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The Endangered Species Act, Issues
(Released June 2004)



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The Endangered Species Act (ESA) of 1973 is the prime piece of legislation protecting species from extinction. It mandates a continually updated list of threatened species - those that are losing population - as well as endangered species - those actually facing near-term extinction. Once a species is listed, the ESA mandates a recovery plan to help that species return to a healthy population level.

It is important to place the ESA in a global context of species extinction and biodiversity loss. Biodiversity is essentially the number of plant and animal species in an area, and the way they interact. Most biologists and ecologists consider high biodiversity to indicate a healthy environment. The species in an ecosystem depend on each other as sources of food and shelter, and allow the basic ingredients of life to circulate. Species form symbiotic relationships, interacting in a complex chain. Remove one piece from this chain, and the consequences are unpredictable. An ecosystem that relies on too few species is vulnerable to disease, drought, and other forms of destruction; more species means more of a chance that some are well equipped to survive a change in the environment.

Due to habitat loss, pollution, invasive species, hunting, and other causes, numerous species are rapidly becoming extinct. Although some extinction is part of the normal process of nature, the United States Geological Survey estimates that it is occurring at 100 times the natural rate (that is, the rate at which extinction would occur without human influence); and that the rate continues to accelerate ( Following the passage of the ESA in the United States, the international community developed the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which works to preserve species around the globe. Balancing the need for economic development with the need for environmental protection, and adapting global standards to local conditions is, however, extraordinarily tricky. A survey of the United States' experience with the ESA helps illuminate many difficulties.

Although the ESA is often considered the most successful piece of environmental legislation ever passed, it remains contested and controversial, particularly on the question of balancing economic and environmental health. Critics claim that the ESA is extreme and inflexible in mandating the protection of every species regardless of other considerations. The 1970s case of the snail darter (Percina tanasi), a small fish on the Little Tennessee River that was threatened with extinction by the building of a dam, led to an amendment allowing petitions for exemption from ESA requirements. More recently, critics have questioned the science behind ESA enforcement, arguing that healthy species are placed on the protected list. Finally, the judicial costs are enormous; lawsuits from both pro-environmental and pro-growth factions add greatly to the expense of enforcing the ESA.

The first phase of implementing the Endangered Species Act involves the actual listing of a species as threatened or endangered. Many factors are involved in this decision. According to The Congressional Research Service (CRS) Issue Brief for Congress RS21264 The Endangered Species Act and Sound Science, (July 2002) "Information may range from the informal oral or anecdotal to peer reviewed scientific studies, and hence the reliability of the information can also be variable." The listing is to be based totally on scientific principles. As CRS Issue Brief RL30792, The Endangered Species Act: Consideration of Economic Factors (January 2001; April 2003) explains, "the listing stage may include facts related to a species population, habitat, distribution, etc., as well as threats to its continued survival, but must not include economic factors." Although in theory the ESA covers all species, in practice "charismatic" species with special significance and appeal, such as the Bald Eagle, receive priority.

Nevertheless, by the end of 2002, 1,072 animal species and 748 plant species had been listed, according to CRS Issue Brief IB10072 Endangered Species: Difficult Choices (June 2002; September 2003). The document further explains that, "once a species is listed, powerful legal tools, including penalties and citizen suit provisions, are available to aid the recovery of the species and the protection of its habitat." Enforcement mechanisms include a mandated impact assessment of major projects, such as highways, bridges, and dams. Pollution sources shown to directly harm the species also face regulation. Restrictions are placed on hunting, harvesting, and trade of the listed species. Finally, citizen suits are permitted for both listing and enforcement issues.

Because biologists consider habitat loss the single most important cause of extinction, it is not surprising that the ESA provides that: "if a species is listed, the appropriate Secretary must designate critical habitat (CH) areas where the species is currently found or which might provide additional habitat for the species recovery" (IB10072). What is surprising is that critical habitat has been designated for fewer than one fourth of listed species (RL30792), although CH has been allocated for one third of domestic species. This is largely due to the decision "to allocate scarce resources to the listing of new species" (IB10072), and to the difficulty of handling questions involving private land. The Fish and Wildlife Service, moreover, believes that "CH offers little protection for a [listed] species beyond that already available," and that habitat areas outside those currently occupied by the species need to be considered.

Designating critical habitat, as well as accounting for species impact in development, both require a complex balancing of environmental versus economic factors. While ideally sustainable development would allow harmonious, environmentally friendly growth patterns, in reality this has often not been the case. The original ESA mandate, that economic factors are to play no part in listing species, has been amended so that recovery plans must account for economic impact, "in the designation of critical habitat, in the process for obtaining an exemption for a particular proposed action from the prohibitions of the ESA, and in the development of the recovery plan" (RL30792). A threatened species is always threatened, but a number of paths may be taken to recovery: "This process has been analogized to making a diagnosis of whether a patient has cancer solely on medical grounds, but later considering economic factors in determining appropriate treatment once the patient has been diagnosed." However the ultimate exception to ESA enforcement, exemption, has only ever occurred for two species (RL30792).

Although the exemption process was written into law to preserve the Snail Darter, it is not one of these two species. Rather, an act of Congress allowed the completion of the Tellico Dam in 1979. The fish did not then suffer extinction, however. Populations found elsewhere, together with transplant efforts, have since lead to an upgrading of the Snail Darter's status from endangered to threatened.

A more recent case than the Snail Darter crystallizes issues of the economy versus the environment. In 1997, a drought year, irrigation from the Upper Klamath basin was restricted in order to save two endangered fish species, the shortnose sucker (Chasmistes brevirostris) and the Lost River sucker (Deltistes luxatus), resulting in severe hardship for area farmers. A subsequent report from the National Resource Council "concluded there was neither sound scientific basis for maintaining Upper Klamath Lake levels and increased river flows as recommended in those biological opinions, nor sufficient basis for supporting the contrary assertions" (IB10072). ESA critics cite this report as evidence that the standard of protection for endangered species is too high, that important human needs are ignored, and that decisions about species protection are not made on the basis of sound science. Environmentalists, however, defend the act, believing "that we should apply the precautionary principle to save all the pieces since we lack the knowledge to pick and choose among species." (RS21264)

The Upper Klamath basin is a key example in recent arguments that the ESA does not employ sound science. This question is a tricky one; as The Endangered Species Act and Sound Science puts it, "ESA decisions should be based on sound science, but that phrase can mean different things to different people." Many environmental scientists argue that population viability analysis and modeling have become crucial tools in deciding whether a species is endangered or threatened. These techniques, however, do not employ field testing or peer review, which are part of many traditional definitions of good science. More contemporary definitions might claim that sound science evolves, and is defined by, a community of scientific practitioners. In 2003, House Bill 4840 was sent out of committee; it mandates that ESA decisions use sound science, including field testing and peer review. As of this writing the bill has not had a floor vote. The controversies over ESA enforcement remain frozen in an ideological and political limbo.