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Weighing the options for limiting surplus animals.

The unsustainability of many animal programs managed by zoos and aquariums has brought renewed attention to unresolved questions about various management strategies. Solving the "sustainability crisis" for many species will require housing more adults and producing more offspring than there are existing spaces in accredited zoos and aquariums. Careful reproductive management is central to addressing this challenge, but opinions differ about which management strategies are best for an individual, for a species, for an institution, or for a country or region. The primary options for limiting the number of animals that would be surplus to the population are to prevent reproduction or to euthanize. However, there is much misunderstanding about methods for controlling reproduction, in particular about contraceptives and species differences in their effects. Careful weighing of all the options is called for. Lifetime Reproductive Planning may help increase breeding success through careful reproductive management but cannot eliminate production of surplus animals. Limiting reproduction does not address the problem of animals already in the population. Despite best efforts and planning, consistently hitting target numbers for a population may never be achieved. Increasing capacity provides a temporary patch when targets are exceeded, but is not a long-term solution, since each generation potentially produces even more individuals needing even more space. Welfare considerations should be included in discussions of management euthanasia and its alternatives. Such discussions will be most productive if based on full awareness of the advantages and disadvantages of all the options. Zoo Biol. 35:183-186, 2016. © 2016 Wiley Periodicals, Inc.