On December 22, 2006, President Bush signed P.L. 109-449 ( S. 362 ), establishing NOAA and Coast Guard programs to manage marine debris and address its adverse effects on endangered species. On December 9, 2006, the Senate agreed to the House-amended S. 362 . On December 9, 2006, the House passed the Senate-amended H.R. 5946 . On December 7, 2006, the Senate passed H.R. 5946 , amended to incorporate language (1) requiring a study of sea turtle excluder devices in shrimp trawls, and (2) implementing the Agreement on the Conservation and Management of the Alaska-Chukotka Polar Bear Population. On December 6, 2006, the Senate passed H.R. 4075 , after amending this bill to incorporate language implementing the Agreement on the Conservation and Management of the Alaska-Chukotka Polar Bear Population. (This report replaces CRS Issue Brief IB10144, The Endangered Species Act (ESA) in the 109 th Congress: Conflicting Values and Difficult Choices , by [author name scrubbed] et al.) The 1973 ESA ( P.L. 93-205 , as amended; 16 U.S.C. §§1531-1543) was a comprehensive attempt to protect species at risk of extinction and to consider habitat protection as an integral part of that effort. A stated purpose of the ESA is to protect the ecosystems of which listed species are a part. Under the ESA, species of plants and animals (both vertebrate and invertebrate) may be listed as either endangered or threatened according to assessments of the risk of their extinction. More flexible management can be provided for species listed as threatened. Distinct population segments may also be listed as threatened or endangered, but only of vertebrate species. Consequently, some populations of chinook, coho, chum, and sockeye salmon in Washington, Oregon, Idaho, and California are protected under the ESA, even as other healthy populations of these same species in Alaska are not listed and may be commercially harvested. More limited protection is available for plant species under the ESA. Once a species is listed, powerful legal tools, including penalties and citizen suits, are available to aid species recovery and protect habitat. Use of these tools, or the failure to use them, has led to conflict. The ESA is administered by the Department of the Interior's Fish and Wildlife Service (FWS) for terrestrial and freshwater species and some marine mammals, and by the National Marine Fisheries Service (NMFS; also popularly referred to as NOAA Fisheries) in the Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) for the remaining marine and anadromous species. The U.S. Geological Survey's Biological Resources Division conducts research on species for which FWS has management authority; NMFS conducts research on the species for which it is responsible. As of September 20, 2006, a total of 1,132 species of animals and 747 species of plants had been listed as either endangered or threatened, of which the majority (567 species of animals and 744 species of plants) occur in the United States and its territories and the remainder only in other countries. Of the 1,311 U.S. species (an increase of 49 species since December 31, 2002), 1,070 are covered in recovery plans (an increase of 70 species since December 31, 2002). Of the U.S. species, 475 have designated critical habitat (CH) in some portion of their range. At times, efforts to protect and recover listed species are controversial; declining species often function like the proverbial canary in the coal mine, by flagging larger issues of resource scarcity and altered ecosystems. Past resource debates in which ESA-listed species were part of larger issues include Tennessee's Tellico Dam (water storage and construction jobs versus farmland protection and tribal graves, as well as snail darters); Pacific northwest timber harvest (protection of logging jobs and communities versus commercial and sport fishing, recreation, and ecosystem protection, as well as salmon and spotted owls); and Texas's Edwards Aquifer (allocation of water among various users with differing short- and long-term interests, as well as several spring-dependent species). Species may be listed on the initiative of the appropriate Secretary or by petition from an individual, group, or state agency. The Secretary must decide whether to list the species based only on the best available scientific and commercial information, after an extensive series of procedural steps to ensure public participation and the collection of scientific information. In deciding whether a species needs the protections of the ESA, the Secretary may not take into account the economic effects that listing may have; economic and other considerations are taken into account in structuring alternatives for assisting the species after listing. In addition, FWS and NMFS may identify selected species by adding them to a list of "candidate species" believed at sufficient risk to warrant protection, but such protection is precluded by work to protect listed species. As of September 13, 2006, there were 279 species on the list of candidate species. With certain exceptions, if a species is listed, the Secretary must designate critical habitat (CH) in areas where the species is currently found or which might provide additional habitat for the species' recovery. However, if the publication of this information is not prudent (e.g., might encourage vandals or collectors), the Secretary may decide not to designate CH. The Secretary may postpone designation for up to one year after listing, if the information is not determinable (16 U.S.C. §1533). As of June 16, 2006, FWS had designated CH for 36% of listed domestic species. As a practical matter, CH has not been designated for most listed species largely because FWS prefers to allocate its limited resources to listing new species, based on its regulation (50 C.F.R. §402.02) that takes away much of the legal value of designating CH to the recovery of the species. Yet FWS consistently loses legal challenges for failure to designate CH, and several courts have found the regulation in question to be an erroneous interpretation of the law, because it does not take into account the duty to avoid adverse modification of CH. Others have asserted the value of CH; for example, scientists with the Center for Biological Diversity published a study in April 2005, concluding that CH designation enhances species recovery. On April 28, 2006, the Keystone Center's ESA Working Group on Habitat released a report on habitat protection and the ESA. One of the conclusions of participants in this study was that identification of the habitat that species require to recover is better done in the context of recovery planning, after more rigorous analysis and deliberation have been completed, rather than at the time of listing. CH is frequently misunderstood by the public as posing a significant direct restriction on private landowners' authority to manage land. While a landowner may experience some additional procedures and possible restrictions on land management because of the presence of an ESA-listed species (through the ESA's prohibitions on taking a listed species), and the presence of CH may shed light on whether "harm" has occurred, the duty to avoid adverse modification of CH is an express obligation only for federal agencies and actions, or private (nonfederal) actors in actions with a federal nexus (i.e., actions that involve any federal funding, permit, or license). (See also " Issues in the 109 th Congress ," below.) The ESA contains prohibitions on the "take" of endangered species; take means to "harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect or attempt to engage in any such conduct" (16 U.S.C. §1532; harassment and harm are further defined in regulation at 50 C.F.R. §17.3). There has been controversy over the extent to which habitat modification is prohibited. A 1995 Supreme Court decision held that the inclusion of significant habitat modification was a reasonable interpretation of the term "harm" in the ESA. The ESA provides civil and criminal penalties for violations. Proposed actions that may have adverse impacts on listed species may be permitted in two ways. First, under §7 of the ESA, if federal agency actions (or actions of a nonfederal party that require an agency's approval, permit, or funding) may affect a listed species, the federal agency must ensure that those actions are "not likely to jeopardize the continued existence" of any endangered or threatened species, nor to destroy or adversely modify CH. To review the possible effects of their actions on listed species and CH, federal agencies must consult with the appropriate Secretary. If the Secretary finds that an action would jeopardize a listed species or destroy or adversely modify CH, the Secretary must suggest reasonable and prudent alternatives that would avoid these harms. Pending completion of the consultation process, agencies may not make irretrievable commitments of resources that would foreclose any alternatives. The Secretary issues a written statement, called a biological opinion , that may allow the agency or the applicant to take individuals of a species incidental to otherwise lawful activities without triggering the ESA's penalties, subject to terms and conditions specified in the opinion (16 U.S.C. §1536), or may conclude that jeopardy cannot be avoided, in which case the agency may seek an exemption for the action from the Endangered Species Committee. For actions without a federal nexus (i.e., no federal funding, permit, or license), the appropriate Secretary may issue permits under §10 of the ESA to allow the incidental take of species during otherwise lawful actions.