The Action Plan for Australian freshwater fishes
R. Wager and P. Jackson
Environment Australia, June 1993
ISBN 0 6421 6818 0
Appendix 5 – Revised IUCN threatened species categories
Introduction
This scheme has been proposed to replace the largely subjective conservation categories currently used by the IUCN. Conservation categories are redefined in terms of the probability of extinction within a specific time period, based on the theory of extinction times for single populations and on meaningful time scales for conservation action. Some quantitative criteria based on population biology theory are presented for each category. The authors suggest that these are appropriate for at least most larger vertebrates, and may need to be varied to suit other taxonomic groups.
Categories
In the following categories Ne = effective population and N = actual population. It is assumed that the ratio of Ne to N is 0.2.
Critical
50% probability of extinction within 5 years or 2 generations, whichever is the longer.
(1) Any two of the following criteria:
- Total population Ne< 50 (corresponding to actual N< 250);
- Population fragmented: < 2 subpopulations with Ne> 25 (N> 125) with immigration rates < 1 per generation;
- Census data of > 20% annual decline in numbers over past two years, or > 50% decline in the last generation, or equivalent projected declines based on demographic projections after allowing for known cycles.;
- Population subject to catastrophic crashes (> 50% reduction) per 5 to 10 years, or 2 to 4 generations, with subpopulations highly correlated in their fluctuations.
OR
(2) Observed, inferred or projected habitat alteration (ie degradation, loss or fragmentation) resulting in characteristics of (1).
OR
(3) Observed, inferred or projected commercial exploitation or ecological interactions with introduced species (predators, competitors, pathogens or parasites) resulting in characteristics of (1).
Endangered
20% probability of extinction within 20 years or 10 generations, whichever is the longer.
(1) Any two of the following criteria or any one criterion under Critical:
- Total population Ne< 500 (corresponding to actual N< 2500).
- Population fragmented:
- < 5 subpopulations with Ne> 100 (N> 500) with immigration rates < 1 per generation, or
- < 2 subpopulations with Ne> 250 (N> 1250) with immigration rates < 1 per generation.
- Census data of > 5% annual decline in numbers over past 5 years, or > 10% decline per generation over past 2 generations, or equivalent projected declines based on demographic data after allowing for known cycles.
- Population subject to catastrophic crashes: an average of 20% reduction per 5 to 10 years, or 2 to 4 generations, or 50% reduction per 10 to 20 years or 5 to 10 generations, with subpopulations strongly correlated in their fluctuations.
OR
(2) Observed, inferred or projected habitat alteration (ie degradation, loss or fragmentation) resulting in characteristics of (1).
OR
(3). Observed, inferred or projected commercial exploitation or ecological interactions with introduced species (predators, competitors, pathogens or parasites) resulting in characteristics of (1).
Vulnerable
10% probability of extinction within 100 years,
(1) Any two of the following criteria or any one criterion under Endangered:
- Total population Ne< 2000 (corresponding to actual N< 10000)
- Population fragmented:
- < 5 subpopulations with Ne> 500 (N> 2500) with immigration rates < 1 per generation, or
- < 2 subpopulations with Ne> 1000 (N> 5000) with immigration rates < 1 per generation.
- Census data of > 1% annual decline in numbers over past 10 years, or equivalent projected declines based on demographic data after allowing for known cycles.
- Population subject to catastrophic crashes: an average of 10% reduction per 5 to 10 years, 20% reduction per 10 to 20 years, or 50% reduction per 50 years, with subpopulations strongly correlated in their fluctuations.
OR
(2) Observed, inferred or projected habitat alteration (ie degradation, loss or fragmentation) resulting in characteristics of (1).
OR
(3) Observed, inferred or projected commercial exploitation or ecological interactions with introduced species (predators, competitors, pathogens or parasites) resulting in characteristics of (1).
Examples
Red-finned Blue-eye (Scaturiginichthys vermeilipinnis)
Suspect a 50% probability of extinction within five years.
- Four of five known populations possibly threatened by gambusia (Gambusia holbrooki). The habitat is also extremely vulnerable to modification.
Therefore list as Critical.
1. Total population roughly estimated at between 2 000 and 4 000 individuals.
- Five known geographic subpopulations of variable size. Immigration rates unknown.
- No census data available to indicate annual declines or catastrophic crashes.
List as Endangered.
2. Possible habitat modification/destruction.
Therefore list as Critical.
3. Inferred interaction with Gambusia. Possible exploitation through the aquarium trade.
Therefore list as Critical.
Overall Status: Critical
(Current Status: Endangered).
Australian Grayling (Prototroctes maraena)
Suspect a 10% probability of extinction within 100 years. Historical data indicates the species no longer occurs in a number of rivers within its former range. Barriers to migration are suspected to reduce recruitment. Spawning areas still not identified and may be limited to few rivers.
Therefore list as: Vulnerable.
1. Total population unknown. Populations vary greatly between rivers.
- No conclusive evidence for subpopulations.
- Has disappeared from some rivers. No quantitative information.
- Some evidence for genetic bottlenecks but no numerical data. Spawning success (ie recruitment) is believed to be dependent on flood events in autumn.
Not categorised due to insufficient data.
2. Habitat modification suspected as main cause of decline. May result in annual decline of 1% over last 10 years, or catastrophic population crashes. Insufficient quantitative data to confidently state any category.
Could be categorised as Vulnerable or Endangered.
3. No commercial or recreational fishing, possible interactions with introduced Salmo trutta. Anecdotal information only. Factors responsible for a decline of Victorian populations not well known.
Could be categorised as Vulnerable or Endangered.
Overall Status: Vulnerable.
(Current status: Vulnerable)
Non-parasitic Lamprey (Mordacia praecox)
Insufficient information to enable categorisation with this scheme.
General comments
Probability of extinction
The new classification is, in principle, an improvement over the current IUCN classification. It implies availability of quantitative information in terms of probability and timing of extinction. For fishes, information of this type is generally not available (yet), and categorisation relies on qualitative data and intuitive decisions. Although this scheme has the potential to become more rigorous, at present it relies on decision processes similar to systems currently in use.
Quantitative criteria (part 1)
The data required to utilise the criteria in this section are seldom available for Australian freshwater fishes. Information on population sizes are rarely available. The nature of aquatic environments makes sampling difficult and costly. Direct counts of fish are usually impossible and complicated sampling regimes must be implemented. There is little information on the numbers of geographic subpopulations and even less information on genetic subpopulations. Due to the lack of information on populations and population sizes it is very difficult to document annual declines or long term population cycles. Most information is usually qualitative.
Australian freshwater fishes usually have high fecundities, at least compared to higher vertebrates, although variation is considerable and may range from 150 to several million for similar sized fish of different species. Fishes may also exhibit: high population growth in favourable conditions; short generation times; irregular population fluctuations; and specific habitat requirements. The applicability of the criteria in this section (particularly the cut off numbers for effective population size) to fishes is unknown and should be investigated so that the full benefit of this scheme can be achieved.
Habitat Alteration, commercial exploitation or ecological interactions (parts 2 and 3)
These sections allow intuitive decisions to be made in the absence of quantitative data required above. At present most species categorisations of freshwater fishes would be based on these criteria.
Other
As can be seen from the third example above this scheme requires an 'Indeterminate' or 'Poorly Known' category for those species which are suspected to be threatened but for which there is little information.
In summary this or a similar scheme should be adopted to categorise freshwater fishes. However the applicability of the quantitative criteria to freshwater fishes should be investigated, and new criteria developed if necessary.