The act sets forth what's required in designating an area as "critical habitat," but it also specifies possible exclusions. The Secretary of the Interior, says the act, "shall designate critical habitat, and make revisions thereto, . . . on the basis of the best scientific data available and after taking into consideration the economic impact, the impact on national security, and any other relevant impact, of specifying any particular area as critical habitat. The Secretary may exclude any area from critical habitat if he determines that the benefits of such exclusion outweigh the benefits of specifying such area as part of the critical habitat, unless he determines, based on the best scientific and commercial data available, that the failure to designate such area as critical habitat will result in the extinction of the species concerned."
Furthermore, the Secretary of the Interior "shall develop and implement plans (hereinafter in this subsection referred to as 'recovery plan') for the conservation and survival of endangered species and threatened species listed pursuant to this section, unless he finds that such a plan will not promote the conservation of the species. The Secretary, in developing and implementing recovery plans, shall, to the maximum extent practicable . . . give priority to those endangered species or threatened species, without regard to taxonomic classification, that are most likely to benefit from such plans, particularly those species that are, or may be, in conflict with construction or other development projects or other forms of economic activity; The full text of the act may be found at http://www.fws.gov/Endangered/esa.html.