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7.0 GLOSSARY

95% Exposure Range: The horizontal range that includes 95 percent of animat (simulated animal) closest 

points of approach (CPAs) that exceed a given impact threshold.

Abiotic: Non-living part of the ecosystem such as air, water, and substrates. 

Accuracy: The degree to which measurements or models reflect the actual value or condition of the 

subject being measured or characterized.

Acoustic Impedance: Ratio of sound pressure to sound volume. 

Action Area: The geographic location where the NOS Proposed Action would occur. It includes rivers, 

states’ offshore waters, the United States (U.S.) territorial sea, the contiguous zone, U.S. portions of 

the Great Lakes, the U.S. Exclusive Economic Zone, and coastal and riparian lands.

Active Sonar: A type of Sound Navigation and Ranging (sonar) that detects objects by creating a sound 

pulse that is transmitted through the water, reflects off a target object, and returns in the form of an 

echo to be detected.

Additive Cumulative Effect: An impact on a resource which is the sum of the individual impacts on that 

resource.

Adverse Impacts: Effects which are negative and harmful for the analyzed resource; and cause a change 

that moves the resource away from a desired condition or detracts from its appearance or condition.

Algal Flat: An assemblage of cyanobacteria (i.e., blue-green algae) or other photosynthetic 

microorganisms forming a dense flat mass, especially on or within the surface layer of an aquatic 

sediment.

Alkali Flat: Dried-out lake beds adjacent to coasts containing high salt concentrations.

Alkali lake: A saline water body containing large amounts of sodium and potassium carbonates in solution 

as well as sodium chloride, commonly found in arid regions.

Amphipod: An order of crustaceans, resembling shrimp, with no carapace (i.e., hard upper shell) and 

ranging from 1 to 340 millimeters (mm) in length, comprising both marine and freshwater forms. 

Amphipods are detritivores (i.e., feed on dead organic material) or scavengers.

Amplitude: Magnitude of the largest departure from its equilibrium value of an acoustic variable. High 

amplitude corresponds to high intensity.

Anadromous: A general category of fish, such as the salmon, which hatch in fresh water, spend most of 

their lives in the salt water of the ocean, and then return to fresh water to spawn.

Angling: Recreational fishing with hook and line.

Animat: Computer simulated animals used in behavioral research and modeling. 

Annelid: Macroinvertebrate phylum consisting of segmented worms, including polychaetes (e.g., bristle 

worms).

Aquaculture: The artificial breeding, rearing, and harvesting of fish, shellfish, plants, algae, and other 

organisms in all types of water environments.

Aquatic Macroinvertebrate: Small organisms that have no internal skeletal system and live part or all of 

their lives in water; they are visible without the aid of a microscope.
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Archipelago: Area that contains a chain or group of islands scattered in lakes, rivers, or the ocean. 

Area of Potential Effect (APE): The geographic location within which a physical undertaking may directly 

or indirectly cause alterations in the character or use of historic properties, if any such properties 

exist. The APE is influenced by the scale and nature of an undertaking and may be different for 

different kinds of effects caused by the undertaking.

Arribada: The synchronized, large-scale nesting on sandy beaches of some species of sea turtle (e.g., 

Kemp's ridley and olive ridley).

Arthropod: Phylum consisting of macroinvertebrate animals with exoskeletons, including (in marine 

habitats) crustaceans such as lobsters, crabs, shrimp, as well as amphipods, barnacles, and copepods.

Astrolabe: A historic scientific instrument used for reckoning time and for observational purposes.

Atoll: A ring-shaped coral reef, island, or series of islets.

Audiogram: A chart that shows the results of a hearing test.

Auditory Masking: The reduction in an animal’s ability to perceive, recognize, or decode biologically 

relevant sounds because of interfering sounds.

Automatic Identification System (AIS): A shipboard broadcast system that acts like a transponder and 

uniquely identifies ships and vessels, using radio or satellite transceivers. 

A-weighting Function: A mathematical curve that takes into account the average sensitivity of the human 

ear to sound frequency. A-weighting is used to convert a physical quantity of acoustic pressure (in 

decibels [dB]) to a value that better quantifies how loud a noise is perceived by humans. Corresponds 

to M-weighting functions for marine mammals.

Back-reef Habitat: Shallow lagoon between a barrier reef and the shoreline, often including small patches 

of corals, sand plains, and seagrass beds; waters in this habitat are typically warmer than outside the 

reef because of shallow depth, reduced water circulation, and shelter from wave action. Salinity may 

fluctuate because of variable freshwater inflow. 

Backscatter: The scattering of particles or radiation, such as sound waves, by the atoms of the medium 

through which they pass, in the backward direction. 

Bait Cup (also known as grinding hole): Small depressions ground into bedrock.

Baleen: The apparatus inside the mouths of toothless whales, upon which they rely to filter food from the 

sea.

Ballast Water: Fresh or salt water, sometimes containing sediments, held in tanks and cargo holds of ships 

to increase stability and maneuverability during transit. 

Bank Reef: Reef that is built upward from the seafloor by non-photosynthetic coral.

Barotrauma: Injury from excessive water pressure.

Barrier Reef: A coral reef roughly parallel to a shore and separated from it by a lagoon or channel of deep 

water.

Bathymetry: The depths and shapes of underwater terrain, or submarine topography.

Bathypelagic: Zone of the open ocean that extends from a depth of 1,000 to 4,000 meters (m) beneath 

the surface, with little or no sunlight present in the ecosystem. Above lies the mesopelagic zone; 

below the abyssopelagic zone. 
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Beach Nourishment: Process by which sediment, usually sand, lost through longshore drift or erosion is 

artificially replaced with sediment from other sources.

Beneficial Impacts: Effects which are positive and supportive for the analyzed resource. A beneficial 

impact constitutes a positive change in the condition or appearance of the resource or a change that 

moves the resource toward a desired condition.

Benthic: Relating to or occurring at the bottom of a body of water or in the depths of the ocean.

Benthos: The flora and fauna found on the bottom, or in the bottom sediments, of a sea, lake, or other 

body of water.

Best Management Practice (BMP): An action or a combination of actions, that is determined to be an 

effective and practicable means of preventing or reducing adverse impacts to a resource. 

Bicarbonate: A salt of carbonic acid containing the ion HCO3

–

.

Bilge: Area on the outer surface of a ship's hull where the bottom curves to meet the vertical sides. The 

bilge of a ship or boat is the part of the hull that would rest on the ground if the vessel were 

unsupported by water.

Bilge Water: Water that is generated by various activities involved in keeping a ship running while at sea. 

It collects in the hull of a vessel and contains industrial fluids from machinery spaces, internal drainage 

systems, sludge tanks, and various other sources.

Bioaccumulation: Over time, the buildup of ingested substances, typically heavy metals, pesticides, or 

toxins, in the tissues of a living organism. This occurs when an organism absorbs a substance at a rate 

faster than that at which the substance is lost or eliminated.

Biodiversity: The variety and variability of life on Earth. Biodiversity is typically a measure of variation at 

the genetic, species, and ecosystem level. Terrestrial biodiversity is usually greater near the equator, 

which is the result of the warm climate and high primary productivity, and lower in polar regions.

Biologically Important Area (BIA): Spatially defined locations where aggregations of individuals of 

cetaceans display biologically important behaviors which are region-, species-, and time-specific.

Bioluminescence: Light produced by a chemical reaction within a living organism; occurs widely in marine 

vertebrates and invertebrates.

Biosphere: Layer of the Earth where life exists.

Biotic: Relating to or resulting from living things, especially in their ecological relations.

Bivalve: Aquatic mollusk with two hinged shells, such as oysters, clams, mussels, and scallops.

Bleaching (of coral): Under conditions of thermal stress, the process of expelling the algae (zooxanthellae) 

living in the tissues of coral polyps, causing the corals to turn completely white; bleaching for an 

extended period of time can lead to mortality of the coral polyps and hence the coral reef. 

Blubber: The thick layer of fat under the skin of marine mammals, such as seals, whales, and walruses.

Bluff: Steep shoreline slope formed in sediment (i.e., loose material such as clay, sand, and gravel) that 

has three feet or more of vertical elevation just above the high tide line.

Brachiopod: Phylum consisting of marine macroinvertebrates with hard “valves” or shells on their upper 

and lower surfaces.

Brackish: Water with salinity levels higher than fresh water but lower than sea water (salt water).
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Breaching (for whales): Leaping above the water. 

Broadband: Data transmission using a wide range of frequencies. 

Broadband Sound: Vibrations with a combination of many frequencies distributed over a wide section of 

the audible range; as opposed to narrowband sound.

Bryozoan: Macroinvertebrate phylum consisting of moss animals or sea mats.

Bycatch: Fish or shellfish caught unintentionally or inadvertently while pursuing other target species.

Capital: Human-created assets that can enhance one's power to perform economically useful work.

Carbon Geosequestration: Depositing and storing carbon in a reservoir beneath the Earth’s surface.

Catadromous: A general category describing fish, such as eels, that live in fresh water and migrate to salt 

water to spawn.

Cavitation: A phenomenon in which rapid changes of pressure in a liquid lead to the formation of small 

vapor-filled cavities (i.e., bubbles) in places where the pressure is relatively low.

Cephalopod: Active predatory mollusk of the large class Cephalopoda, such as an octopus or squid.

Cetacean: Completely aquatic marine mammals such as whales, dolphins, and porpoises; they feed, mate, 

calve, and suckle their young in the water.

Chartered Vessel: Vessels that are owned and/or operated by a private firm and are operating under an 

NOS contract. 

Cilia: Microscopic hair-like structures on the surface of certain cells that either cause currents in the 

surrounding fluid, or, in some protozoans and other small organisms, provide propulsion.

Closest Point of Approach (CPA): Term used in modeling the level of sound exposure of marine mammals 

to an underwater sound source; refers to the closest horizontal distance of animats from a sound 

source.

Cnidaria: Phylum of macroinvertebrate marine fauna including jellyfish, sea anemones, and corals.

Coastal Birds: Birds which occupy coastal habitats, such as shorebirds, pelicans, terns, gulls, and some 

waterfowl and wading birds. 

Community: Group or association of populations of two or more different species occupying the same 

ecosystem.

Conservative Estimate: Use of assumptions in analysis methodologies that result in larger impacts on the 

environment. 

Conspecific: Animals or plants belonging to the same species. 

Consumer Surplus: The value of goods in excess of the costs of acquisition.

Contiguous Zone: A band of water extending farther from the outer edge of the territorial sea to up to 24 

nautical miles (nm) (44.4 kilometers [km]) from the baseline. The zone established by the United 

States under Article 24 of the Convention on the Territorial Sea and the Contiguous Zone, as published 

in the June 1, 1972 issue of the Federal Register.

Continental Shelf: The area of sea bed around a large landmass where the sea is relatively shallow 

compared with the open ocean.
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Continental Slope: The deepening sea floor out from the continental shelf (see definition above) edge to 

the upper limit of the continental rise, or the point where there is a general decrease in steepness.

Continuous Sound: Vibration that is present at all times in a relevant time window.

Copepod: Small aquatic crustaceans that are one of the most numerous macroinvertebrates in aquatic 

communities. They inhabit a wide range of salinities, from fresh water to hypersaline conditions.

Coral Polyps: Sessile macroinvertebrates of the class Anthoza that typically form and live in large colonies 

known as coral reefs, which constitute some of the most biodiverse communities on Earth.

Corallite: Skeleton of an individual coral polyp.

Core: Samples that preserve surface and subsurface sediment layers. 

Countervailing Cumulative Effect: Where the net adverse impact is less than the sum of the individual 

impacts.

Critical Habitat: Specific geographic area, as formally designated by the U.S. Fish and Wildlife Service or 

National Marine Fisheries Service under the Endangered Species Act (ESA), that contains features 

essential to the conservation of an endangered or threatened species and that may require special 

management and protection. May also include areas that are not currently occupied by the species

but will be needed for its recovery.

Cryopelagic: Relating to the underside of an oceanic ice layer or the water immediately below the ice 

surface. 

Cultural Landscape: A geographic area, including both cultural and natural resources and the wildlife or 

domestic animals therein, associated with a historic event, activity, or person, or exhibiting other 

cultural or aesthetic values.

Cumulative Actions: Past, present, and reasonably foreseeable future activities that are addressed in the 

cumulative effects analysis because their environmental effects may combine or interact with the 

effects of the Proposed Action.

Cumulative Impacts: Effects on the environment from the incremental effect of the Proposed Action 

when added to other past, present, and reasonably foreseeable future actions.

Cumulative Sound Exposure Level (SEL): A measure of energy that takes into account both received level 

and duration of exposure; total combined sound energy to which an animal has been exposed over 

time. 

Datum: A coordinate system and a set of reference points used for locating places on the Earth. Datums 

are used in navigation and surveying by cartographers, surveyors, and navigation systems to translate 

positions indicated on maps to their real position on Earth.

De minimis: Referring to environmental impacts so minimal as to merit disregard.

De-ballast: Exchange of ballast water (see definition above) in open ocean waters (for vessels that have 

ballast tanks).

Decidecade Band: A logarithmic frequency interval equal to one tenth of a decade (i.e., a unit for 

measuring ratios on a logarithmic scale, with one decade corresponding to a ratio of 10 between two 

numbers); it is approximately equal to one third of an octave.

Delphinid: Oceanic dolphin belonging to the family Delphinidae. 
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Demand: The desire of purchasers, consumers, clients, employers, etc., for a particular commodity, 

service, or other item.

Demersal: Relating to or near the ocean bottom, typically in reference to fish species such as cod, 

haddock, and flatfish (e.g., halibut) that live on or near the sea floor.

Deoxygenation: A decrease in dissolved oxygen concentration in fresh or saltwater habitats.

Depleted (under the MMPA): Status of a species under the Marine Mammal Protection Act (MMPA) when 

its population falls below the optimum sustainable population level. 

Depredation: The act of preying upon, such as the killing of adult birds and offspring by natural predators.

Designed Cultural Landscape: A setting that includes purposefully planned views or vistas.

Detritus: In aquatic ecosystems, refers to dead particulate organic material, as opposed to dissolved 

organic material. It usually includes the remains or fragments of dead organisms as well as fecal 

material, and often hosts communities of microorganisms that both colonize and decompose it.

Diadromous: A general category describing fish that spend portions of their life cycles partially in fresh 

water and partially in salt water, including both anadromous and catadromous fish. 

Direct effect: Impact caused by an action that occurs at the same time and place.

Distinct Population Segment (DPS): A vertebrate population (i.e., a group of potentially interbreeding 

organisms in the same species in a given locality) or group of populations that is discrete from other 

populations of the species and significant in relation to the entire species.

Doppler Shift: Relative change in the frequency of sounds emitted by approaching or receding sound 

sources.

Downwelling: A process where surface water is forced downwards, where it may deliver oxygen to deeper 

waters, increasing dissolved oxygen concentrations in the depths. 

Dredge: Remove sediment from the sea bed, lake bed, river bed, or the bottom of artificial waterways, 

typically done to increase or restore water depth for the transit of vessels or to restore the volume of 

water in lakes filling in with sediments.

Duty Cycle: The fraction or percentage of time that a source is ‘on’ in a relevant time window (e.g., a 

source transmitting for two hours per day has a duty cycle of 2/24 = 0.08 = 8 percent).

Echinoderm: Member of a phylum of marine macroinvertebrates; the adults are recognizable by their 

radial symmetry, including sea stars, sea urchins, sea cucumbers, sand dollars, and crinoids.

Echolocation: The use of sound waves and echoes to determine where objects are in space, used both in 

air (by bats) and water (by marine mammals).

Economic Sector: Components of the economy which are distinct from each other. 

Ecosystem: A system of biotic (i.e., living) and abiotic (i.e., non-living) components that interact with each 

other and function together as a unit.

Effects Determination: Process employed under the ESA to formally conclude whether actions may affect 

listed species or designated critical habitat.

Electric Load Planning: The process of forecasting the demand for electricity of a community and adjusting 

the generation and transmission of electricity accordingly. 
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Electrophysiological Studies: Investigations which stimulate the flow of ions into tissue in order to deduce 

the functional capabilities of anatomical structures. 

Endangered: A species is considered endangered under the ESA if it is in danger of extinction throughout 

all or a significant portion of its range.

Endemic: Native and restricted to a certain place, often referring to a species confined to a given locale.

Energy Source Level: In acoustics, 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 given as a relative intensity measured in decibels.

Ensonify: To fill with sound, for example, a given volume of water of a given shape and configuration. 

Environmental Justice: A condition under which no population bears a disproportionate share of negative 

environmental consequences resulting from industrial, municipal, and commercial operations or from 

the execution of federal, state, and local services, laws, regulations, and policies.

Epipelagic: The part of the ocean where there is enough sunlight for algae to utilize photosynthesis; this 

zone reaches from the sea surface down to approximately 200 m (650 feet).

Episodic Erosion: The shore and backshore adjustment that results from short-duration, high-intensity 

meteorologic and oceanic storm events. This type of event response results in shore adjustment and 

occurs during a single storm or during a series of closely spaced storm events within a storm season.

Escarpment: An area of ground surface at which elevation changes suddenly. It usually refers to a cliff, 

precipice, or steep slope.

Essential Fish Habitat: Those waters and substrate necessary for fish for spawning, breeding, feeding, or 

growth to maturity, as designated by the National Marine Fisheries Service.

Eutrophication: Excessive richness of nutrients (e.g., nitrates and phosphates) in a lake or other body of 

water, frequently due to runoff from the land, which causes a dense growth of plant life (e.g., algal 

blooms) and death of aquatic animal life from lack of oxygen when the algae die en masse and 

decompose.

Evolutionarily Significant Unit (ESU): A population of organisms considered distinct for the purposes of 

conservation action; may be a species, subspecies, race, population, or stock, such as a stock of salmon 

associated with a particular river.

Exclusive Economic Zone (EEZ): Area of the sea where the U.S. and other coastal nations have jurisdiction 

over natural resources. The U.S. EEZ extends no more than 200 nautical miles from the territorial sea 

baseline and is adjacent to the 12 nautical mile territorial sea of the U.S., including the Commonwealth 

of Puerto Rico, Guam, American Samoa, the U.S. Virgin Islands, the Commonwealth of the Northern 

Mariana Islands, and any other territory or possession over which the United States exercises 

sovereignty.

Exoskeleton: A rigid, external supportive covering of an animal, such as an arthropod.

Federal Subsistence Priority: Subsistence (see definition below) uses by rural residents of Alaska are 

accorded priority by the federal government over non-subsistence uses, commercial or sport.

Federally Recognized Tribes: An American Indian or Alaska Native tribal entity that is recognized as having 

a government-to-government relationship with the U.S., with the responsibilities, powers, limitations, 

and obligations attached to that designation, and is eligible for funding and services from the Bureau 
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of Indian Affairs. See 86 FR 7554, updated by 86 FR 18552, for the full list of 574 federally recognized 

tribes.

Feeding Area: Areas and months within which a particular species or population selectively eats. These 

may either be found consistently in space and time, or may be associated with ephemeral features 

that are less predictable but can be delineated and are generally located within a larger identifiable 

area.

Filter Feeder: Animals that eat by moving water through a structure that acts as a sieve, straining 

suspended matter and food particles or prey from the water.

Fissiped: Members of the taxonomic order Carnivora, having toes separated to the base, including sea 

otters and polar bears. 

Fishery Management Councils (FMC): Eight regional bodies composed of knowledgeable people with a 

stake in fishery management, established under the Magnuson-Stevens Fishery Conservation and 

Management Act, to develop regional Fishery Management Plans and responsibly manage fish and 

shellfish species in waters within the U.S. EEZ. 

Fishing Community: A social or economic group whose members reside in a specific location and share a 

common dependency on commercial, recreational, or subsistence fishing or on directly related 

fisheries dependent services and industries (e.g., boatyards, ice suppliers, tackle shops). 

Fishing Lure: Artificial fishing bait designed to attract a fish's attention and instigate a bite so as to impale 

the fish on a hook; one or more hooks are often hidden within the lure.

Fjord: A long, deep, narrow body of water that reaches far inland and is bordered by steep mountains; in 

the continental United States, they are found only in Alaska.

Fledging Period: The stage in a flying animal's life between hatching or birth and becoming capable of 

flight.

Fledgling: A young bird which has developed wing feathers that are large and strong enough for flight.

Floe: A layer of floating ice on the surface of a water body; distinct from icebergs, which have calved from 

tidewater glaciers and have more vertical structure.

Flume: A narrow channel conveying water.

Fore Reef: The outside part of a reef (see definition below) seaward of the reef edge facing the open sea.

Fourier Transform: Algorithm that decomposes functions depending on space or time into functions 

depending on spatial or temporal frequency. Used to compute the spectral (frequency) content of a 

signal.

Frequency: Rate of oscillation of a sound wave as the number of cycles per second: ff [unit is Hz: Hertz]; 1 

HHz = 1/ss [second]; higher-frequency sounds are perceived as higher-pitched to the observer. Animal 

species are able to perceive sounds within given frequency ranges that vary from species to species. 

Sounds below or above that frequency range cannot be heard or detected by that species. 

Fringing Reef: One of the three main types of coral reef (see definition below). It is distinguished from the 

other main types, barrier reefs and atolls, in that it has either an entirely shallow backreef zone (i.e., 

lagoon) or none at all. Grows seaward directly from the shore and forms a border along the shoreline 

and surrounding islands. 

Frontal Zone: The transition area, sometimes amounting to a discontinuity, that separates adjacent air 

masses.
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Fusiform: Tapering at both ends; spindle-shaped.

Gastropod: Mollusks of the class Gastropoda, having a head with eyes and feelers and a muscular foot on 

the underside of its body with which it moves. Most gastropods are aquatic in both fresh and salt 

water, but some have evolved to live on land, such as some snails and slugs; may have a univalve shell 

or none.

Geological and Geophysical (G&G) Surveys: Conducted to obtain data for oil and gas exploration and 

production; uses high-intensity active acoustic sources that penetrate the surface of the sea floor.

Gill Net: A fishing mesh which is hung vertically so that fish get trapped in it by their gills (i.e., the 

respiratory organs of fish).

Gross Domestic Product (GDP): The total value of goods produced and services provided in a country 

during one year.

Ground Truthing: To directly confirm, or validate by direct observation, information or data that was 

derived indirectly. 

Gyre: A large system of rotating ocean currents. 

Habitat: The natural environment of an organism; a place possessing the features and resources needed 

to promote the life and growth of an organism or a species.

Habitat Areas of Particular Concern (HAPC): A designation that encompasses discrete subsets of Essential 

Fish Habitat; high-priority locales for conservation, management, or research because they are rare, 

sensitive, stressed by development, or important to ecosystem function.

Habitat Occupancy: The presence of a given species within a habitat area.

Hard Bottom: Refers to exposed rock underneath a waterbody but includes other substrata such as coral 

and artificial structures.

Hatchling: A young bird that has recently emerged from its egg and is typically still nest-bound.

Haul Out: To come out of the water to spend time on land; practiced in particular by certain pinnipeds.

Head-of-tide: The inland limit of water affected by the rise and fall of sea levels.

Headwaters: The inland source from which a river originates within a basin or watershed; often refers to 

adjacent lands as well as waters within the upper reaches of a river basin.

Hearing Threshold: The minimum sound level, measured in decibels that an animal can hear within a 

specified frequency band.

Hearing Threshold Shifts: Changes in the hearing range of an organism due to exposure to high intensity 

sounds.

Highly Migratory Species (HMS): Fish that travel long distances and often cross domestic and 

international boundaries. These pelagic fish live in the open ocean, although they may spend part of 

their life cycle in nearshore waters.

High Resolution Geophysical (HRG) Survey: A type of geological and geophysical survey that uses sound 

waves that are reflected off submerged structures to collect data on conditions both at the sea floor 

and the shallow subsurface. 

High Tide Line: The intersection of the land with the water's surface at the maximum height reached by a 

rising tide.
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Historic Property: Any prehistoric or historic district, site, building, structure, or object included in, or 

eligible for inclusion in, the National Register of Historic Places maintained by the Secretory of the 

Interior. This term includes artifacts, records, and remains that are related to and located within such 

properties and also includes properties of traditional religious and cultural importance to an Indian 

tribe or Hawaiian organization and that meet the National Register criteria. 

Homing Propensity: Tendency to return to the locations where a species originated.

Hydrocarbon: A compound of hydrogen and carbon, such as any of those which are the chief components 

of coal, petroleum, and natural gas (i.e., the fossil fuels).

Hydrography: The measurement and description of the physical features of oceans, seas, coastal areas, 

lakes, and rivers, as well as the prediction of their change over time, for the primary purpose of safety 

of navigation and in support of all other marine activities.

Hypoxia: Refers to low or depleted dissolved oxygen in a body of water. 

Ice Seals: Four species of seals found in the Arctic – bearded, ringed, spotted, and ribbon – which are 

collectively called ice seals because of their association with sea ice for feeding, resting, and pupping.

Illegal, Unreported, and Unregulated (IUU) Fishing: Fishing activities that violate both national and 

international fishing regulations. 

Immunocompetency or Immunocompetence: The ability of the body or of an organism to respond to 

illness.

Impulsive Sound: Sounds that are typically transient, brief (less than 1 second), broadband, and consist 

of high peak sound pressure (i.e., the decibel level of the maximum instantaneous acoustic pressure 

in a stated frequency band) with rapid rise time and rapid decay.

Indirect Effect: Environmental impact that is caused by the action and occurs later in time or is farther 

removed in distance but is still reasonably foreseeable. Indirect effects also include “induced changes” 

in the human and natural environments.

Insolation: Sunlight or incoming solar radiation. 

Intermittent Sound: A sound that is periodically present, in contrast to one that is constant or continuous.

Intertidal Zone: Area where the ocean meets the land between high and low tides. 

Inverse Fourier Transform: A mathematical algorithm that converts a space or time signal to a signal of 

the frequency domain; converting spatial or temporal data into the frequency domain data. It

computes the time-domain signal, h(t), from the spectral components H(t).

Invertebrate: Animal lacking a backbone.

Irretrievable Impact: Losses to or effects on natural resources that are lost for a period of time, but not 

permanently.

Irreversible Impact: Losses to or effects on natural resources from use or depletion of nonrenewable 

resources, such as fossil fuels or cultural resources, or to factors such as soil productivity that are 

renewable only over long periods of time.

Isopleth: Lines or curves on a map of equal values; contour lines on a topographic map depicting ground 

surfaces of the same elevation are an example of isopleths.

Karigi: Special houses used for performing ritual ceremonies by Alaska Natives.
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Knot (unit): A unit of speed equal to one nautical mile per hour, exactly 1.852 kilometers per hour (km/h) 

(approximately 1.15078 miles per hour [mph] or 0.514 meters per second [m/s]).

Krill: Small, planktonic, shrimp-like crustaceans of the open oceans that are eaten by a number of marine 

animals, notably the baleen whales; they have been described as “essentially the fuel that runs the 

engine of the Earth’s marine ecosystems.”

Lagoon: A shallow body of water that may have an opening to a larger body of water but is also protected 

from it by a sandbar or coral reef; often brackish when near the sea.

Launch: A small boat that is deployed into the water directly from a ship. 

Lentic: Inhabiting or situated in still fresh water, such as the waters of a lake. 

Level A Harassment: Any act of pursuit, torment, or annoyance which has the potential to injure a marine 

mammal or marine mammal stock in the wild. 

Level B Harassment: Any act of pursuit, torment or annoyance which has the potential to disturb a marine 

mammal or marine mammal stock in the wild by causing a disruption of behavioral patterns, including, 

but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering but which does not 

have the potential to injure a marine mammal or marine mammal stock in the wild.

Lidar: Acronym for Light Detection And Ranging. A remote sensing technology that uses light in the form 

of a pulsed laser to measure ranges (i.e., distances) to a target.

Liquefied Natural Gas (LNG): A form of natural gas (i.e., a naturally occurring hydrocarbon gas mixture 

consisting primarily of methane) that has been cooled down so that it has a reduced volume and 

behaves as a liquid.

Lithic: Of the nature of or relating to stone; in archaeology, it refers to any stone that has been used or 

beat on by humans. 

Lombard Effect: A phenomenon in which speakers increase their vocal production to communicate in 

noisy environments.

Low-income Population: Group of individuals living in geographic proximity to one another, or a 

geographically dispersed or transient (i.e., migrant) group of individuals that have household incomes 

at or below the designated “low-income” threshold or the designated federal poverty level. 

Macroalgae: Large marine algae, often living attached in dense beds, such as kelp and seaweed.

Macrohabitat: An extensive habitat presenting considerable variation of the environment, containing a 

variety of ecological niches, and supporting a large number and variety of complex flora and fauna. 

Macroinvertebrate: An animal lacking a backbone that can be seen without the aid of a microscope and 

captured by a 500--micrometer (μm) net or sieve. This includes arthropods (e.g., insects, mites, scuds 

and crayfish), mollusks (e.g., snails, limpets, mussels and clams), annelids (e.g., segmented worms), 

nematodes (e.g., roundworms), and platyhelminthes (e.g., flatworms).

Mangrove: A tree or shrub that grows in chiefly tropical coastal swamps that are flooded at high tide, 

typically with numerous tangled roots above ground and forming dense thickets.

Markov Chain: A mathematical system that transitions from one state to another according to certain 

probabilistic rules. Its defining characteristic is that no matter how the process reached its present 

state, the possible future states are fixed. They are used to model randomness in biological and 

economic systems. 
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Marine Hydrokinetic Technologies (MHK): The use of movement or temperature gradients of water to 

generate electricity in the ocean.

Marine Seismic Survey: A type of geological and geophysical survey that uses a variety of acoustic sources 

to image sediment and rock deep below the sea floor.

Maritime Heritage: The study of our past, both recent and ancient, in the context of the marine 

environment; study of the history of vessels, trade, transport, seaports, migration, navies, and sea 

battles, among other topics.

Marsh: A type of wetland which is dominated by grasses and other herbaceous plants; may be freshwater, 

brackish, or saltwater, and may be located inland or along the coast. 

Masking: The effect of an acoustic source interfering with the reception and detection of an acoustic 

signal of biological importance to a receiver.

Mechanical Wave: A wave, such as sound, that is not capable of transmitting its energy through a vacuum. 

They require a medium in order to propagate their energy from one location to another. 

Melon (as in Odontocetes): A globular fatty organ in certain whale species that gives shape to the domed 

forehead, focuses and modulates the animal’s vocalizations, and acts as a sound lens; it is a key organ 

involved in communication and echolocation. 

Merchantman: A merchant or trading ship that transports cargo or carries passengers for hire. 

Mesopelagic: Also known as the middle open ocean, this zone stretches from the bottom of the epipelagic 

down to the point where sunlight cannot reach. The deep end of this zone is approximately 1,000 m 

(3,300 feet) deep.

Metapopulation: Consists of a group of spatially separated populations of the same species which 

interact at some level. Among certain marine fish species, for example, populations may be spatially 

separated and independent, but spatial overlap occurs during breeding periods, allowing for gene 

flow between the distinct populations.

Midden: An old dump for domestic waste which may consist of animal bone, human excrement, botanical 

material, mollusk shells, sherds, lithics, and other artifacts and ecofacts associated with past human 

occupation.

Midwater: Mesopelagic and bathypelagic (see definitions above) zones of the open ocean.

Migratory Corridor: Areas and seasons within which a substantial portion of a species or population is 

known to migrate; for aquatic species the corridor is typically delimited on one or both sides by land 

or ice. 

Minimum Population Estimate: An estimate of the number of animals in a stock that: 

(A) is based on the best available scientific information on abundance, incorporating the precision and 

variability associated with such information; and

(B) provides reasonable assurance that the stock size is equal to or greater than the estimate.

Minority Population: A population in which the percentage of minorities exceeds 50 percent or is 

substantially higher than the percentage of minorities in the general population or other appropriate 

unit of geographic analysis.

Mollusk: Phylum of macroinvertebrates including gastropods (e.g., sea snails, whelks, limpets, abalone), 

bivalves (e.g., clams, mussels, oysters, scallops), cephalopods (e.g., squid, octopus), and chitins.
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Molt: The process of shedding feathers, fur, or skin that will be replaced by a new growth. 

Motile: Capable of self-powered motion.

Muktuk/maktak: Fried whale blubber. 

M-weighting Function: Sound frequency weighting function for marine mammals based on a literature 

review of their physiological and behavioral responses to anthropogenic sound. Applied in a similar 

way as A-weighting for noise level assessments for humans (see definition for A-weighting function).

Mysticete: A taxonomic suborder of cetaceans; whales that have two blowholes and baleen plates instead 

of teeth. 

Nacelle: Housing for the generator, gearbox, and other parts of a wind turbine.

National Register of Historic Places (NRHP): The official list of the nation's historic places worthy of 

preservation. Authorized by the National Historic Preservation Act of 1966, the National Park Service's 

NRHP is part of a national program to coordinate and support public and private efforts to identify, 

evaluate, and protect America's historic and archeological resources.

National Wildlife Refuge: A designation for protected areas that are managed by the U.S. Fish and Wildlife 

Service. These public lands and waters are set aside to conserve America's wild animals and plants.

Neritic: Relating to or denoting the shallow part of the sea near a coast and overlying the continental 

shelf.

Nesting: The process of building or occupying a nest (i.e., a structure built by certain animals to hold eggs, 

offspring, and, oftentimes, the animal itself). 

Noise: An undesirable sound, one that interferes with communication, is intense enough to damage 

hearing, or is otherwise intrusive or objectionable to certain living organisms, including humans.

Non-impulsive Sound: Sounds that can be broadband, narrowband or tonal, brief or prolonged, 

continuous or intermittent, and typically do not have a high peak sound pressure with rapid rise/decay 

time as impulsive sounds do.

Nursery Area: A location, usually offering plentiful food and some level of protection from predation, in 

which the juveniles of a marine species undergo growth and development.

Nutrient Cycling: Movement of organic and inorganic materials through different components of a cell, 

community, or ecosystem, which can be cycled and reutilized by some of these components. 

Ocean Acidification: The process in which the acidity, a measure of hydrogen ion concentration (pH), of 

seawater increases as a result of absorbing carbon dioxide (CO2).

Ocean Economy: Economic activity which indirectly or directly uses the ocean (or Great Lakes) as an input.

It consists of six sectors: marine construction; living resources; offshore mineral extraction; ship and 

boat building; tourism and recreation; and marine transportation.

Ocean Thermal Energy Conversion (OTEC): A process or technology to power a turbine to produce 

electricity by harnessing the temperature differences (i.e., thermal gradients) between ocean surface 

waters and deep ocean waters.

Octave: A series of eight notes occupying the interval between, and including, two notes, one having twice 

or half the frequency of vibration of the other.

Odobenid: Organisms belonging to the family Odobenidae. The only living species is the walrus.
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Odontocete: A taxonomic suborder of cetaceans; whales that have teeth (e.g., the orca) and one opening 

at their blowhole. 

Offshore Waters: Marine waters outside the territorial boundaries of a state. 

Ordnance: Military supplies including weapons, ammunition, combat vehicles, and maintenance tools and 

equipment.

Ostracod: A class of crustaceans that has several pairs of legs and a body made up of sections that are 

covered in a hard outer shell. 

Otariid: Eared seals. This family includes sea lions and fur seals. 

Otolith: Also known as “earstones”, they are hard, calcium carbonate structures located directly behind 

the brain of bony fishes; involved in sensing gravity and movement. Alternating bands develop over 

time that can be read like tree rings to determine a specimen’s age, which is important information 

in managing the sustainable harvest of fish stocks. 

Overwintering: The process of organisms adapting to and surviving winter conditions, such as freezing 

temperatures, ice, snow, and less available food. 

Pack Ice: Any area of detached sea ice (i.e., ice formed by freezing of sea water) that is not land fast; it is 

mobile by virtue of not being attached to the shoreline or something else.

Palustrine: Relating to a system of inland freshwater wetlands, such as marshes, swamps, and lake shores, 

and characterized by the presence of trees, shrubs, or emergent vegetation. 

Passband: Frequency bands obtained by splitting a spectrum into 1 Hz wide bands. 

Passive Sonar: A method for detecting acoustic signals in an underwater environment, usually the ocean. 

The difference between passive and active sonar is that a passive sonar system emits no signals; 

instead, its purpose is to detect the acoustic signals emanating from external sources.

Patch Reef: Small, isolated reefs (see definition below) that grow up from the open bottom of the island 

platform or continental shelf. They usually occur between fringing reefs and barrier reefs.

Peak Pressure: The maximum value reached by sound pressure (see definition below); referred to as the 

Lpeak or sometimes Lpk. 

Peak-to-peak Sound Pressure: The difference between the maximum and minimum instantaneous sound 

pressure (see definition below), possibly filtered in a stated frequency band, attained by an impulsive 

sound, p(t).

Pelagic: Relating to, living in, or found on the open sea, away from land, where water is deep; oceanic. 

Permanent Threshold Shift (PTS): Permanent elevation in hearing threshold with physical damage to the 

sound receptors in the ear lasting indefinitely; in some cases, there can be total or partial deafness, 

whereas in other cases the animal has an impaired ability to hear sounds in specific frequency ranges. 

Period (as related to sound): Duration of 1 cycle: TT = 1/ ff [s], where T = time period to complete one cycle 

of an oscillation, ff = frequency, and s = second. It is related to wavelength by TT=λ/v, where, λ = 

wavelength (lambda), and v = velocity.

Petroglyphs: Prehistoric rock carvings.

Phocid: Earless seals or “true seals” that can be identified by their lack of external ear flaps.
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Photic Zone: Part of a body of water where enough light penetrates for photosynthesis to occur in 

phytoplankton.

Photosynthesis: Process by which green plants, algae, diatoms, and certain forms of bacteria (e.g., 

cyanobacteria) manufacture the carbohydrate glucose (C6H12O6) from carbon dioxide and water, using 

energy captured from sunlight by chlorophyll, and releasing excess oxygen as a byproduct.

Phylum (p. phyla): Major taxonomic category that ranks just above class and just below kingdom (as in 

plant, animal, and fungus kingdoms) in the taxonomic hierarchy; it classifies organisms by their 

fundamental body plan.

Physiology: The normal functions of living organisms and their anatomical structures.

Phytoplankton: Microscopic organisms that live in both saltwater and freshwater aquatic environments; 

like all green plants, they contain the pigment chlorophyll to convert sunlight via the process of 

photosynthesis into carbohydrates (i.e., food, organic matter, and chemical energy); phytoplankton 

are critically important in aquatic ecosystems and form the base of the aquatic food web or pyramid.

Pillbox: Small concrete forts used by armies as outposts or guard posts. 

Pinger: Underwater signaling device or locator beacon; they have short-duration chirp signals in the 10 s 

of kHz range at moderate source levels (160-180 dB re: 1 micropascal [μPa] @ 1 m).

Pinniped: Marine mammals that include the true seals, eared seals, sea lions, and walruses.

Piscivorous: Referring to organisms that primarily eat fish.

Planktivorous: Referring to organisms that primarily consume small invertebrates (e.g., plankton such as 

krill, zooplankton).

Plankton: Organisms, including both plants and animals (i.e., autotrophs and heterotrophs), that drift in 

water in the oceans, seas, rivers, and lakes.

Plunge Diving: A seabird foraging technique that involves rapidly diving into deep waters while in flight in 

order to hunt for prey; practiced by gannets and boobies, among other species.

Pod: A social group of whales. 

Population: Group of individual organisms of the same plant, animal, or microorganism species capable 

of interbreeding and occupying the same geographic area or ecosystem; or, the size (i.e., number of 

individuals) in any given population; members of a given population are typically more closely related 

to one another genetically than to individuals of other populations within the same species. 

Potential Biological Removal (PBR) Level: Defined by the MMPA as the maximum number of animals, not 

including natural mortalities, that may be removed from a marine mammal stock while allowing that 

stock to reach or maintain its optimum sustainable population.

Porifera: Macroinvertebrate animal phylum composed of sponges.

Precision: The degree to which separate measurements or models of the same subject are close in value. 

Precocial: Offspring requiring lower levels of parental care.

Primary Constituent Element (PCE): The physical and biological features of a habitat that a species needs 

to survive and reproduce. Used in definitions of designated critical habitat.

Producer Surplus: The value of a good or service in excess of the costs of production.
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Programmatic: Describes any broad or high-level National Environmental Policy Act (NEPA) review; it is 

not limited to a NEPA review for a particular project. Programmatic NEPA reviews assess the general 

environmental impacts of proposed policies, plans, programs, or suites of projects for which 

subsequent actions will be implemented either based on the Programmatic Environmental 

Assessment or Programmatic Environmental Impact Statement, or based on subsequent NEPA

reviews tiered from the programmatic review (e.g., a site- or project- specific document).

Project Cargo: Large, heavy, high value or critical pieces of equipment for a project.

Propagation Loss: Reduction in sound pressure level (SPL) between two designated locations in a sound 

transmission system, one location often being at a reference location from the source. Also known as 

propagation transmission loss.

Propagules: Any material that functions in growing an organism to the next stage in its life cycle, such as 

by dispersal. The propagule is usually distinct in form from the parent organism.

Propeller Singing: The resonance between the local natural frequency of the propeller blade tip and the 

vortex shedding frequency at trailing edge of the blade. Propeller singing creates very intensive levels 

of radiated noise.

Protected Species: An animal or plant which it is forbidden by federal law to harm or destroy, e.g., 

endangered species. 

Pseudofeces: Mucous-coated grit expelled by filter-feeding gastropod mollusks, distinct from actual feces.

Pulse (as related to sound): A single segment of a periodic signal that consists of (potentially) repeating 

segments with defined beginning and end points and is, typically, short in duration. Pulses are not 

necessarily impulsive. 

Pulse Length: For impulsive (pulsed) sound (e.g., airguns, pile driving), the pulse length is often taken as 

the 90 percent pulse energy duration T90%, which is the time between the 5 percent and 95 percent 

points on the cumulative energy curve. 

P-wave: Also called primary waves, these are mechanical waves that are longitudinal in nature. 

Received Level: Amount of sound energy actually reaching a receiver such as a modeled animal; the 

greater the transmission loss, the lower the received sound level at any given location.

Red Tide: A common term used for harmful algal blooms, which can be dangerous to people and deadly 

for fish due to potent neurotoxins released by the dinoflagellate Karenia brevis.

Reef: A ridge of jagged rock, coral, or sand just above or below the surface of the sea.

Reef Crest: The highest (i.e., most shallow) part of the reef which lies between the shoreward, protected 

back reef zone and the outer fore reef zone (see definitions above).

Reef Flat: Occupies the inshore side of the bank reef (see definition above). This consists of broken coral 

skeletons and coralline algae and excludes most other organisms due to the inhospitable, heavy surf 

that often characterizes this area.

Reef Slope: Area of high coral cover and moderate to low wave energy on the fringing reef.

Reproductive Area: Locations and seasons within which a particular species or population selectively 

mates, gives birth, or is found with neonates or other sensitive age classes.

Reserved Right: The doctrine that holds that Native Americans retain all rights not explicitly revoked in 

treaties or other legislation.
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Rise Time: The amount of time it takes for a signal to change from static pressure to high pressure.

Rookery: Large, clustered nesting colony, generally of gregarious seabirds, wading birds, and pinnipeds. 

Salp: Semi-transparent barrel-shaped marine animals that move through the water by contracting bands 

of muscles which ring the body. They belong to the subphylum Tunicata, a group of marine 

macroinvertebrates also known as sea squirts. 

Salt Marsh: Coastal wetlands that are flooded and drained by salt water moved by the tides; the soil may 

be composed of deep mud and peat.

Sandbar: Along the seashore, a ridge of sand or coarse sediment connected to the shoreline or resting 

offshore that is submerged or partially exposed; generally narrow and straight and formed by the 

breaking of waves moving material from the shoreline.

Sandflat: A flat, marshy, or barren tract of land that is alternately covered and uncovered by the tide and 

consisting of unconsolidated sediment mostly of mud and sand. 

Sea floor: The solid surface underlying a sea or ocean.

Seabirds: Birds which spend much of their lives at sea foraging over pelagic habitat (i.e., open sea), often 

thousands of kilometers from their nesting grounds.

Seamount: Undersea mountains formed by volcanic activity.

Sediment: A naturally occurring material that is broken down by processes of weathering and erosion and 

subsequently transported by the action of wind, water, or ice or by the force of gravity.

Seine Net: A large mesh with sinkers on one edge and floats on the other that hangs vertically in the water 

and is used to enclose and catch fish when its ends are pulled together or are drawn ashore.

Semelparous: Organisms that die after spawning only once, such as Pacific salmonids.

Sessile: Non-mobile, or attached, organisms such as adult coral polyps.

Shelf Break: The point of the first major change in gradient at the outermost edge of the continental shelf 

(see definition above); its depth, distance from shore, and configuration are highly variable.

Shoal: A shallow place in a river, sea, or other body of water caused by a submerged bank or bar of sand 

or other unconsolidated material deposited on the substrate

Shorebirds: A distinct taxonomic subset of coastal birds, such as sandpipers, plovers, sanderlings, and 

godwits which forage on sandy shores at the water’s edge.

Sirenian: An order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine 

wetlands, and coastal marine waters. Sirenians currently comprise the families Dugongidae (e.g., the 

dugong) and Trichechidae (e.g., manatees) with a total of four species.

Social Surplus: The value of a good or service in excess of the costs of acquisition or production.

Sonar: A technique that uses sound propagation to navigate (e.g., submarines), communicate with, or 

detect objects on or under the surface of the water, such as other vessels.

Sound: Vibrations that travel through the air or water and can be heard when they reach a person's or 

animal's ear.

Sound Exposure Level (SEL): The time-integral of the squared acoustic pressure over a duration (T).
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Sound Pressure Level (SPL): The root-mean-square (rms) pressure level in a stated frequency band over 

a specified time window (T; s).

Source Level: Amount of sound radiated by a sound source, 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 stated as a relative intensity in decibels 

(dB). In underwater sound, decibels are referenced to a pressure of 1 μPa; thus, sound level is 

reported in units of dB re 1 μPa @ 1 m.

South Pacific Gyre: A distinct area of the Earth’s system of rotating ocean currents bounded by the 

equator to the north, Australia to the west, the Antarctic Circumpolar Current to the south, and South 

America to the east.

Spawn: The mass of eggs deposited by fishes, amphibians, mollusks, crustaceans, etc.; the release or 

deposit of eggs.

Species: The most basic unit in the hierarchical system of taxonomy, a group of organisms that can and 

do reproduce with one another in nature and produce offspring that are fertile.

Spectral Density: The distribution of a sound’s power with frequency is described by the sound’s 

spectrum. The sound spectrum can be split into a series of adjacent frequency bands with a width of 

1 Hz (called passbands), which yields the power spectral density of the sound.

Speed: The distance travelled per unit time cc = λλ/TT = λλ × ff where c = the speed of sound [m/s], ff = 

frequency (Hz), λ = wavelength (m), and TT = time (s).

Spermaceti: The solid wax found in the head cavity of the sperm whale.

Spherical Spreading Loss: With regard to spherical sound waves emitted by a point source, refers to that 

portion of the transmission loss due to the divergence, that is, spreading, of sound waves in 

accordance with a system’s configuration. Also known as divergence loss.

Spur and Groove: Geomorphic feature of many coral reefs, consisting of ridges or “spurs” of coral 

separated by channels or “grooves”; grooves are often characterized by sediments such as sand or 

rubble. 

State Historic Preservation Office/Officer (SHPO): Entities within each state and U.S. territory that 

administer the state historic preservation program, a state and National Register of Historic Places 

Program, a Historic Preservation Fund grant program, a data management program, review and 

compliance, and other programs. The latter term refers to the individual who directs that office and 

oversees management of each of its programs.

Statocysts: Sac-like organs with sensory cilia. 

Stock: In fisheries, it refers to a particular fish population of a given species that is more or less genetically 

isolated from other stocks of the same species, such as those associated with a particular river or 

tributary. For marine mammals, it is a group of individuals of the same species or smaller taxa in a 

common spatial arrangement that interbreed when mature.

Stranding: The term may refer to any of the following:

• A marine mammal that is on the shore and unable to return to the water under its own power;

• A marine mammal that is on the shore and, although able to return to the water, is in need of 

apparent medical attention;
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• A marine mammal in the water that cannot return to its natural habitat without assistance; or

• A dead marine mammal on the beach or in the water.

Strategic Stock (under the MMPA): Defined by the MMPA as a marine mammal stock: 

• For which the level of direct human-caused mortality exceeds the potential biological removal 

level (see definition above);

• Which, based on the best available scientific information, is declining and is likely to be listed as a 

threatened species under the ESA within the foreseeable future; or

• Which is listed as a threatened or endangered species under the ESA, or is designated as depleted 

under the MMPA.

Strike Quota: Under international agreement, refers to the limitation on the number of bowhead whales 

that may be struck by subsistence hunters, and is the sum total of the whales that are successfully 

and unsuccessfully landed.

Submarine Canyon: Narrow, steep-sided valleys that cut into continental slopes and continental rises of 

the oceans. They originate either within continental slopes or on a continental shelf.

Submerged Cultural and Historic resources: Objects found on the sea floor, lake, or river beds with 

historic, pre-historic, or culturally significant values.

Subsistence: Subsistence uses of wild resources are defined as “noncommercial, customary and 

traditional uses” for a variety of purposes. These include: Direct personal or family consumption as 

food, shelter, fuel, clothing, tools, or transportation; for the making and selling of handicraft articles 

out of nonedible by-products of fish and wildlife resources taken for personal family consumption; 

and for the customary trade, barter, or sharing for personal or family consumption. 

Substrate: Surface or material on or from which an organism lives, grows, or obtains its nourishment; also, 

the material or sediments that rest at the bottom of a stream, lake, or ocean. 

Subtidal Zone: On a coastline, the area that lies below the intertidal zone (see definition above) and is 

almost continuously submerged. 

Suspension Feeder: Animals that eat particles of organic matter that are suspended in water.

S-wave: Also called secondary waves, these are mechanical waves that are transverse in nature.

Swim Bladder: In fish, gas-filled internal cavity near the ears that deforms with the pressure wave and 

allows fish to sense the pressure impact of sound.

Taxon (pl. taxa): Units used in the science of biological classification, or taxonomy. A taxonomic group of 

any rank, such as a species, family, or class.

Taxonomy: Science of naming, describing, and classifying organisms, including all plants, animals, and 

microorganisms in the biosphere.

Temporary Threshold Shift (TTS): The mildest form of hearing impairment; exposure to loud sound 

resulting in a non-permanent (i.e., reversible) elevation in hearing threshold, making it more difficult 

to hear sounds; TTS can last from minutes or hours to days; the magnitude of the TTS depends on the 

level and duration of the sound exposure, among other considerations.

Territorial Sea: Defined as a belt of coastal waters extending 12-nautical miles from the baseline, usually 

the low-water line, along the coast. 
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Tidal Flat: Intertidal, non-vegetated, soft sediment habitats, found between mean high-water and mean 

low-water spring tide datums and generally located in estuaries and other low energy marine 

environments.

Thermal Refugium (pl. refugia): A place that serves as a shelter for organisms from adverse temperatures 

(e.g., in a stream).

Thermocline: Transition layer between warmer mixed water at the ocean’s surface and cooler deep water 

below. 

Thicket: Dense groups of corals. 

Threatened: A species is considered threatened if it is likely to become an endangered species under the 

ESA within the foreseeable future.

Tonal Sound: Sounds with discrete frequencies, such as music notes.

Traditional Cultural Places: Also referred to as “Traditional Cultural Properties”, TCPs are historic 

properties that derive their cultural significance from the role the property plays or played in a 

community’s historically rooted beliefs, customs, and practices. 

Transducer: Any device that converts one form of energy into a readable signal.

Transmission Loss: A measure, in decibels, of the decrease in sound level between a source and a receiver 

some distance away. Geometric spreading of acoustic waves is the predominant way by which 

transmission loss occurs. Transmission loss also happens when the sound is absorbed and scattered 

by the seawater, and reflected at the water surface and within the seabed. Transmission loss depends 

on the acoustic properties of the ocean and seabed; its value changes with frequency.

Treaty Tribe: Federally recognized tribe that has retained its right to hunt, fish, and gather under a treaty 

signed with the federal government.

Tribal Sovereignty: The right of American Indians and Alaska Natives to govern themselves. The U.S. 

Constitution recognizes Indian tribes as distinct governments and they have, with a few exceptions, 

the same powers as federal and state governments to regulate their internal affairs. 

Trophic Level: The position an organism occupies in a food chain. A food chain is a succession of organisms 

that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is 

the number of steps it is from the start of the chain.

Tunicate: Macroinvertebrate animal phylum including sea squirts or sea pork.

Tympanum: Membrane, or eardrum, in certain animals. 

Umiak: Seal skin boat. 

Unavoidable Adverse Impact: Effects on the human environment that would remain even after mitigation

measures and BMPs have been applied.

Undertaking: A project, activity, or program funded in whole or in part by a federal agency, including 

those carried out by or on behalf of a federal agency; those carried out with federal assistance; those 

requiring a federal permit, license, or approval; and those subject to state or local regulation 

administered pursuant to a delegation or approval by a federal agency. 

Unregulated Fishing: Occurs in areas or for fish stocks for which there are no applicable conservation or 

management measures and where such fishing activities are conducted in a manner inconsistent with 
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the responsibilities of nation-states for the conservation of living marine resources under 

international law. Unregulated fishing occurs in marine regions outside the EEZs of nation-states.

Unreported Fishing: Fishing activities that are not reported or are misreported to relevant authorities in 

contravention of national laws and regulations or reporting procedures of a relevant regional fisheries 

management organization. 

Upwelling: A process in which deep, cold water rises toward the surface. It occurs in the open ocean and 

along coastlines. 

Usual and Accustomed (U&A) Places: Lands adjacent to streams, rivers, or shorelines to which a tribe

usually travels or is accustomed to travel for the purpose of taking fish.

Vessel Wake: Waves created by the hull of a ship as it moves through the water. Depending on hull design, 

speed, vessel weight, and power supply, the wake of a vessel can produce anywhere from a minimal 

flow of water and rippling chop to swelling waves of significant size.

Vestibular Apparatus: In vertebrates, the structure of the inner ear involved in balance. 

Viewshed: A subset of a landscape unit that consists of all the surface areas visible from an observer’s 

viewpoint.

Viscosity: Quantity that describes a fluid’s resistance to flow. 

Viviparous: Animals that give birth to developed, live young, instead of producing eggs. 

Water Column: Conceptual vertical area of water extending from the surface of the ocean, river, or lake 

to the bottom substrate or sediment. Many physical, chemical, and biological aquatic phenomena are 

characterized by their relative and/or absolute positions in the water column.

Waterfowl: Birds which spend much of their lives on the water’s surface in both freshwater and saltwater 

environments. Specifically refers to ducks, geese, and swans. 

Watershed: An area of land that drains or “sheds” water into a specific watercourse (i.e., a river or 

stream), such as the Missouri River watershed or the Ohio River watershed.

Wavelength: Spatial distance between two successive ‘peaks’ in a propagating wave: λλ [m]. It is related 

to sound speed c and frequency ff by λ= cc/ff.

Weighting Function: In acoustical analysis, a weighting function is used to correlate objective sound level 

meter measurements with subjective responses to sound in the subject organisms (such as marine 

mammals) under study.

Whelping: The process of a mammal giving birth, such as female polar bears birthing their cubs.

Willingness to Pay: The amount users are hypothetically willing to pay for goods, services, or information. 

Commonly used to monetize goods, services, or information without clear market values. 

Zero-to-peak Sound Pressure/Peak Sound Pressure: Decibel level of the maximum instantaneous 

acoustic pressure in a stated frequency band attained by an acoustic pressure signal, p(t).

Zooplankton: A type of heterotrophic (i.e., non-photosynthesizing) plankton that ranges from microscopic 

organisms to macroinvertebrates such as jellyfish; zooplankton drift or float with marine currents. 

Zooplankton are heterotrophs (i.e., they cannot produce their own food via photosynthesis) and must 

obtain their energy by consuming other organisms. 

Zooxanthellae: Unicellular, golden-brown algae (e.g., dinoflagellates) that live either in the water column 

as plankton or symbiotically inside the tissue of other organisms, such as coral polyps.