Our third criterion involves using
a 50-year rule as an insurance policy (albeit arbitrary) against prematurely
declaring a species "extinct;" in other words, unless at least 50 years
have passed since the species was last located in the wild, its extinction
cannot be declared "resolved." We adopted this protocol because it provides
a lengthy time period during which the species, if still extant, might
be seen or collected, purely by chance. This can be particularly important
when it is difficult to judge whether sufficient sampling has been conducted
to confirm the species' absence.
What is your opinion of the 50-year
rule? (Realize that this rule in no way precludes listing species that
are most likely extinct - it merely puts them in a different category
to indicate that the species has met other criteria except for the 50-year
rule.) Would you alter this time span or eliminate it altogether? If eliminated,
how would you deal with the possibility that:
(1) the species is particularly
difficult to collect regardless of sampling-- for example, because it
is cryptic or naturally rare.
(2) the habitat is particularly
difficult to survey -- for example, marine environments.
(3) the species is temporally
absent from its typical habitat, but not extinct; for example, when environmental
change or ecological shift result in the movement of the species to a
different, unexpected (and unsurveyed) habitat.
Comments by CREO Chairman,
Ian Harrison, have been added to some of the responses below -- in underlined
Amphibians Advisory Panel
Comment 1: 50
year rule is generally acceptable for amphibians. Many are cryptic in
Comment 2: 50 year
rule is generally acceptable for animals. Plants, with seeds that
can stay dormant for long periods of time, are a problem.
Comment 3: 50 years
is adequate for an organism that has taken several years to reach
sexual maturity. But if a species reaches sexual maturity within one
year, 50 generations is too long. Maybe we need a new category of
Comment 4: 50 years
is practical -- but one problem is that in many biodiversity-rich
developing countries no recent surveys have been made. Many species
that are known from old names/specimens have not been surveyed in
over 50 years and so could be declared extinct based on this lack
of information (this indicates that even a 50 year rule does not
solve the problem of dealing with species from inaccessible and unsurveyed
areas; thus, the 50 year rule probably should not be used alone for
resolving an extinction; surveying evidence is also required).
Birds Advisory Panel
Comment 1: 50
year rule is acceptable by weight of convention and utility - but one
should recognize that the 50 year rule is not proof of extinction.
(The rule should be implemeted with other criteria, as discussed
in Harrison & Stiassny's (1999) fish paper).
Comment 2: 50 year
rule is problematic. IUCN requires published evidence of sampling
across space and time that is equivalent to the species life-history.
Waiting 50 years may be redundant in some circumstances - the term
"Provisionally extinct" or Apparently Extinct" could be applied in
such circumstances. In other cases there may be habitats that are
too inaccessible to sample and so a species could meet the 50 year
rule simply through lack of sampling - "to have a criterion which
is so unsophisticated that taxa endemic to unvisited places get listed
as extinct would not be helpful. So this needs work.
Comment 3: 50 years
was just sufficient for the takahe [1898-1948]. There must be a cut-off
date and 50 years is as good as any. There will always be exceptions
to whatever date is applied. For some groups, 100 years will not allow
enough time for certainty, eg. McGillinays (?) petrel and the
Chatham island taiko.
Comment 4: the 50
year rule is a reasonable one generally, but clearly it will prove
too short for some cryptic and/or potentially widespread species."
(So if it is to be used it must be applied in conjunction with
Coleoptera Advisory Panel
Comment 1: the
50 year rule is a conservative approach. As for species that may be
rare or difficult to sample, this is an issue that persistently affects
listing decisions in the US. Where there is reason to suspect that a
particular organism may simply be difficult to collect (eg. , moths
not attracted to black light traps) the 50 year rule should probably
be suspended pending at least some attempt to locate an extant population
according to whatever methods are available. These issues are best addressed
by recourse to experts familiar with the biology of the organisms in
Comment 2: a 50 year
rule has been used in a case of a putative extinction of a Hawaiian
carabid beetle. A 100 year rule will of course give more confidence
of loss than a 50 year rule (just as one would find by using different
p-values for estimating statistical significance. If nobody has looked
for the species in 100 years then that should also be revealed; ie.
sampling should be rigorous.
Comment 3: the
rationale for the 50 year rule seems a good one, in general principles.
Comment 3: this is
OK for plants or vertebrates, and also probably OK for some lepidoptera.
We might need to be more flexible for beetles.
Fishes Advisory Panel
Comment 1: there
are cases where the 50 year rule seems unnecessary to justify an obvious
extinction, such as extinctions in cities where habitats are totally
destroyed; whereas in other cases such as the Amazon the extinction
is much less definitive and so the 50 year rule may be more helpful.
However, the 50 year rule can be helpful in justifying the extinction,
but it should have some correlation to the species' life span. Also,
it happens to be related with the latest activities after the World
Comment 2: 50-year
rule may be OK for deep sea fishes or species inhabiting large rivers,
or forest insects etc. But in the case of species restricted to a
single spring in a desert (e.g. Mexican pupfishes), if the spring
dries out for a few years then it seems that the case should be declared
resolved much faster. Waiting for 50 years in such obvious cases is
counter-productive because it creates the possibility that people
will talk about obvious extinctions when CREO still do not list them
as resolved. So it creates a lack of trust in who to believe; this
is a serious problem when we want to use known cases as examples of
what will happen in areas to be impacted by new projects. Although
there is a need for some suitable waiting period before declaring
a species extinct, it may not be sensible to call a species 'probably-extinct'
for 50 years: such semantic subtleties can be used as an argument
for not doing anything. Perhaps the definition of the requisite waiting
period should allow for different periods for different categories,
habitats, habits, areas (although this is against the justified, advocated
aim of having criteria applicable across taxa). The wording of a rule
for a suitable waiting period should be correctly selected, not only
to reflect the truth, but also to prevent misuse or semantic distortion.
Comment 3: 50 year
rule seems logical. For example, if the Comoros islands population
of the coelacanth had become extirpated a few years ago, it might
have seemed logical to assume the species was extinct if no 50 year
rule was applied; but recent discovery of the Indonesian population
would have shown this to be wrong. This example also underscores some
significant problems in evaluating species from a vast environment
like the ocean. (The marine example shows a very real reason
for a 50 year rule, to give an opportunity to find a species in an
extensive environment; but it also shows that just because the 50
year rule is met the species is not necessarily extinct, because the
environment might be too large to cover in 50 years. Panelists for
mammals have also addressed this problem, stating that sampling and
decisions of extinction should be weighted according to the size of
their environment; this is very sensible in theory, but it may be
more difficult to apply practically?).
Lepidoptera Advisory Panel
Comment 1: while
there are valid reasons for adopting the 50 year rule, in practice
there is little functional relevance to this rule for lepidoptera.
Because of rapid generation times, and high variability in abundance
and apparency of many Lepidoptera in successsive seasons, such hard
and fast lines are unwise. Extinctions may be detected much more rapidly,
and it would be better to have greater flexibility here for such shortlived
has warned against use of 50 year type rules when sampling is not
evident; insects can show enormous changes in population numbers so
may be apparently absent for some decades before re-appearing).
Mammals Advisory Panel
Comment 1: 50
year rule is useful for species that are easily detected, but not good
for species that are easily overlooked or are in habitats that are difficult
to sample. In these cases it must be associated with other criteria
to test for evidence of presence or absence of the species. (Fish
Panelists stated exactly the opposite - the 50 year rule seems unecessary
where the species can easily be located, because there is no reason
to assume that it might be present but not detected. However, the comment
made here is valid: when species are typically difficult to locate then
one should not assume that, just because they have not been seen for
50 years, they are therefore extinct. The 50 year rule must be backed
up by indication of sampling etc. in these circumstances).
Comment 2: 50 year
rule is not acceptable; several Australian mammal extinctions are
undisputed but have occurred within the last 50 years.
Comment 3: 50 year
rule is very problematic. The species might not be directly studied
because no money is available (however, in these circumstances,
the 50 year rule may provide a safety net for an otherwise overlooked
species, ie. it is seen by chance despite a lack of intense sampling.
If the species is not seen, then the rule must be applied in conjunction
with some indication of level of sampling, to reduce the chance of
incorrectly listing the species as extinct, as noted above). But
the rule may also preclude the inclusion of a species that is probably
extinct. Perhaps the time can be reduced.
Comment 4: supports
the 50 year rule.
Molluscs Advisory Panel
Comment 1: This
may be OK in the case of widely distributed taxa. There are many highly
localized taxa where verification of extinction can be achieved readily.
Rules should be flexible enough to take this into account. If a specialist
panel for the group in question thought that the 50 year rule was necessary
to apply in a particular case, then the rule should be accepted in this
case. However, many mollusk species would not have been collected over
a fifty year period simply because no one has done it.
Reptiles Advisory Panel
Comment 1: this
is significant problem because reptiles and species not seen or collected
for over 100 years are "rediscovered" with some regularity. The 50 year
rule should be retained in cases of species occurring in areas/habitats
that have adequate sampling or at least reasonably frequent visits by
specialists. A 100 year rule might be more appropriate for remote or
inaccessible areas. Alternatively, 25 years may be acceptable in cases
in which all appropriate habitat has been destroyed or the distribution
is known to have been very restricted.
Comment 2: some form
of annotation on the list that a species has not been searched for
in appropriate habitats/within the known range of the species; or
XX man-hours/weeks/months spent in species-directed searches etc.
(Some quantification of effort of sampling would be very informative;
I think it will be difficult to develop a quantitative measure that
can be consistently and accurately to fieldwork for diverse taxa.
However, even simply noting the number of times fieldwork has been
reporting for a particular area might help. This should be covered
in the additional criteria discussed below).
Comment 3: 50 year
rule is acceptable
Comment 4: the 50-year
rule is good enough to estimate extinctions if the species corresponds
to the possibilities (1), (2), and (3) above. A 50 year period is
reasonable for most species of reptiles, even cryptic species.
Comment 5: the 50
year rule seems reasonable, especially given that this rule does not
preclude listing species that are most likely extinct - it merely
puts them in a different category to indicate that the species has
met other criteria except for the 50-year rule. For example some species
that have a very limited distribution can with some degree of accuracy
be listed as extinct if not recorded/collected under the 50 year rule.
The best option would be to allow exceptions to the 50 year rule,
using your examples 1-3 above.