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Glossary of Terms


How many individuals (of a particular species) live in a particular area, typically expressed as an 'abundance estimate' since it is rare that we know exactly how many are there. This is different from the common use of the word to indicate ‘a large number’.

Carrying capacity 

The maximum number of individuals of a species that can be supported by available resources for a specific population and range. 

Depletion level 

This term indicates a population’s current size relative to its original, undisturbed level, usually assumed to be at carrying capacity.
Note: the term relative abundance is used in some IWC graphs and tables instead of ‘depletion level’.

Extinction (biological)

The loss of all members of a species.

Feeding group 

Individuals distinguished by feeding regularly or primarily in a particular geographic area or region. In certain cases, such groups may be treated as a management unit.


A group of individuals of the same species that typically live and interbreed in a particular habitat or region and are isolated to some extent from other groups within the species.
Note: The IUCN uses a different definition for the term 'population' in its Red List assessments, where 'population' is generally equivalent to 'species', although their usage of 'subpopulation' is generally equivalent to that below, i.e. geographically or otherwise distinct groups in the overall species population between which there is little demographic or genetic exchange (mixing).

Population estimate(s) or population size estimate(s) 

An alternative and generally equivalent term to abundance or abundance estimate used to indicate the number of individuals (of a particular population or subgroup of a species) estimated to live in a particular area.

Population status 

An overall assessment/evaluation of a population’s [or sub-group’s] abundance and state of recovery or decline. 

Population structure/stock structure 

The presence of consistent differences between subpopulations – such as geographic, genetic, or acoustic characteristics that can be used to infer the level of interbreeding or interactions among the subpopulations.

Range (geographical)

The geographical region in which a species or species subdivision (population or subpopulation) is naturally found.


A sustained increase in abundance, typically after numbers were reduced due to natural causes or human causes. Sometimes recovery is evaluated relative to particular conservation or management goals, such as an increase to pre-depletion abundance. 


A term used in the IWC’s founding document, the International Convention on the Regulation of Whaling. In current usage by the IWC Scientific Committee, a stock is generally equivalent to a 'subpopulation'. This usage derives from the scientists, many of whom were originally fisheries biologists, involved in the early efforts of the IWC to manage sustainable hunting of whale populations.


A distinct component of a population, which can be based on geographic,  genetic, morphological, and/or behavioural differences.