Polar Bear

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III. Management Goals and Criteria USFWS E. The Population Dynamics of Conservation, Recovery, and Harvest If we are successful in achieving the criteria described in this Plan, what will conservation and recovery of polar bears look like? The conservation criteria under the MMPA and the recovery criteria under the ESA are not stated in terms of desired population sizes, because conservation and recovery could be achieved at different population levels. Instead, the criteria are stated in terms of demographic processes (e.g., persistence, survival, reproduction, carrying capacity, anthropogenic mortality) that link back to the fundamental goals for polar bears, several of which were framed in terms of probability of persistence. The concepts behind the demographic processes may be unfamiliar to some readers, so it is fair to ask, what would conservation and recovery look like? Why do all of these criteria add up to fulfillment of the obligations under MMPA and ESA? And how is it that harvest can be compatible with conservation and recovery? A picture of conservation As described above, the proposed MMPA criteria seek two things: to maintain the health and stability of the marine ecosystem, as reflected in the intrinsic growth rate and carrying capacity for polar bears, above a certain level; and to maintain each polar bear subpopulation above its maximum net productivity level. The first MMPA criterion indicates that there is a limit to the loss of carrying capacity that can occur before the stability of the marine ecosystem is lost and polar bears would cease to be a significant functioning element of the ecosystem (Fig. 6, scenario 1). The threshold described in this Plan indicates that a substantial portion (70%) of the historical carrying capacity must be maintained (where “historical” carrying capacity refers to the carrying capacity in the decades preceding enactment of the MMPA). If a declining carrying capacity Key Terms Carrying capacity. The size at which a population would stabilize if there were no direct anthropogenic removals. The carrying capacity can change over time, if the underlying habitat changes. Stable ecosystem threshold. The threshold for carrying capacity identified in MMPA Conservation Criterion 1 below which the stability of the marine ecosystem is unacceptably altered. Intrinsic growth rate. The population growth rate in the absence of anthropogenic removals and at low density. This is the potential growth rate, not the observed growth rate, and is an important measure of the resilience of a population. Maximum net productivity level. The population size at which the net growth in the population (births minus non-anthropogenic deaths) is greatest. Under the interpretation used in this Plan, mnpl changes in proportion to carrying capacity. Quasi-extinction floor. The threshold for evaluating “extinction” under the ESA in this Plan. Rather than use outright extinction as the condition to be avoided, we are using a more conservative definition that avoids the conditions that might give rise to an unavoidable downward spiral. If a population crosses below this threshold, it has ceased to persist, for purposes of assessment under the ESA. 34 Polar Bear Conservation Management Plan
III. Management Goals and Criteria Subpopulation Size Subpopulation Size 1 Time 1 Time Subpopulation Size Scenario 1 2 3 Carrying Capacity (K) Population Size MNPL Stable Ecosystem Floor Time 1 Figure 6. Achieving the MMPA conservation criteria requires keeping carrying capacity above the stable ecosystem threshold, and keeping the population between mnpl and carrying capacity. Scenario 1 (red) shows the trend over time of a subpopulation with well-managed take, but in an ecosystem that loses nearly all capacity to support polar bears; this is the expectation for polar bears in most subpopulations if the threat of climate change is not abated. Scenario 2 (purple) shows the trend over time of a subpopulation with unsustainable levels of take, which cause the population size to decline below mnpl and may decrease population viability. Scenario 3 (green) shows the trend over time of a subpopulation with well-managed take and an ecosystem that stabilizes before it reaches the point at which the health and stability are lost, even though a portion of the original carrying capacity is lost. The black line in scenario 3 provides a reference to the carrying capacity in the absence of an anthropogenic effect on polar bear habitat. This figure is a simplification for the purpose of illustration; assessment of the criteria will also need to take into account annual variation, precision of estimates, and other considerations. stabilizes and is expected to remain stabilized above the threshold associated with a stable ecosystem, then the first criterion is met (Fig. 6, scenario 3). This criterion does not require that the historical carrying capacity (Fig. 6, scenario 3, black line) be maintained, but rather that the decrease in carrying capacity is limited and ultimately stabilized; the historical carrying capacity is nevertheless a valuable reference point for understanding the extent of decrease in carrying capacity and associated ecosystem stability. Note that the first criterion concerns the carrying capacity, not the population size (which may be below the carrying capacity because of human-caused removals); if the population size drops below the threshold, but the carrying capacity does not, the criterion is still met, although some thoughtful consideration of the level of take might be prompted. In the absence of global Polar Bear Conservation Management Plan 35
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Page 5 and 6: Contents Executive Summary.........
Page 7 and 8: Executive Summary Today, polar bear
Page 9 and 10: and connectivity in each recovery u
Page 11 and 12: I. Background I. BACKGROUND Polar b
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Page 61 and 62: VI. Glossary Population. A group of
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Appendix A—Background Lunn, N.J.,
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Appendix A—Background Rode, K.D.,
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Appendix A—Background Voorhees, H
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Appendix B—Specific Conservation
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