Many situations have focused congressional attention on the adequacy of the science supporting implementation of the Endangered Species Act (ESA). While most science-based actions under ESA are unchallenged, opponents of some actions under ESA accuse agencies of using "junk science," while others assert that decisions that should rest on science are instead being dictated by political concerns. Legislation to address the use of science in implementing ESA has been introduced in each Congress since the 107 th Congress, but no measures have been enacted. The ESA was enacted to identify species at risk of extinction, to provide means to help such species recover, and to protect the ecosystems of which declining species are a part. Listings and other actions under the ESA may affect land uses and development. Endangered species are likely to reflect stressed resources or ecosystems, with various interests on all sides of the resource issues. There are multiple examples, such as protecting salmon in the Klamath River Basin or northern spotted owl habitat in the Pacific Northwest, where economic and social disputes have resulted from actions taken to list, protect, and recover species under the ESA. As a result, the protective posture of the ESA and the use of science in its implementation have received renewed attention. By law, ESA decisions must be based on the best science available, but this requirement can mean different things to different people. The agencies that administer the ESA, the Fish and Wildlife Service (FWS) in the Department of the Interior, and the National Marine Fisheries Service (NMFS) in the Department of Commerce, have procedures and policies in place to ensure the objectivity and integrity of the science that underpins agency decisions. In addition, the Information Quality Act (IQA) resulted in guidelines from the Office of Management and Budget (OMB) in 2001 that also relate to the quality of agency information. The agencies have responded to the IQA with additional ESA-related guidelines, and FWS, like the rest of the Department of the Interior, has adopted a new Scientific Integrity Policy. At issue has been how science is used in the ESA processes for listing species, consulting on federal actions, designating critical habitat, and developing recovery plans. For example, oversight hearings have focused on whether more scientific rigor is necessary in implementing the ESA. A later hearing concerned DOI efforts to avoid more instances of documented modification of scientific conclusions through political manipulations by senior officials. Beginning with the 107 th Congress, bills have been introduced to require empirical or field-tested data as well as independent scientific reviews, science review boards, and increased public involvement. Questions have also been raised on how to handle situations when the available science is not extensive. Some suggest that considerations other than species conservation should prevail; others seek to change the current posture of the law by changing the role of science. For still others, efforts to amend the ESA in these areas are seen as an attempt to undermine the ESA, which they assert struck a reasonable balance on these issues, and they question whether an amendment concerning science is advisable or practical. These considerations are complicated by the costs and time required to acquire more extensive data, particularly in connection with many lesser-known species. Many rare and endangered species are little studied because they are hard to find or because it is difficult to locate enough of them to support scientific research. In addition, restrictions on activities that might affect listed species could discourage some research. This report approaches the issues surrounding "sound science" by discussing (1) controversies over the last decade; (2) the role of science in general—what science is, and what it can and cannot do—as background for assessing the adequacy of science in ESA implementation; (3) the role of science in the legal and policy ESA context; (4) current requirements on the quality and use of information and science by FWS and NMFS; and (5) legislation to address concerns relating to ESA science. Several situations have focused congressional attention on concerns about the adequacy of ESA science. Examples illustrating a range of different types of scientific concerns include (1) allegations of sample tampering in population surveys for Canada lynx; (2) concerns over how to treat surplus hatchery-propagated salmon; (3) Steller sea lion protection and its conflicts with North Pacific fishery management; and (4) eastern gray wolves. Before the Canada lynx ( Lynx canadensis ) was listed in 2000, a federal interagency group began a three-year nationwide survey of habitat in 1999 to detect the presence or absence of Canada lynx, a species then under consideration for ESA listing. This survey annually covered more than 60 sampling areas in several states. Hair samples were collected and analyzed for DNA characteristics to identify the species that left hair samples on rubbing posts. A positive result (i.e., a "hit") of a lynx hair sample in an area already known to be occupied lynx habitat was used to help calibrate survey effectiveness. If a hit came from habitat where lynx occupancy was unknown, tracking surveys in snow and other investigations were conducted to verify the hit. These tracking surveys and associated investigations were intended to help determine the extent and significance of lynx occurrence in the area. A conclusion that wild, resident lynx were present was not automatically made from survey hit information, since the hit could also be from feral lynx (e.g., an escapee from a lynx fur farm), pet lynx, or wild but transient lynx. Controversy arose from media reports of possible irregularities with the collection and testing of lynx survey samples. Several federal and state researchers had submitted hair samples for testing which had not been collected naturally from the wild, to test the capability of the testing procedures. These submissions were not in the planned protocol for the studies. Some individuals feared that unplanned test samples might be used to extend the known range of ESA-protected lynx and impose additional restrictions on land owners. Concerns were also raised that media coverage may have sensationalized the situation beyond its facts. No new habitat was added to the lynx's known range as a result of the irregular samples. Another issue regarding listing of lynx illustrates the difficulty of studying and listing rare or elusive species whose ranges and behaviors are not well understood. With the original listing, no lynx in New Mexico were covered, because FWS did not include states where the population was thought to be transient, or not viable due to an inadequate prey base—in the New Mexico case, too few snowshoe hares. However, further research showed that perhaps lynx were more abundant there than previously thought. On August 8, 2007, Forest Guardians, Sinapu, Center for Native Ecosystems, Animal Protection Institute, Animal Protection of New Mexico, Carson Forest Watch, and Sierra Club, Rio Grande Chapter, petitioned to have the listing changed to include portions of northern New Mexico. One major issue in the boundary change debate was whether any lynx found in northern New Mexico were simply young, dispersing animals that would eventually die out after being unable to find adequate resources or whether these young animals represented a significant part of the population. Eventually, FWS concluded that this portion of the species' range warranted inclusion in the listing, but that the change was precluded by other higher priorities. It assigned the listing decision a priority of 12, the least urgent possible level. Designation of critical habitat for this species has also been controversial on scientific grounds. Defenders of Wildlife sued FWS to force designation of critical habitat. The U.S. District Court for the District of Columbia instructed FWS to propose critical habitat by November 1, 2005, and to issue a final rule for critical habitat by November 1, 2006. On November 9, 2006, FWS designated approximately 1,841 square miles of critical habitat in three states: Minnesota (Koochiching and St. Louis counties), Montana (Flathead and Glacier counties), and Washington (Chelan county). Because boundaries within the chosen states were primarily national parks or other protected areas, and because other states with lynx habitats were omitted, some environmental and scientific groups charged that even these boundaries were inadequate, and another suit was filed to expand designated critical habitat. Among other things, these groups argued that the designation was inadequate on various scientific grounds. On February 25, 2009, FWS determined that the critical habitat should be expanded to approximately 39,000 square miles in portions of Maine, Minnesota, western Montana, northeastern Idaho, north-central Washington, and northwestern Wyoming. FWS also acknowledged that a former deputy assistant secretary at the Department of the Interior, Julie MacDonald, may have inappropriately reduced the earlier designation. The 2009 critical habitat designation was ruled invalid by the Montana federal district court, which found that FWS had not considered the economic impacts adequately. The court halted application of the critical habitat designation in the area in which the economic analysis had been inadequate (a national forest in Washington). An earlier decision, by a different judge of the same court, also found the critical habitat designation flawed, but left the rule in place while FWS considered the features of lynx-occupied areas in certain national forests. Naturally spawned fish are genetically diverse and therefore considered to be more vigorous than the genetically more similar hatchery fish. Consequently, agency scientists have distinguished between hatchery-raised and wild salmon to maximize production of the latter. Over the years, these distinctions have been controversial in several respects. In 1993 NMFS issued its Interim Hatchery Listing Policy on how to consider hatchery fish in listing determinations for Pacific salmon and steelhead species. The interim policy concluded that hatchery fish could be in the same evolutionarily significant unit (ESU) as wild fish. Eventually, a federal court found that the interim policy violated the ESA by listing below the species level.