Categories and Criteria of the Red List of the IUCN
The Red List of the IUCN contains endangered animal and plant species. Unfortunately, it also includes many shark species. The degree of endangerment to the various shark species is determined on the basis of the well documented criteria listed below. The present criteria are Version 3.1 (2001).
EX
Extinct
A taxon is Extinct when there is no reasonable doubt that the last individual has died. A taxon is presumed Extinct when exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual. Surveys should be over a time frame appropriate to the taxon's life cycle and life form.
EW
Extinct in the Wild
A taxon is Extinct in the Wild when it is known only to survive in cultivation, in captivity or as a naturalized population (or populations) well outside the past range. A taxon is presumed Extinct in the Wild when exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual. Surveys should be over a time frame appropriate to the taxon's life cycle and life form.
CR
Critically Endangered
A taxon is Critically Endangered when the best available evidence indicates that it meets any of the criteria A to E for Critically Endangered (see below), and it is therefore considered to be facing an extremely high risk of extinction in the wild.
A
Reduction in population size based on any of the following:
A1
An observed, estimated, inferred or suspected population size reduction of 90 % over the last 10 years or three generations, whichever is the longer, where the causes of the reduction are clearly reversible AND understood AND ceased, based on (and specifying) any of the following:
A1a
direct observation
A1b
an index of abundance appropriate to the taxon
A1c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A1d
actual or potential levels of exploitation
A1e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
A2
An observed, estimated, inferred or suspected population size reduction of 80 % over the last 10 years or three generations, whichever is the longer, where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of (a) to (e)
A2a
direct observation
A2b
an index of abundance appropriate to the taxon
A2c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A2d
actual or potential levels of exploitation
A2e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
A3
A population size reduction of 80 %, projected or suspected to be met within the next 10 years or three generations, whichever is the longer (up to a maximum of 100 years), based on (and specifying) any of (b) to (e)
A3b
an index of abundance appropriate to the taxon
A3c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A3d
actual or potential levels of exploitation
A3e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
A4
An observed, estimated, inferred, projected or suspected population size reduction of 80 % over any 10 year or three generation period, whichever is longer (up to a maximum of 100 years in the future), where the time period must include both the past and the future, and where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of (a) to (e):
A4a
direct observation
A4b
an index of abundance appropriate to the taxon
A4c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A4d
actual or potential levels of exploitation
A4e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
B
Geographic range in the form of either B1 (extent of occurrence) OR B2 (area of occupancy) OR both:
B1
Extent of occurrence estimated to be less than 100 km², and estimates indicating at least two of a-c:
B1a
Severely fragmented or known to exist at only a single location.
B1b
Continuing decline, observed, inferred or projected, in any of the following:
B1b(i)
extent of occurrence
B1b(ii)
area of occupancy
B1b(iii)
area, extent and/or quality of habitat
B1b(iv)
number of locations or subpopulations
B1b(v)
number of mature individuals.
B1c
Extreme fluctuations in any of the following:
B1c(i)
extent of occurrence
B1c(ii)
area of occupancy
B1c(iii)
number of locations or subpopulations
B1c(iv)
number of mature individuals
B2
Area of occupancy estimated to be less than 10 km², and estimates indicating at least two of a-c:
B2a
Severely fragmented or known to exist at only a single location.
B2b
Continuing decline, observed, inferred or projected, in any of the following:
B2b(i)
extent of occurrence
B2b(ii)
area of occupancy
B2b(iii)
area, extent and/or quality of habitat
B2b(iv)
number of locations or subpopulations
B2b(v)
number of mature individuals.
B2c
Extreme fluctuations in any of the following:
B2c(i)
extent of occurrence
B2c(ii)
area of occupancy
B2c(iii)
number of locations or subpopulations
B2c(iv)
number of mature individuals
C
Population size estimated to number fewer than 250 mature individuals and either:
C1
An estimated continuing decline of at least 25 % within three years or one generation, whichever is longer, (up to a maximum of 100 years in the future) OR
C2
A continuing decline, observed, projected, or inferred, in numbers of mature individuals AND at least one of the following (a-b):
C2a
Population structure in the form of one of the following:
C2a(i)
no subpopulation estimated to contain more than 50 mature individuals, OR
C2a(ii)
at least 90 % of mature individuals in one subpopulation.
C2b
Extreme fluctuations in number of mature individuals.
D
Population size estimated to number fewer than 50 mature individuals.
E
Quantitative analysis showing the probability of extinction in the wild is at least 50 % within 10 years or three generations, whichever is the longer (up to a maximum of 100 years).
EN
Endangered
A taxon is Endangered when the best available evidence indicates that it meets any of the criteria A to E for Endangered (see below), and it is therefore considered to be facing a very high risk of extinction in the wild:
A
Reduction in population size based on any of the following:
A1
An observed, estimated, inferred or suspected population size reduction of 70 % over the last 10 years or three generations, whichever is the longer, where the causes of the reduction are clearly reversible AND understood AND ceased, based on (and specifying) any of the following:
A1a
direct observation
A1b
an index of abundance appropriate to the taxon
A1c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A1d
actual or potential levels of exploitation
A1e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
A2
An observed, estimated, inferred or suspected population size reduction of 50 % over the last 10 years or three generations, whichever is the longer, where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of (a) to (e):
A2a
direct observation
A2b
an index of abundance appropriate to the taxon
A2c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A2d
actual or potential levels of exploitation
A2e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
A3
A population size reduction of 50 %, projected or suspected to be met within the next 10 years or three generations, whichever is the longer (up to a maximum of 100 years), based on (and specifying) any of (b) to (e):
A3b
an index of abundance appropriate to the taxon
A3c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A3d
actual or potential levels of exploitation
A3e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
A4
An observed, estimated, inferred, projected or suspected population size reduction of 50 % over any 10 year or three generation period, whichever is longer (up to a maximum of 100 years in the future), where the time period must include both the past and the future, and where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of (a) to (e):
A4a
direct observation
A4b
an index of abundance appropriate to the taxon
A4c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A4d
actual or potential levels of exploitation
A4e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
B
Geographic range in the form of either B1 (extent of occurrence) OR B2 (area of occupancy) OR both:
B1
Extent of occurrence estimated to be less than 5000 km², and estimates indicating at least two of a-c:
B1a
Severely fragmented or known to exist at no more than five locations.
B1b
Continuing decline, observed, inferred or projected, in any of the following:
B1b(i)
extent of occurrence
B1b(ii)
area of occupancy
B1b(iii)
area, extent and/or quality of habitat
B1b(iv)
number of locations or subpopulations
B1b(v)
number of mature individuals.
B1c
Extreme fluctuations in any of the following:
B1c(i)
extent of occurrence
B1c(ii)
area of occupancy
B1c(iii)
number of locations or subpopulations
B1c(iv)
number of mature individuals
B2
Area of occupancy estimated to be less than 500 km², and estimates indicating at least two of a-c:
B2a
Severely fragmented or known to exist at no more than five locations.
B2b
Continuing decline, observed, inferred or projected, in any of the following:
B2b(i)
extent of occurrence
B2b(ii)
area of occupancy
B2b(iii)
area, extent and/or quality of habitat
B2b(iv)
number of locations or subpopulations
B2b(v)
number of mature individuals.
B2c
Extreme fluctuations in any of the following:
B2c(i)
extent of occurrence
B2c(ii)
area of occupancy
B2c(iii)
number of locations or subpopulations
B2c(iv)
number of mature individuals
C
Population size estimated to number fewer than 2500 mature individuals and either:
C1
An estimated continuing decline of at least 20 % within five years or two generations, whichever is longer, (up to a maximum of 100 years in the future) OR
C2
A continuing decline, observed, projected, or inferred, in numbers of mature individuals AND at least one of the following (a-b):
C2a
Population structure in the form of one of the following:
C2a(i)
no subpopulation estimated to contain more than 50 mature individuals, OR
C2a(ii)
at least 90 % of mature individuals in one subpopulation.
C2b
Extreme fluctuations in number of mature individuals.
D
Population size estimated to number fewer than 250 mature individuals.
E
Quantitative analysis showing the probability of extinction in the wild is at least 20 % within 20 years or five generations, whichever is the longer (up to a maximum of 100 years).
VU
Vulnerable
A taxon is Vulnerable when the best available evidence indicates that it meets any of the criteria A to E for Vulnerable (see Section V), and it is therefore considered to be facing a high risk of extinction in the wild.
A
Reduction in population size based on any of the following:
A1
An observed, estimated, inferred or suspected population size reduction of 50 % over the last 10 years or three generations, whichever is the longer, where the causes of the reduction are clearly reversible AND understood AND ceased, based on (and specifying) any of the following:
A1a
direct observation
A1b
an index of abundance appropriate to the taxon
A1c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A1d
actual or potential levels of exploitation
A1e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
A2
An observed, estimated, inferred or suspected population size reduction of 30 % over the last 10 years or three generations, whichever is the longer, where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of (a) to (e):
A2a
direct observation
A2b
an index of abundance appropriate to the taxon
A2c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A2d
actual or potential levels of exploitation
A2e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
A3
A population size reduction of 30 %, projected or suspected to be met within the next 10 years or three generations, whichever is the longer (up to a maximum of 100 years), based on (and specifying) any of (b) to (e):
A3b
an index of abundance appropriate to the taxon
A3c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A3d
actual or potential levels of exploitation
A3e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
A4
An observed, estimated, inferred, projected or suspected population size reduction of 50 % over any 10 year or three generation period, whichever is longer (up to a maximum of 100 years in the future), where the time period must include both the past and the future, and where the reduction or its causes may not have ceased OR may not be understood OR may not be reversible, based on (and specifying) any of (a) to (e):
A4a
direct observation
A4b
an index of abundance appropriate to the taxon
A4c
a decline in area of occupancy, extent of occurrence and/or quality of habitat
A4d
actual or potential levels of exploitation
A4e
the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
B
Geographic range in the form of either B1 (extent of occurrence) OR B2 (area of occupancy) OR both:
B1
Extent of occurrence estimated to be less than 20,000 km², and estimates indicating at least two of a-c:
B1a
Severely fragmented or known to exist at no more than ten locations.
B1b
Continuing decline, observed, inferred or projected, in any of the following:
B1b(i)
extent of occurrence
B1b(ii)
area of occupancy
B1b(iii)
area, extent and/or quality of habitat
B1b(iv)
number of locations or subpopulations
B1b(v)
number of mature individuals.
B1c
Extreme fluctuations in any of the following:
B1c(i)
extent of occurrence
B1c(ii)
area of occupancy
B1c(iii)
number of locations or subpopulations.
B1c(iv)
number of mature individuals
B2
Area of occupancy estimated to be less than 2000 km², and estimates indicating at least two of a-c:
B2a
Severely fragmented or known to exist at no more than ten locations.
B2b
Continuing decline, observed, inferred or projected, in any of the following:
B2b(i)
extent of occurrence
B2b(ii)
area of occupancy
B2b(iii)
area, extent and/or quality of habitat
B2b(iv)
number of locations or subpopulations
B2b(v)
number of mature individuals.
B2c
Extreme fluctuations in any of the following:
B2c(i)
extent of occurrence
B2c(ii)
area of occupancy
B2c(iii)
number of locations or subpopulations
B2c(iv)
number of mature individuals
C
Population size estimated to number fewer than 10,000 mature individuals and either:
C1
An estimated continuing decline of at least 10 % within ten years or three generations, whichever is longer, (up to a maximum of 100 years in the future) OR
C2
A continuing decline, observed, projected, or inferred, in numbers of mature individuals AND at least one of the following (a-b):
C2a
Population structure in the form of one of the following:
C2a(i)
no subpopulation estimated to contain more than 1000 mature individuals, OR
C2a(ii)
all mature individuals in one subpopulation.
C2b
Extreme fluctuations in number of mature individuals.
D
Population very small or restricted in the form of either of the following:
D1
Population size estimated to number fewer than 1000 mature individuals.
D2
Population with a very restricted area of occupancy (typically less than 20 km²) or number of locations (typically five or fewer) such that it is prone to the effects of human activities or stochastic events within a very short time period in an uncertain future, and is thus capable of becoming Critically Endangered or even Extinct in a very short time period.
E
Quantitative analysis showing the probability of extinction in the wild s at least 10 % within 100 years.
NT
Near Threatened
A taxon is Near Threatened when it has been evaluated against the criteria but does not qualify for Critically Endangered, Endangered or Vulnerable now, but is close to qualifying for or is likely to qualify for a threatened category in the near future.
LC
Least Concern
A taxon is Least Concern when it has been evaluated against the criteria and does not qualify for Critically Endangered, Endangered, Vulnerable or Near Threatened. Widespread and abundant taxa are included in this category.
DD
Data Deficient
A taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of extinction based on its distribution and/or population status. A taxon in this category may be well studied, and its biology well known, but appropriate data on abundance and/or distribution are lacking. Data Deficient is therefore not a category of threat. Listing of taxa in this category indicates that more information is required and acknowledges the possibility that future research will show that threatened classification is appropriate. It is important to make positive use of whatever data are available. In many cases great care should be exercised in choosing between DD and a threatened status. If the range of a taxon is suspected to be relatively circumscribed, and a considerable period of time has elapsed since the last record of the taxon, threatened status may well be justified.
NE
Not Evaluated
A taxon is Not Evaluated when it is has not yet been evaluated against the criteria.
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