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

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Trend data are analyzed to inform wildlife managers about the risks faced by populations. As noted above, however, the uncertainty in abundance and trend data can lead to errors of interpretation and, therefore, decision-making. In terms of threatened and endangered species classifications, two possible errors might occur: 1) failing to classify a threatened or endangered population that should be classified (the under-protective error); and 2) classifying a population as threatened or endangered when it should not be classified (the over-protective error). The decision about when to classify a species to a specific risk category depends on the costs of making the over- or under-protective errors. We analyze the eider trend data using Bayesian statistics, which allows us to directly incorporate the costs of errors into the decisionmaking framework. For the purposes of this analysis, the team considered the costs of committing under- or over-protective errors to be equal. Bayesian analysis results in a probability distribution for population growth rate (r) given all the available data and uncertainty about the variability in population growth rate (Taylor et al. in press). We can therefore answer such questions as “What is the probability that this population was experiencing a decline of ~5%/year when these data were gathered?” Before using such a probability distribution (called a posterior distribution in Bayesian statistics) in decision making, we must specify the costs of committing errors. If we erroneously fail to classify a population declining at 5%/year, it is a more serious mistake than failing to classify a population declining at 1 %/year. Indeed, we have just noted that species should be classified by the level of risk and the level ofrisk increases with increasing rate of decline. Bayesians call the costs at different values of r (population growth rate) “loss functions” (Figure 9, details in Appendix II). References to “loss” and “loss functions” in the following discussion refer to the costs of making incorrect management decisions and should not be confused with loss ofbirds (i.e. a population decline). The cost of making decision errors (loss functions) is measured in terms of the probability of decreasing to under 250 adults in 50 years. Thus, the loss functions are in units that reflect the consequences of the management decision. The time required to determine the cause of decline and attempt to reverse was estimated by the recovery team to be about 50 years. A population of 250 adults was chosen as the point when prudent management action is reduced to the single alternative of captive breeding. A decision with high risk is one which has a greater likelihood of resulting in the population decreasing to under 250 adults in 50 years. A decision with low risk is one which has less likelihood of resulting in the population decreasing to under 250 adults in 50 years. In Figure 9, the loss function with filled square symbols gives the loss ofnot classifying the population for different population growth rates (the underprotection error). Clearly, there is no loss when the population is stable or growing (r =0) because the correct decision was made. Similarly, if the decision threshold to classify as endangered is r = -0.05, then the loss if the decision is to classify is zero when r =-0.05 because the correct decision was made. The decision to equalize over and under-protection errors makes these functions symmetrical around r = -0.025. 30
Figure 9. Loss functions for the under-protection error (failure to classify) in filled squares and the over-protection error (falsely classifying) in open squares. Risk is measured as the probability of becoming critical (
Page 2 and 3: SPECTACLED EIDER RECOVERY PLAN Team
Page 4 and 5: LITERATURE CITATION U.S. Fish and W
Page 6 and 7: EXECUTIVE SUMMARY OF THE RECOVERY P
Page 8 and 9: TABLE OF CONTENTS DISCLAIMER PAGE 1
Page 10 and 11: LIST OF FIGURES Figure 1. Breeding
Page 12 and 13: A. Status of the Spectacled Eider R
Page 14 and 15: ) a) j~ 25000 0 2 220000 C ~15000 ~
Page 16 and 17: B. Causes for Decline and Obstacles
Page 18 and 19: Increasing interest in avicultural
Page 20 and 21: Other conservation measures include
Page 22 and 23: D. Natural History of the Spectacle
Page 24 and 25: Figure 4. Yukon-Kuskokwim Delta loc
Page 26 and 27: DEL?A RUSSIA SPECTACLED EIDER RANGE
Page 28 and 29: helicopter surveys in the Prudhoe B
Page 30 and 31: geographic populations, because imm
Page 32 and 33: Figure 8. Study sites and land stat
Page 34 and 35: their diseases (e.g., Schiller 1954
Page 36 and 37: E. Distinct Population Segments The
Page 38 and 39: A final consideration involves info
Page 42 and 43: Figure 10. A hypothetical posterior
Page 44 and 45: thresholds are not “magic numbers
Page 46 and 47: Criteria for Reclassifying from Thr
Page 48 and 49: Criteria for Delisting from Threate
Page 50 and 51: The final aspect ofSpectacled Eider
Page 52 and 53: concordance in their descriptions o
Page 54 and 55: data on both levels and effects oft
Page 56 and 57: implicated. In the absence of histo
Page 58 and 59: . - currently small size of the YKD
Page 60 and 61: implementation of the Memoranda ofA
Page 62 and 63: . take of Spectacled Eiders. In add
Page 64 and 65: . AlS. Produce a handbook summarizi
Page 66 and 67: . Bl.4. 1.3. Develop visibility cor
Page 68 and 69: B2. 1.1. Implement YKD satellite tr
Page 70 and 71: . Appendix Ill). Since epidermal ag
Page 72 and 73: . feasible if post-fledging staging
Page 74 and 75: presumed that their activities have
Page 76 and 77: contaminants within Spectacled Eide
Page 78 and 79: limited ability to withstand additi
Page 80 and 81: surface after a year and is no long
Page 82 and 83: . The reproductive stages (eggs, yo
Page 84 and 85: is inadequate to sustain “normal
Page 86 and 87: ___________ 1967. The geese of the
Page 88 and 89: Dementev, G.P., and N.A. Gladkov (e
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___________ 1 964a. Observations on
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Nelson, E.W: 1887. Report upon natu
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________ P.R. Wade, R.A. Stehn, and
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Robert M. Platte, Migratory Bird Ma
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KEY Task Duration and Costs TBD - T
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TASK 324.2 I 12.4.1 .2 PRIOR- — 2
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TASK I — [37 E12 EI.3 fTYU —PRI
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TASK PRIOR- Dj ITYU — — A12.3 2
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— TASK U — 135.2 PRIOR- TASK DE
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TASK U PRIOR- ITY U TASK DESCRIPTIO
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TASK PRIOR. U — DS.3 3 TASK DESCR
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The final risk factor is the effect
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This PVA will treat two population
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Both aerial surveys are conducted a
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0.2 0.15 -j i 4 0.1 0 -I 0.05 0.08
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emaining before the population reac
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) critical population size; and (2)
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40%. The population growth rate cri
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Table 1-2. Results of simulation wh
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Hilborn, R. and C.J. Walters. 1992.
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APPENDIX II TECHNICAL DETAILS OF TH
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The likelihood function for the par
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initial sample. Then the O~ were re
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LU ~0.8 z -J ~0.6 I-ET1 w107 480 m1
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LITERATURE CITED APPENDIX LI De la
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where x = age. The fertility rate i
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of older females: (1) older females
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RESULTS Solutions for single cause
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0.1 0.08 ~0.06 4 0 0.04 0. 0.02 0 0
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growth rate. Perhaps this can be mo
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decline, by far the fastest way to
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LITERATURE CITED APPENDIX In Bailli
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APPENDIX IV SPECTACLED EIDER RECOVE
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APPENDIX V COMMENTS RECEIVED ON DRA
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