A. Status of the Spectacled Eider - U.S. Fish and Wildlife Service

thresholds are not “magic numbers” that guarantee extinction or recovery. Instead, these
thresholds serve as mileposts that identify populations at high risk and measure progress at
reducing that risk.
For example, the World Conservation Union (International Union for the Conservation of
Nature [IUGNI)has suggested risk levels (i.e., thresholds) for classifying species (see
Appendix I). The Service considered the IUCN criteria as guidelines in developing the
reclassification criteria for Spectacled Eiders. Specificafly, the IUCN has identified a
population level of 125 pairs as critically endangered, and the population models in Appendix I
of this plan use 125 pairs as a benchmark for assessing the risk of extinction.
There is no particular biological significance to the exact number chosen for the “critical”
population size. The value could just have easily been 150 or 100. Despite the somewhat
arbitrary nature of the number, however, such a figure has both heuristic and practical
applications. Consider a population of 2,000 pairs (roughly the size ofthe Spectacled Eider
population on the YKD in 1994). If the population declines at a rate of 5%/year, extinction is
over a century away, but the population will spend nearly half of the next 100 years at
numbers less than 125 pairs (Figure 11). Thus, the extinction time gives an overly optimistic
picture of how much time remains for conservation action to be implemented effectively. In
other words, in most cases, once a population falls below abQut 125 pairs, only the most
radical conservation efforts will result in its full recovery. The critical population size,
therefore, is used as a practical baseline to estimate the time remaining for constructive
research and recovery actions.
The reclassification criteria presented below should be viewed in the same light. Passing a
specific population threshold defined in this plan neither seals the fate ofdeclining populations
nor secures the future for increasing populations. Rather than defining biological failsafe
points, the criteria identify thresholds at which the Service’s level ofconcern about a
population changes. The calculations in the appendices provide a quantitative framework of
objectivity for what are, ultimately, subjective decisions. By indicating when different levels
of protection are required, the criteria represent the Service’s most prudent assessment of a
population’s risk.
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