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

concordance in their descriptions of the eiders’ decline. Neither of the two most precise
surveys (one aerial, one ground-based), however, were designed specifically to monitor
numbers ofSpectacled Eiders. Manipulation of these databases to include inter-survey
comparisons and restratification may lead to survey modifications that will yield a more
precise estimate of the breeding population and its trend.
With the exception ofa small data set from the Prudhoe Bay oil fields and traditional
ecological knowledge from Wainwrigbt, no trend data exist for Spectacled Eider
populations on the NS or in AR. Further, with the exception of a crude estimate from the
Indigirka Delta, there are no estimates of historical population sizes in either of these two
regions. Accurate and precise estimates of sizes and trends of populations will be needed
for evaluating whether or not these populations meet the criteria for reclassification.
Therefore, it is important that recently-initiated survey efforts on the NS and in AR be
continued and enhanced with consideration of the effort needed to obtain the precision
achieved on the YKD. For all surveys, a power analysis should be conducted. In other
words, the probability of detecting a true change in population size must be determined,
and surveys should be refined accordingly to improve preclslon.
c. Population Dynamics--Although trend data can indicate the overall response of a
population to its environment, such data alone can neither illuminate the causes for such
responses nor predict the probabilities of specific responses in the future. Questions
concerning population dynamics fall within the scope ofpopulation modeling and
demographics.
Among various types of population models, population viability analysis (PVA) has
become almost d~ rigour in recovery planning for endangered species. PVA can generate
estimates for minimum viable population sizes at varying levels of risk (i.e., probabilities
oflong-term persistence). PVA has limitations, however, and such an approach is not
necessarily appropriate in all circumstances. Specifically, it is inappropriate to use
demographic data from a declining population (such as the Spectacled Eider population on
the YKD) to conduct a PVA.
As an exercise, however, PVA can help to guide decisions about research priorities and
recovery criteria. Population modeling, including PVA, will be a central aspect of
Spectacled Eider recovery planning, both during and beyond the exploratory phase of data
collection. Initially, this modeling will highlight critical data gaps. Then, as life history
data accumulate, the models should become increasingly robust and predictive and, thus,
should allow evaluation of hypotheses addressing the cause(s) of the eiders’ decline and
assessing obstacles to recovery. In addition, some models may help us assess the urgency
of required actions if populations slip toward extinction. For stable or growing
populations, minimum viable population models should allow us to estimate the time
needed for recovery, and, for planning purposes, the cost of that recovery.
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