instrument emits sound waves that travel to the bottom of the ocean and are reflected back. Depth is determined by timing how long it takes the sound pulse to leave the instrument, travel to the seafloor, and return to the receiver on the ship.
ecological risk assessment
the process of calculating the probability of adverse ecological effects
ecology
the scientific study of the relationship between organisms and their environment.
ecotype
Ecologically distinct groups or communities; in this case, groups exhibiting different dietary specializations and corresponding behavioral adaptions, such as hunting techniques and acoustic repertoires.
elasmobranch
a group of cartilaginous fish that comprises the sharks, rays, and skates.
elasmobranchs
a group of fishes, including sharks, rays and skates, that has a skeleton made of cartilage rather than bone; they also do not have a swim bladder.
electro-physiological response
the electrical activity of neurons when stimulated (see auditory brainstem response (ABR)).
elephant seal
Mirounga
endangered
any species that is in danger of extinction
endemic
Native to or prevalent in a particular area or region; not found in other places.
entanglement
whales, seals, sea lions, and other marine animals may come into contact with lost or active fishing gear, causing the gear to become twisted around their bodies and/or snagged on different body parts. When this occurs, the animal is considered entangled.
epicenter
the point on the earth's surface (on land or underwater) vertically above the focus of an earthquake.
equal energy hypothesis
assumption that sounds of equal SELcum produce an equal risk for hearing loss (i.e., if the SELcum of two sources are similar, a sound from a lower level source with a longer exposure duration may have similar risks to a shorter duration exposure from a higher level source).
equal latency
the assumption in hearing studies that sounds that are perceived to be equally loud result in equal response times, thereby allowing response time to be a proxy for perceived loudness.
equal loudness curve
a graph of the perceived intensity (loudness) of sounds. The loudness of a sound is different for different frequencies.
equilibrium
the rest position of the particles in a medium
essential fish habitat (EFH)
those waters and substrate necessary for fish for spawning, feeding, or growth to maturity.
estuary
a coastal body of water formed when freshwater from rivers and streams flows into the ocean, mixing with the seawater. Estuaries and the lands surrounding them are places of transition from land to sea, and from freshwater to saltwater. Although influenced by the tides, estuaries are protected from the full force of ocean waves, winds, and storms by the reefs, barrier islands, or fingers of land, mud, or sand that surround them.
euphausiids
small, shrimp-like invertebrates (also called krill ) that swarm in dense patches within the water column or at the sea surface. They have hard mouths and tail parts that reflect sound. Krill is an important food source for many marine organisms including whales and seals.
European perch
Perca fluviatilis
European spiny lobster
Palinurus elephas
exoskeleton
A hard outer structure, such as the carapace of a lobster or crab, that provides protection or support for an organism (especially invertebrates).
expendable bathythermograph
A probe which is dropped from a ship and measures the temperature as it falls through the water. Two very small wires transmit the temperature data to the ship where it is recorded for later analysis. The probe is designed to fall at a known rate, so that the depth of the probe can be inferred from the time since it was launched. By plotting temperature as a function of depth, the scientists can get a picture of the temperature profile of the water.
explosive sound source
a device that uses explosive material to generate controlled acoustic energy.
extinction
The end of an organism or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to reproduce and recover may have been lost before this point).
extirpation
the movement of an entire population out of a region
extrapolate
to estimate or expand unknown data based on known facts and/or observations.
extrapolation
using evidence and inferences from a similar situation to project information about a related event or process. Extrapolation can also be used to apply or transfer experimental observations from a model to the real world.

F

false alarm
incorrectly deciding on the basis of a statistical test that a signal is present when it is in fact absent. A false positive.
false alarm probability p(FA)
the probability of incorrectly deciding on the basis of a statistical test that a signal is present when it is in fact absent.
false killer whale
Pseudorca crassidens
false negative
an error when one concludes that there is not a real difference between two means when, in fact, there is a difference; also called a Type II error.
false positive
an error when one concludes that there is a real difference between two means when, in fact, there is not; also called a Type I error.
fat emboli
a fat globule in the bloodstream that is often caused by physical trauma such as fracture of long bones, soft tissue traum, or burns.
fathead minnow
Pimephales promelas
fecund, prolific
fruitful in offspring or vegetation
fiddler crabs
Uca rapax
fin Whale
Balaenoptera physalus
finfish
teleost bony fishes, in other words, not sharks/skates/rays, and not shellfish.
finless porpoise
Neophocaena phocaenoides
fishery
the industry or occupation devoted to the catching, processing, or selling of fish, shellfish, or other aquatic animals.
fishes
two or more fish species. For example, if you have three fish species in an aquarium (such as a clownfish, damselfish, and goby), you would say "three fishes." If you have three clownfish (all of the same species), you would say "three fish."
fluke
the two lobes of a whale tail.
focal animal observations
observations concentrated on individual animals that record everything they do
foraging
to search for food
foraging behavior
the way in which an animal searches for food; the process, or series of actions, that an animal goes through to find food
Franciscana dolphin
Pontoporia blainvillei
frequency
the rate of repetition of a regular event. The number of cycles of a wave per second. Expressed in units of Hertz (Hz)
frequency spectrum
a graph of a sound that plots the intensity of each frequency in the sound. Plural is spectra.
frequency weighting
a method for quantitatively compensating for the fact the animals do not hear equally well at all frequencies within their hearing range.
fright response
responding out of fear
fundamental frequency
the lowest frequency of a harmonic series. The fundamental frequency is also called the first harmonic frequency (f) of a harmonic series.

G

ganglion cells
nerve cells that have their cell bodies outside of the central nervous system (the brain and spinal cord). Auditory ganglion cells carry sound information from the inner hair cells to the auditory nerve.s
gas gland
a modification of the inner lining of the bladder, which works with the rete mirabile to force gases into the bladder
goldfish
Carassius auratus auratus
goliath grouper
Epinephelus itajara
gray triggerfish
Balistes capriscu
gray whale
Eschrichitus robustus
great white shark
Carcharodon carcharias
green sea turtle
Chelonia mydas
green sea turtle
chelonia mydas
grey seal
Halichoerus grypus
gross tonnage
a measure of the cargo carrying capacity or the volume of a ship.
gudgeon
Gobio gobio

H

habituate
to become accustomed to something through repeated or prolonged exposure
haddock
Melanogrammus aeglefinus
hair cells
mechano-transducers that detect energy or pressure changes. They are complex structures that include a cell body on the surface of a membrane. At the base of the hair cell are one or more neural synapses. On the upper surface of the hair cell are hair-like projections called stereocilia, commonly in bundles. These stereocila bend in response to a range of stimuli based on the species, some from fluid motion, some in association with crystals or otoliths, some because of being embedded in a second membrane. When these stereocila bend, they trigger a release of chemicals that initiates the electrical signal (neural impulse) that is carried to and processed by the brain.
harbor porpoise
Phocoena phocoena
harbor seal
Phoca vitulina
harmonic distortion
distortion of a pure tone associated with the presence of undesired harmonics at frequencies that are a multiple of the fundamental frequency of the signal.
harmonic frequency
the part of a signal whose frequency is an integer multiple of the fundamental frequency. Harmonic frequencies are related to each other by simple whole number ratios, for example if the fundamental frequency is f, the harmonics have frequencies of 2f, 3f, 4f, etc.
hawaiian monk seal
Monachus schauinslandi
Heard Island Feasibility Test (HIFT)
an expedition to Heard Island in the southern Indian Ocean during which acoustic sources suspended below a ship transmitted acoustic signals to receivers around the globe. Heard Island was selected because signals transmitted from that location can reach both coasts of North America. HIFT showed that underwater acoustic signals could be received worldwide and serve as a method for measuring global ocean warming.
hearing generalist
a fish species in which the swim bladder aids very little or not at all in hearing sensitivity
hearing groups
groups of marine mammals defined by the generalized range of frequencies that species in the group can hear.
hearing range
the range of frequencies the ear of an animal can detect.
hearing specialist
a fish species in which the swim bladder is directly connected to the inner ear and provides increased hearing sensitivity
hemorrhages
flow of blood from a ruptured blood vessels; excessive bleeding
hermaphroditic
an animal or plant having both male and female reproductive organs
Hertz
the unit of frequency; the number of cycles, or wavelengths, in a second (cycles/second)
hierarchy
a system or organization in which people, animals, or groups are ranked one above the other according to status or authority.
histogram
a representation of a distribution by means of rectangles whose widths represent class intervals and whose areas are proportional to the corresponding frequencies of occurrence.
homologous
similar in position, structure, and evolutionary origin but not necessarily in function.
humpback whale
Megaptera novaeangliae
hydraulic hammer
a large, industrial hammer that is operated by a fluid that is under pressure (hydraulics). A hydraulic hammer is a modern type of piling hammer used in place of diesel and air hammers for driving steel pipe, precast concrete, and timber piles.
hydroacoustic
acoustics in water
hydrodynamic
of, relating to, or operated by the force of liquid in motion
hydrofoil
a vessel that is lifted partially above the water by wing-like structures mounted on struts below the hull of a boat.
hydrophone
an underwater microphone that will listen to, or pick up, acoustic signals. A hydrophone converts acoustic energy into electrical energy and is used in passive underwater systems to listen only.
hydrophone array
several hydrophones attached to each other at known fixed distances so the location of sound sources can be calculated
hydrostatic pressure
The pressure at a point in a fluid at rest due to the weight of the fluid above it.
hydrothermal
relating to hot water circulation in the ocean crust.
hydrothermal vent
a hot spring on the seafloor
hyperthermia
a condition where the body produces or absorbs more heat than it can dissipate, causing one's body temperature to become elevated to a potentially dangerous level.
hypothesis
A tentative explanation proposed by a scientist for observations that cannot be explained by existing scientific theories. A careful statement of a tentative or provisional conclusion to be tested.

I

ice keel
the underwater portion of an ice ridge.
IES
Inverted Echosounder; an instrument used to measure the temperature of the water column at a single point
immunological response
a bodily defense reaction that recognizes an invading substance (such as a virus, fungus, or bacteria, or a transplanted organ) and produces antibodies specific to that invading substance.
impulsive sound
a broadband signal generated by sound sources such as explosions and airguns in which the sound pressure is very large at the instant of the explosion and then decays rapidly away; the duration of the peak pressure pulse is usually only a few milliseconds.
incident wave
the wave moving towards the reflector
infrasonic
sound waves that have a frequency that is lower than what humans can hear (i.e. below about 20 hertz). Baleen whales, such as blue and fin whales, produce these low frequency sounds. The sounds may be used to communicate over long distances and to detect large-scale topography of the seafloor. On land, elephants also use these powerful infrasonic sounds to communicate over long distances.
inner ear
the innermost part of the ear that is surrounded by the skull bone. It contains the organs of balance and hearing. The inner ear contains the vestibular system that helps maintain our balance. It also contains the cochlea that transforms sound waves into nerve impulses that are carried to the brain.
intensity
the average amount of sound power (sound energy per unit time) transmitted through a unit area in a specified direction. The unit of intensity is watts per square meter. For simplicity, the magnitude of the intensity is often referred to as the intensity, without specifying the direction in which the sound is traveling.
inter-click interval
the time it takes an echolocation signal to be sent out and an echo to return, combined with the time the animal needs to receive and process that echo.
invertebrate
an animal that lacks a backbone (marine examples include lobsters, shrimp, squid, clams, crabs, and sea stars).
ion
an atom or a group of atoms that has an electric charge. Positive ions, or cations, are formed by the loss of electrons; negative ions, or anions, are formed by the gain of electrons.

K

kelp rockfish
Sebastes atrovirens
kerplunks
technique used by dolphins to drive fish away from protected areas such as sea grass beds. A dolphin will lift its tail and lower body out of the water and crash it down on the water surface. This causes a loud splash and creates a trail of bubbles under the water. The bubbles startle the fish hiding in the seagrass and flush them from their hiding places, making it easier for the dolphin to detect them.
killer whale
Orcinus orca
Kina
Evechinus chloroticus
kinetic energy
the energy possessed by a system or object as a result of its motion.
knots
a unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph.
krill
small, shrimp-like invertebrates (also called euphausiids) that swarm in dense patches within the water column or at the sea surface. They have hard mouths and tail parts that reflect sound. Krill is an important food source for many marine organisms including whales and seals.

L

labyrinth
a complex system of interconnecting bony or membranous cavities, particularly those concerned with hearing and balance
ladyfish
Elops saurus
lanugo
the soft, downy hair that covers some newborn mammals; in Arctic seals, it is a white fur that is highly prized by seal hunters, most famously associated with the hunting of harp seal pups
laryngeal sac
an inflatable “pouch”, or often a pair of pouches, that are generally located ventral to the larynx in many mammals, particularly in primates (but not in humans), hooved mammals (e.g., reindeer, horses, antelopes), and cetaceans. The functions of laryngeal sacs are not completely understood. Like the vocal sacs of frogs, laryngeal sacs may amplify calls but in some species, they may assist extended, rapid vocalizations by acting as air reservoirs.
larynx
the upper part of the trachea (air passage) that contains the vocal folds
lateral line
sensory organ, found in fishes, that runs long the length of their body. The lateral line allows fish to sense movement.
leopard seal
Hydrurga leptonyx
leopard shark
Triakis semifasciata
ligaments
strong, flexible bands of tissue that hold two or more bones together at moveable joints. They help restrain the movement of bones at the joint.
little skate
Raja erinacea
localize
determine the direction the sound is coming from.
LOFAR
Low Frequency and Ranging sonobuoy; a type of passive acoustic sonobuoy
logarithmic
of, relating to, or expressed in terms of logarithms. A logarithm is the power to which a base, such as 10, must be raised to produce a given number.
Lombard Effect
the unconscious tendency of a person or animal to raise and/or lower their voice when going from a relatively quiet to a noisy environment and vice versa
Long-spined sea urchin
Diadema setosum
longfin squid
Loligo pealeii
longitudinal wave
a disturbance in which the particles and the energy move in the same direction
loudness
how loud a person perceives a sound to be. Not the same as the intensity of the sound. The perceived loudness varies with frequency.
lunge-feeding
a method of feeding underwater in which the predator moves forward with its mouth open, engulfing the prey along with the water surrounding it.
Lusitanian toadfish
Halobatrachus didactylus

M

magnetic resonance imaging (MRI)
method of producing a three-dimensional image of object by recording the signals the object emits when placed in a magnetic field
manatee
Trichechus spp.
mandible
one of the jaw structures of animals. For example, in vertebrates, it is the lower jaw bone; in insects it is one of the anterior mouth parts.
masking
acoustic interference that reduces the ability to detect, recognize, or understand sounds of interest.
mass stranding
a stranding event where 2 or more animals, excluding mother-calf pairs, unless a third animal strands, strand together in time and place.
mean
the average of a set of measurements defined to be the sum of all of the measurements divided by the number of measurements.
mechanoreceptors
sensory organs that cause response to displacement, pressure and vibrations
medium
substance or material that carries or transports the wave from its source to other locations. In the open ocean, the medium through which the wave travels is the ocean water.
melon
lipid-filled sac in the forehead of whales that helps to focus sound
mesopelagic boundary community
small (less than 4 inches long) fishes, shrimps, and squids that live in the middle of the water column and near islands
metamorphosis
the process of transformation from an immature form to an adult form.
mid-ocean ridge
underwater mountain chain where new ocean crust is created.
middle ear
the air-filled cavity that lies between the outer ear and the inner ear. The middle ear contains the ossicles which conduct sound vibration from the eardrum to the inner ear.
migration
movement of a group of animals from one location to another
minke whale
Balaenoptera acutorostrata
miss
Incorrectly deciding on the basis of a statistical test that a signal is absent when it is in fact present. A false negative.
mitigate
to make (something) less severe or harmful.
molt
to shed the outer covering, or shell, which is then replaced by a new shell that is produced by the organism
mooring
equipment (often consisting of anchors and chains) which holds an item (such as a boat or underwater instrument) stable and secure in one place
morphology
the form and structure of an organism or any of its parts
mudflat fiddler crab
Uca rapax
multi-channel seismics
using multiple hydrophone arrays or streamers to record the reflected and refracted sounds from an air gun array
Mysticetes
These large cetaceans are usually more than 9.1 m (30 ft) long and can be found throughout the ocean. Instead of teeth, mysticetes have a series of horny plates called baleen. The baleen is made from the same materials as human hair and fingernails. The baleen plates hang from the gums of the upper jaw and are used to filter small bits of food from the water. Baleen whales have symmetrical skulls and have two (or paired) blowholes.

N

narial passages
the air spaces that connect the throat region with the openings of the nose, known as the nares. It is also sometimes referred to as the nasal passages.
narrowband
sounds made up of only a small range of frequencies
narwhal
Monodon monoceros
natal
grown, produced, or originating in a particular place or in the vicinity (of, relating to, or present at birth).
necropsies
the examination and dissection of a body to determine the cause of death; autopsy
NeMO Net
New Millennium Observatory Network; a project, which records and transmits daily temperature and pressure readings from Axial Volcano
Neural impulses
An electrical and chemical signal sent along nerve fibers
neuromasts
small, sensory receptors of arranged hair cells located along the lateral line, which respond to motion between the fish and the surrounding water
new england mussel
Mytilus edilus
noise
an unwanted sound or a sound that interferes with the perception of another signal, whether it be through recording or hearing.
non-vocal sounds
sounds made without the use of vocal folds or other body parts whose primary function is moving air for sound production. These sounds are typically made by slapping a body part on the water or land surface, or by forcefully clapping body parts together. Non-vocal sounds may be used to communicate acoustically.
normal line
a line that is perpendicular (makes a 90 degree angle) to a surface
North Atlantic right whale
Eubalaena glacialis
North Pacific right whale
Eubalaena japonica
Northern bottlenose whale
Hyperoodon ampullatus
Northern elephant seal
Mirounga angustirostris
Northern fur seal
Callorhinus ursinus
Northern seahorse
Hippocampus erectus
Northern shrimp
Pandalus borealis
Norwegian herring
Clupea harengus
null decision
correctly deciding on the basis of a statistical test that a signal is absent when it is in fact absent.
null hypothesis
the hypothesis that there is not a real difference between the means of two data sets.

O

ocean observatory
a networked array of sensor systems that measure the physical, chemical, geological and biological variables in the ocean and seafloor as well as the overlying atmosphere.
oceanographic variable
a characteristic of the ocean that changes
octave band noise
noise over a range of frequencies where the frequency in Hertz of the upper end of the range is twice the frequency of the lower end
octavo-lateralis system
comprised of the lateral line and inner ear of fish; provides fish with balance, hearing, and the ability to feel vibrations from a distance
odontocete
group of mammals that includes the toothed cetaceans. This includes some whales (such as sperm whales, orca or killer whales, and beaked whales) as well as all dolphins and porpoises.
offspring
next generation or baby of a certain species
olfactory organ
an organ for smelling
omnidirectional
having no directional component; producing or receiving sounds from all directions
omnivorous
organisms that eat both animals and plants
opportunistic feeding
a type of foraging in which an animal feeds on a wide variety of prey and is able to adapt to whatever food becomes available.
oral cavity
the mouth, which forms the first chamber of the digestive system. It includes the space surrounded by the lips, teeth, hard and soft palates, cheeks, and tongue. The oral cavity ends at border of the pharynx, which is approximately the line just anterior to the tonsils.
organ of Corti
the sensory part of the inner ear that converts sound signals into nerve impulses. Located on the basilar membrane, it contains sensory cells that transform vibrations into neural code for sound processing by the brain. It contains many important cells including the inner and outer hair cells.
oscar
Astronotus ocellatus
ossicles
three tiny bones - the incus (anvil), malleus (hammer), and stapes (stirrup) - that lie in the middle ear. The ossicles conduct sound across the middle ear to the inner ear by forming a bridge between the eardrum and the oval window.
otariids or eared seals
fur seals and sea lions that have visible ear flaps. They have an elongated neck and long front flippers. Their hind flippers can be turned forward for walking on land.
otolith
small bones in the inner ear which provide balance, and, in fish, aid in hearing
ototoxic
causing damage to the ear or its nerve supply.
outer ear
the outermost part of the ear that is external to the ear drum or tympanic membrane. It directs sound waves down the air-filled ear canal onto the eardrum.
oval squid
Sepiotheutis lessoniana
oval window
a membrane-covered opening between the middle ear and the inner ear. The oval window is connected to the third ear ossicle (stapes) and passes sound vibrations to the inner ear.
overpressure
The pressure in the shock wave from an explosion that exceeds the existing atmospheric or hydrostatic pressure in the medium through which the shock wave is propagating.
oyster toadfish
Opsanus tau

P

Pacific humpback dolphin
also known as the Indo-Pacific humpback dolphin; Sousa chinensis
Pacific Missile Range Facility (PMRF)
a U.S. Naval facility off the island of Kauai, Hawaii, that is the world's largest instrumented, multi-dimensional testing and training missile range. It is the only range in the world where submarines, surface ships, aircraft, and space vehicles can operate and be tracked simultaneously. There are over 1,100 square miles of instrumented underwater range and over 42,000 square miles of controlled airspace. Additional bottom-mounted hydrophones are being installed at PMRF in early 2011, and similar to AUTEC and SCORE, a Marine Mammal Monitoring (M3R) system is being installed to monitor vocalizing animals.
Pacific white-sided dolphin
Lagenorhynchus obliquidens
pack ice
a large expanse of floating ice
pan bone
thin bone in the back of the lower jaw that helps transmit sound to the middle ear
parallel
being an equal distance apart everywhere, extending in the same direction, never meeting or intersecting
particle motion
the change in position of a particle with respect to time; in acoustics, particle motion is vibratory motion in which the particles move back and forth around an equilibrium point.
passive acoustics
listening to sound sources; sound is only received
peak pressure
the range in pressure between zero and the greatest pressure of the signal.
peak pressure/0-to-peak pressure
the range in pressure between zero and the greatest pressure of the signal
peak-to-peak pressure
the range in pressure between the most negative and the most positive pressure of the signal
pectoral fins
the uppermost of the paired fins on a fish
pectoral flipper
forelimbs of whales and dolphins that are used for stability and steering. These appendanges are generally flattened and paddle-like. Humpback whales have very large pectoral flippers, reaching 5 m (15 ft) in length.
pectoral free rays
rays that are part of the fishes pectoral fins but are free from the actual fin skin. These rays aid in the movement of the fish.
pectoral girdle
the bony or cartilaginous arch that supports the forelimbs of a vertebrate
peer reviewed
scientific papers that have been subjected to evaluation by highly qualified experts in the field, the reviewers are usually anonymous and check the papers for inconsistencies, invalid conclusions and editorial errors
peer-reviewed
a process by which a scholarly work (such as a paper or a research proposal) is checked by a group of experts in the same field to make sure it meets the necessary standards before it is published or accepted
pelagic
of, relating to, or living or occurring in the open ocean.
pelagic species
organisms that swim or drift in the water; these organisms are distinct from those living on or in the bottom sediments.
perceive
to recognize, discern, or understand.
permanent threshold shift (PTS)
a permanent increase in the threshold of hearing (minimum intensity needed to hear a sound) at a specific frequency above a previously established reference level
perpendicular
being at right angles
pharyngeal
teeth located in the gill or throat region
phocids or true seals
seals, such as harbor seals, that have no visible ear flap. They have a streamlined body with short front flippers. Their hind flippers are directed backward and they are not used for walking on land.
phon
a unit of loudness for pure tones that accounts for the perceived loudness of tones; the number of phon of a sound is the decibel of a sound at 1 kHz that is perceived to be just as loud.
photophores
light producing organs that appear as bright spots on various marine animals, including fishes and cephalopods.
physiological stress
a reaction to a change that requires a physical, mental or emotional adjustment or response.
piezoelectric effect
the ability of some materials (notably crystals and certain ceramics) to generate electricity in response to applied mechanical stress
piezoelectric material
a material that produces electrical charges when subjected to pressure changes
pilot whale
Globicephala spp.
ping
to query (another computer on a network, or in this case, an acoustic transponder) to determine the location of it.
pink snapper
Pagrus auratus
pink snappers
Pagrus auratus
pinna, auricle
the ear flap or outer part of the ear that extends from the head. The pinna funnels sound down the outer ear canal to the eardrum.
pinniped
group of mammals that includes seals, sea lions and walruses
pitch
an up-or-down movement of the front (bow) of a vessel (ship, glider, etc.).
plainfin midshipman
Porichthys notatus
plane wave
a wave in which the wave fronts are a series of parallel planes.
plankton
relatively small organisms that drift or float passively in the water and are carried wherever currents and tides take them. Plankton are often microscopic and are an important food source for other aquatic organisms. There are two types of plankton- phytoplankton (plants and autotrophs) and zooplankton (animals).
plectrum
part of the spiny lobster that is found underneath the files. It is a soft piece of tissue that is found at the base of the antennae. The plecta is what the lobster pulls over the files to produce sound
pneumatic
containing or operated by air or gas under pressure.
pod
a social group of whales that are clustered together. Some toothed whales, such as orcas travel in large, sometimes stable pods. They may group together to hunt their prey and/or migrate.
polar bear
Ursus maritimus
polar bear
Ursus maritimus
pollack
Pollachius pollachius
polyps
small marine invertebrates that have hard, cup-like, limestone skeletons. Polyps live in large colonies where they take-in the calcium from the ocean and to build a hard shell around themselves. The skeletons grow one on top of one another and as a result a coral reef is able to grow.
population
the entire collection of individuals or items from which samples are drawn.
power
the probability of rejecting the null hypothesis in a statistical test when it is false.
precision
the degree to which repeated measurements under unchanged conditions show the same results; reproducibility; repeatability.
prehensile
adapted for seizing, grasping, or holding, especially by wrapping around an object.
pressure
the amount of force per unit area measured in units of atmospheres (atm)
profile
the change of an oceanographic variable with water depth
projector
an instrument that sends out sound waves; consists of a transmitter and a transducer
projector arrays
a collection of individual projectors used together to generate a directional sound beam
propagation
the movement of sound through a medium.
pulse
a short duration broadband signal.
pure tone
a sound that consists of one single frequency

Q

queen parrotfish
Scarus vetula

R

RAFOS floats
floating instruments designed to move with a current and track the current's movements
rainbow trout
Oncorhynchus mykiss
ramp-up
gradually increasing the sound source level
rarefaction
The instantaneous, local reduction in density of a gas or other medium resulting from passage of a sound wave.
receiver
something that listens for or receives sound; it may or may not record the sound
receiver-operating-characteristic (ROC) curve
a curve that plots the cumulative distribution functions of the false-alarm probability and the detection probability on the x-axis and y-axis, respectively, to select the optimal detection threshold.
recess
hole, corner or niche. For example, a rock recess, a place surrounded by rocks where a fish can hide
rectified diffusion
when acoustic energy causes supersaturated gas to be pumped into an existing small bubble, making the bubble increase in size
red drum
Sciaenops ocellatus
red grouper
Epinephelus morio
reflected wave
the wave moving away from the reflector
reflection
the deflection of the path of a sound wave by an object or by the boundary between two media
reflector
any boundary between two media that causes the reflection of a wave
refraction
the bending of a sound wave towards a region of slower sound speed
repertoire
Suite of behaviors that an animal may use in different contexts; in this case, the number of call types that have been distinguished based on categorization of vocal behavior.
resonance
when sounds of specific frequencies cause air- or fluid-filled organs to vibrate with amplitudes that are large compared to the amplitude of incoming soundwaves
resonator
something that fills with sound and acts as a natural amplifier
rete mirabile
a tightly packed bundle of capillaries which works with the gas gland to force gases into the bladder
reverberation
echo
ringed seal
Phoca hispida
rip current
A strong, narrow surface current that flows rapidly away from the shore, returning the water carried shoreward by waves.
Risso's dolphin
Grampus griseus
roll
the rotation of a vessel about its longitudinal (front/back) axis.
root-mean-square pressure
the square root of the average of the square of the pressure of the sound signal over a given duration. Root-mean-square is often abbreviated rms
rorquals
whales of the family Balaenopteridae which includes humpbacks, sei, minke, fin, blue and Bryde's whales. They have throat pleats or ventral grooves that expand when the whales gulp large amounts of water while feeding.
rostrum
upper jaw of whales that is elongated and looks like a beak

S

sablefish
Anoplopoma fimbria
saithe
Pollachius virens
salinity
the total amount of salt dissolved in seawater; the units most often used are parts per thousand (ppt) but practical salinity unit (psu) is now the accepted standard in oceanography. An average salinity value for seawater is 35 ppt (psu) or 35 parts of salt in 1000 parts of water.
salt domes
a layer of salt in a domed structure that was formed beneath the Earth's surface by the movement of salt over long periods of time. Salt domes are often associated with oil and gas deposits.
sample
a subset of the population.
sample size
the number of individuals or items in a subset or sample of the population from which estimates of various statistical measures of the whole population are calculated.
sand fiddler crab
Uca pugilator
sardines
small, silvery, slender fish of the herring family that have one short dorsal fin and no scales on their heads
Sargassum or Gulfweed
a type of brown algae (of the genus Sargassum) that have a branching thallus (body) with lateral outgrowths differentiated as leafy segments, air bladders, or spore-bearing structures
scattered/scattering
the diffusion of the sonar signal in many directions through refraction, diffraction and reflection, primarily due to the material properties of the seafloor. Scattering is one of the causes of attenuation in sonar, resulting in signal weakening.
scatterer
a particle in seawater or the roughness on the sea surface or seafloor that causes sound energy to be scattered
scattering
when the path of a sound wave is broken up by objects (volume scattering) or the sea floor or sea surface (boundary scattering)
school
a large group of marine animals, for example fish, that swim together. The appearance of a large number of individuals may ward off potential predators.
Sciaenidae
family of fishes that contains approximately 270 species distributed in the Atlantic, Pacific, and Indian Oceans. This family is commonly known as the drums, which are renowned for their sound producing ability.
scientific method
the orderly process by which scientists ask questions about the natural world and test their observations
sea otter
Enhydra lutris
sea state
condition of the surface of the ocean, measured on a scale 0-9, categorized by wave height.
sei whale
Balaenoptera borealis
seismic
relates to an earthquake, earth vibration or volcano
seismic reflection
a technique for examining the layers of the seafloor that uses the sound energy that is reflected by different layers in the seafloor.
seismic refraction
a technique for examining the layers of the seafloor that uses the sound energy that is refracted by different layers in the seafloor.
seismic wave
A wave of energy caused by the sudden movement of rock, as in an earthquake, or by an explosion. Seismic waves travel trough the Earth and are recorded by a seismometer.
seismometer
an instrument that records ground movement; used to detect and measure earthquakes
semi-terrestrial
living mostly on land but requiring water and/or a moist environment (esp. as a breeding site). Most amphibians (e.g. frogs) and many crustaceans (e.g. crabs) are semi-terrestrial.
sensorineural hearing loss
hearing loss due to damage to the nerves or inner ear structures
sensory hair cells
bundles of hair like projections (cilia) located on the surface of the inner ear that become stimulated by movement of the otolith against them. Stimulation of the hair cells results in sending a signal to the brain which is interpreted as sound.
setae
a stiff hair, bristle, or bristle like part on an organism.
shadow zone
a region of low sound intensity that sound waves traveling away from a source in the ocean do not reach, usually because the sound waves are refracted away from that region
shelf-edged habitats
ocean habitat on the edge of the continental shelf
shoal
a large school of fish
shock wave
A fully developed compression wave of large amplitude, across which density, pressure, and particle velocity change drastically.
side scan sonar
sonar is an acronym for sound navigation and ranging equipment. Sonar systems use sound waves to detect underwater objects by listening to the returning echoes. Side scan sonar uses the strength of the returning echo, not the travel time, to map the seafloor and identify objects on the seafloor.
signal
sound that is used for a specific task, such as to convey information.
signal excess
the amount (in decibels) by which the signal- to-noise ratio (SNR) exceeds the detection threshold (DT).
signal processing
analyzing sounds from a receiver to detect and classify sound sources
signal-to-noise (SNR) ratio
the ratio that compares the received level of a sound signal and the background noise level. For example, it is easy to hear conversations in a quiet room, where the signal-to-noise ratio is high, but it is difficult to hear conversations at a noisy party, where the signal-to-noise ratio is low.
signature sound
a unique sound that is associated with a specific sound source
signature whistle
tonal sounds produced by whales and dolphins that are unique to a particular individual and distinct from any other member of the group. Signature whistles provide a way to recognize individuals and help maintain group cohesion.
silver perch
Bairdiella chrysoura
sirenians
group of mammals that includes manatees and dugongs
snapping shrimp
Alpheus heterochaelis
SOFAR channel
SOFAR stands for SOund Fixing And Ranging. The sound speed minimum at 800-1000 meters of water depth is called the deep sound channel or, more historically, the SOFAR channel.
sonar
an acronym for SOund Navigation And Ranging equipment. Sonar systems use sound waves to detect underwater objects by listening to the returning echoes. The distance to the object or the seafloor can be calculated by measuring the time between when the signal is sent out and when the reflected sound, or echo, is received.
sonic muscle
a muscle that is attached to the swim bladder. Rapid flexure of the sonic muscle against the swim bladder produces drum-like sounds commonly associated with courtship and spawning behavior.
sonic muscle - swim bladder
a combined mechanism used by fishes to produce sound. The swim bladder is a gas filled organ primarily used for buoyancy control and is also important for hearing in some fishes. The sonic muscle is attached to the swim bladder. Rapid flexure of the sonic muscle against the swim bladder produces drum-like sounds commonly associated with courtship and spawning behavior.
soniferous
sound producing
sonobuoy
instrument that is dropped into the ocean (from either an aircraft or ship) to record underwater sounds. It includes a hydrophone and a radio transmitter to send sound signals back to the aircraft or ship. The U.S. Navy uses this instrument to listen for enemy submarines. Sonobuoys may also be used to record marine mammal calls and listen for earthquake activity.
sonogram
graphic presentation of a sound. A sonogram plots the frequency vs. time and represents the different intensity of the frequencies with different colors. It is similar to a contour map or bathymetric map where the different colors represent different water depths. Also called a spectrogram
sonoluminescence
the production of light as a result of the passing of sound waves through a liquid medium. The sound waves cause the formation of bubbles that emit bright flashes of light when they collapse.
sound channel
an area of slow sound speed that causes sound waves to become focused at this water depth
sound channel axis
depth of the minimum sound speed within the sound channel. Sound waves cycle above and below the axis as they move through the sound channel.
sound exposure level (SEL)
the decibel level of the time integral (summation) of the squared pressure over the duration of a sound event; units of dB re 1 µPa2-s
sound field
the level of sound at different distances and depths from the source
sound intensity level
10 times the logarithm of the ratio of the intensity of a sound wave to a reference intensity; also known as intensity.
sound level
10 times the logarithm of the ratio of the mean-square pressure of a sound to the square of a reference sound pressure. Sound pressure level will usually be shortened to sound level on the DOSITS website. Sound pressure level is given in relative units named decibels (dB). Sound pressures for transient signals are sometimes given as peak or peak-to-peak pressures, rather than mean-square pressure. To avoid ambiguity, the units for sound pressure level can be written dB rms for dB root-mean-square.
sound receptor
something that receives sound; sound receiver
sound source
something that creates sound
sound spreading loss
the decrease in intensity that occurs when a sound wave expands as it moves away from a source
Sound Surveillance System (SOSUS)
a network of hydrophones mounted on the seafloors of the North Atlantic and North Pacific oceans maintained by the US Navy
soundscape
The composite of all sounds in an environment. The perception of the soundscape for each animal will vary depending on its hearing abilities.
source level
the amount of sound radiated by a sound source. It is defined as the intensity of the radiated sound at a distance of 1 meter from the source, where intensity is the amount of sound power transmitted through a unit area in a specified direction. Source level is commonly given as a relative intensity in units named decibels (dB).
Southern California Offshore Range (SCORE)
a state-of-the-art facility that provides training and testing services to the U.S. Navy’s Pacific Fleet. The underwater tracking range is located west of San Clemente Island, CA, and consists of 84 bottom-mounted hydrophones that provide a coverage area of approximately 660 square nautical miles. Similar to AUTEC, a Marine Mammal Monitoring (M3R) system has been established at SCORE to monitor vocalizing animals via the bottom-mounted range hydrophones.
southern right whale
Eubalaena australis
Sparker
A sound source that uses an electric spark to generate a broadband signal.
spatulate
having a narrow base and a broad body (spade-shaped).
spawning
to produce, release, or deposit eggs for reproduction
spectrogram
a graphic presentation of a sound. A spectrogram plots the frequency vs. time and represents the different intensity of the frequencies with different colors. It is similar to a contour map or bathymetric map where the different colors represent different water depths. Also called a sonogram
sperm whale
Physeter macrocephalus
spermaceti organ
an elongated connective tissue sac in the forehead of the sperm whale that contains a waxy fluid called spermaceti
spherical spreading
energy spreading out from a sound source in the shape of a sphere; the power is radiated equally in all directions from the sound source
spinner dolphin
Stenella longirostris
sprat
Sprattus sprattus
spreading loss
a decrease in the intensity of a wave as it spreads out from a source
spy-hopping
a common whale activity in which they lift their heads above the surface of the water and observe what is happening on the surface. Whales will often spin around in order to observe in all directions.
squid
mollusks of the family Cephalopoda that are a favorite food of the sperm whale
standard deviation
an estimate of the variability of a set of measurements about the mean value; it is calculated by computing the square root of the variance.
standard deviation of the mean
an estimate of the variability of the mean value computed from a specific set of measurements; it is calculated by dividing the standard deviation of the measurements by the square root of the number of measurements; also often called the standard error of the mean.
static diffusion
when particles move from a region of higher concentration to a region of lower concentration
statistically significant
findings of an experiment or study that have a low probability of being due to chance alone
statistics
mathematical analysis that is used to explain and compare numerical data. This analysis helps make broader generalizations about a population from a smaller number of specific observations.
statocyst
a sac-like structure containing a mineralized mass (statolith) in association with numerous sensory cells.
stereo
short for stereophonic: a sound-reproduction system that uses two or more separate channels to give a more natural distribution of sound.
stereocilia
long, flexible hair-like structures that occur as a brush border on the surface of some membranes
stereociliary bundles
groups of hair-like projections on the upper surface of a hair cell. When stereocila bend, they trigger a release of chemicals that initiates the electrical signal (neural impulse) that is carried to and processed by the brain.
stereotyped
fixed or settled in form.
stewardship
the conducting, supervising, or managing of something, especially, the careful and responsible management of something entrusted to one's care.
stranding
an event where an aquatic animal, especially a marine mammal, lands on a beach or becomes stuck in shallow water, is dead or sometimes alive, and probably in distress.
streaked gurnards
Trigloporus lastoviza
streamers
a long (2000-6000 m) string of hydrophones typically used with air-gun arrays
stress response
the natural coping mechanism that allows the body to deal with stressful events. A group of physiological and behavioral processes enable an animal to adapt to changes in their environment.
stressor
anything that causes the body to respond by releasing stress hormones.
stridulate, stridulation
to produce a sound by rubbing two body parts together. Some fish make a shrill creaking noise by rubbing together bodily structures, especially skeletal parts.
striped dolphin
Stenella coeruleoalba
stripers
Morone saxatilis
subduction zones
places where two tectonic plates move toward each other, and one plate plunges beneath the other plate. Often ocean crust is subducting beneath continental crust
submarine canyon
narrow, steep-sided valleys on the sea floor.
subsonic
a frequency that is below the audible range
substrate
the surface or medium on which an organism lives or grows.
substratum (substrate)
the surface that an organism grows on or is attached to
supersaturated
more highly concentrated than is normally possible under given conditions of temperature and pressure
surf zone
The zone within which waves approaching the coastline start breaking; also called the breaker zone.
Surveillance Towed Array Sensor System (SURTASS)
a passive sonar system used to listen for noises produced by submarines. The system consists of a long string of underwater hydrophones that are towed behind a ship and pick up sounds in the ocean.
SUS (Signal, Underwater Sound)
an explosive sound source used by the U.S. Navy that consists of 0.82-kg (1.8-lb) of TNT explosive material.
swim bladder
a gas filled organ that is primarily used for buoyancy control but is also important for hearing in some fishes.
swim bladder (also called an air bladder)
an expandable, gas-filled sac that helps fish maintain buoyancy in the water. This organ is also important for hearing in some species of fish.
synapse
a junction between a nerve cell and another nerve cell or a nerve fiber or a sensory receptor

T

t-test
a statistic that compares the sample means with the standard deviations of the sample means to determine whether the two sample means are statistically different.
target strength
the amount of sound reflected back toward a sonar by a target.
tectonic
relating to the deformation of the earth's crust
tectorial membrane
a membrane that covers the surface of the organ of Corti in the cochlea of the inner ear
telemetry
measuring and transmitting data from a remote location
temperature
a measure of the atomic and molecular vibration in a substance, in degrees. The response of a solid, liquid, or gas to the input or removal of heat energy.
temporary threshold shift (TTS)
a temporary increase in the threshold of hearing (minimum intensity needed to hear a sound) at a specific frequency that returns to its pre-exposure level over time
terrestrial
something that lives on land as opposed to in the water. Some animals, such as sea lions spend time both on land and in the water, they are considered to be both terrestrial and marine.
territoriality/territorial
behavior in which an organism, for example a fish, defends its home
Tertiary wave
seismic energy that has been converted into acoustic energy in the ocean. Also known as a "T-wave".
test
the outer skeleton of a sea urchin. It is made up of plates that encircle the sea urchin. Spines of the sea urchin grow from the test.
Thalassia
a broad-bladed seagrass occurring in shallow tropical and subtropical estuaries and nearshore marine waters
theory
a hypothesis or group of hypotheses that have been consistently validated through scientific observations or experiments. Geology's theory of plate tectonics is an example of a well-documented and widely accepted theory.
thermocline
a layer of water in an ocean or certain lakes, that separates warmer surface water from colder deep water. Temperature rapidly changes with depth in this region of the water column.
thermometry
the measurement of temperature
threshold of hearing
the minimum intensity where a person with normal hearing can hear a sound. The intensity level varies with frequency. Lower frequency sounds generally have a much higher threshold of hearing. It ranges from 0 to 75 dB depending on the frequency.
threshold of pain
the intensity level where sound is physically painful. Usually at 115-130 dB.
threshold shift
an increase (worsening) in the threshold of hearing for an ear at a specified frequency
tiger shark
Galeocerdo cuvier
TNT
trinitrotoluene; a chemical compound used as an explosive material.
toadfish
opsanus tau
towfish
an instrument, such as a side scan sonar, that is towed behind a ship
trachea
a large membranous tube reinforced by rings of cartilage, extending from the larynx to the bronchial tubes and conveying air to and from the lungs; the windpipe.
transducer
the part of the sonar system that functions like an antenna, sending out sonar signals (sound waves) and receiving return echoes. The transducer converts electrical energy into sound waves and vice versa.
transmission loss
the decrease in acoustic intensity (due to spreading and/or attenuation) as an underwater sound wave propagates outwards from a source.
transmitter
an instrument that sends out slectrical signals
transponder
an acoustic signaling device that automatically transmits a sonar signal upon reception of a designated incoming signal. Transponders are used to mark or track underwater objects.
transverse wave
a disturbance in which the particles vibrate up-and-down and the energy moves left-and-right
trill
a fluttering sound that alternates rapidly with another note
tsunami
A tsunami is a series of ocean waves generated by sudden displacements in the sea floor, landslides, or volcanic activity. In the deep ocean, the tsunami wave may only be a few inches high at the sea surface. When a tsunami wave comes ashore it will increase in height and can become a fast moving wall of water several meters high.
tubercle
a small rounded projection.
tuned airgun array
multiple airguns of different, carefully selected volumes that are fired at the same time.
tympanic membrane or eardrum
a membrane that separates the outer ear from the middle ear. The eardrum vibrates in response to sound waves and passes the vibrations on to the bones of the middle ear.
Type I Error
an error when one concludes that there is a real difference between two means when, in fact, there is not; also called a false positive error.
Type II Error
an error when one concludes that there is not a real difference between two means when, in fact, there is a difference; also called a false negative error.

U

ultrasonic
sound waves that have a frequency that is higher than what humans can hear (i.e. greater than 20,000 Hz). Bats and dolphins use these high frequency sounds for communication and navigation.
ultrasound signal
sound vibrations that have frequencies above the range of human hearing
underwater dB
the relative unit used to specify the intensity of an underwater sound. The phrase underwater dB is used on DOSITS to indicate decibels computed using root-mean-square (rms) pressure unless otherwise indicated. Underwater dB are referenced to a pressure of 1 microPascal (µPa), which is abbreviated as dB re 1 µPa. To be able to compare relative intensities given in dB to one another, a standard reference intensity or reference pressure must always be used. Scientists have agreed to use 1 microPascal (µPa) as the reference pressure for underwater sound. In air, however, scientists have agreed to use a higher reference pressure of 20 microPascals. It is important to remember that sound intensity given in underwater dB is not the same as sound intensity given in air dB. See the Advanced Topics Introduction to Decibels and Introduction to Signal Levels for additional information.

V

vacuum
a space from which all gas and other matter has been removed
vaquita
Phocoena sinus
variance
an estimate of the variability of a set of measurements about the mean value; it is calculated by subtracting the mean from each of the measurements, squaring the differences, adding all of the squared differences together, and dividing by one less than the total number of measurements; the square root of the variance is the standard deviation.
vector
a quantity, such as a velocity or force, that has both magnitude and direction.
velocity
the linear speed of an object in a specified direction.
ventral
of, pertaining to, or situated at the back or upper side.
vertebrate
having vertebrae or having a backbone or spinal column. Fish and humans are examples of vertebrates.
vertical migration
a pattern of movement that some marine organisms undertake each day. Usually organisms move to shallow waters at night and return to deeper waters during the day.
vestibular system
a fluid-filled maze of canals and chambers inside the inner ear that helps maintain orientation and balance.
viscosity
a molecule's resistance to motion
vital rates
relative frequencies of vital occurrences that affect changes in the size and composition of a population, such as birth rate or death rate
vocal cords
Small bands of tissue within the larynx that vibrate (when air passes over them) to produce the sound.
vocal fold ligament
connective tissue that strengthens the vocal folds via stiffness and support
vocal learning
the modification of an animal’s vocalization(s) based on acoustic signals in its environment, such as vocalizations by conspecifics.
vocalizations
sounds intentionally produced by animals that may be used for communication, navigation, and feeding. In humans, air is moved from the lungs and across the vocal folds (also known as vocal cords). The vibration of the vocal folds produce sounds that are formed into words and other vocal communication signals. We do not know how sound is produced by many species of marine mammals. The term vocalization is commonly used to refer to sounds that are produced by marine mammals; however, the use of the word vocalization does not imply that marine animals are using vocal folds to produce the sounds.
vulnerable
susceptible to being hurt or damaged.

W

walleye pollock
Theragra chalcogramma
walrus
Odobenus rosmarus
wave
disturbance caused by the movement of energy through a medium
wave front
a surface consisting of all points on a wave at the same position in a wave cycle.
waveform
A waveform presents the sound in a graph as positive and negative pressure on a relative scale (often from -1 to 1) through time. The relative pressure is related to the intensity of the sound.
wavelength
the length of one cycle of a wave (one crest and one trough)
Weberian ossicles
a series of bones which connect the swim bladder to the inner ear and carry vibrations between to the two, aiding in hearing.
weddell seal
Leptonychotes weddelli
whistles
narrow-band, tonal sounds produced by many toothed whales for communication purposes. Whistles are frequency-modulated, which means the pitch of the sound changes over time.
white noise
a heterogeneous mixture of sound waves extending over a wide frequency range (but equal intensities).
white-beaked dolphin
Lagenorhynchus albirostris
white-sided dolphin
Lagenorhynchus spp.

Y

Yangtze finless porpoise
Neophocaena phocaenoides
yellowtail rockfish
Sebastes flavidus

Z

zooplankton
Microscopic animals, such as crustaceans and fish larvae, that drift in the water column.