Order Code RS21264
July 16, 2002
CRS Report for Congress
Received through the CRS Web
The Endangered Species Act
and “Sound Science”
Pamela Baldwin
Legislative Attorney
American Law Division
M. Lynne Corn
Specialist in Natural Resources Policy
Resources, Science, and Industry Division
Summary
The Endangered Species Act is a strong statute enacted to save and recover
dwindling species. Decisions to list species are to rest only on the best available
scientific data, and science plays a part in other important aspects of the Act. Yet many
times the best available science may be sketchy. Recent situations involving economic
and social conflicts over resources have resulted in a renewed focus on the use of
science under the ESA and several proposals are before Congress. This report provides
background on the issues and will be updated as circumstances warrant.
The Endangered Species Act (ESA)1 was enacted to conserve listed species – to
bring them to the point where they do not need the special protections of the Act2 – and
to protect the ecosystems of which dwindling species are a part.3 Dwindling species often
reflect endangered resources or ecosystems. Recent situations4 in which there have been
economic and social disruptions as a result of listings under the ESA have resulted in a
renewed focus on the protective posture of the Act5 and on the use of science under it. All
agree that ESA decisions should be based on “sound science,” but that phrase can mean
different things to different people.
1 Pub. L. No. 93-205, 87 Stat. 884, 16 U.S.C. §§1531 et seq.
2 Section 3(3), 16 U.S.C. §1532.
3 Section 2(b), 16 U.S.C. §1531(b).
4 See, e.g. CRS Report RL31098, Klamath River Basin Issues: An Overview of Water Use
Conflicts, which discusses the conflicts over water use in that area.
5 See Tennessee Valley Authority v. Hill, 437 U.S. 153 (1978).
Congressional Research Service ˜ The Library of Congress

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The ESA requires that decisions to list a species be made “solely on the basis of the
best scientific and commercial data available ....” There is no elaboration on the meaning
of this phrase in the law itself or in agency regulations. The decision of whether to list
a species or not has been analogized to diagnosing and treating cancer: whether a patient
has cancer should be a strictly scientific decision; other factors can be considered in
deciding how to treat the cancer. Similarly, science alone is to be the basis for listing
decisions, but other factors may be considered in post-listing decisions and action.
Moreover, science can also play a role in post-listing decisions and procedures under the
ESA: 1) science informs the designation of critical habitat for listed species; 2) science
is the basis for the evaluations during the consultation process of whether a proposed
agency action may jeopardize the continued existence of a species or result in destruction
of critical habitat, and assists in the development of suggestions for “reasonable and
prudent alternatives” to a proposed agency action so as to avoid jeopardy; 3) it is used to
develop habitat conservation plans and incidental take permits under §10 of the Act; and
4) it is used to develop recovery plans to bring the species to the point where the
protections of the Act are no longer needed.
The word “solely” was added in the 1982 amendments to the ESA6 to clarify that the
determination of endangered or threatened status was intended to be a biological decision
made without reference to economic or other “non-biological” factors. A committee
report discussed why listing was to be solely a scientific decision and also interpreted
“commercial data” as meaning trade data.7 The Conference report in 1982 confirms that
6 Act of October 13, 1982, P.L. 97-304, 96 Stat. 1411.
7 In discussing the addition of the word “solely,” H.R. Rep. No 567, 97th Cong., 2d Sess. (1982)
at 19-20 stated:
... The principal purpose of the amendments to Section 4 is to ensure that decisions
pertaining to the listing and delisting of species are based solely upon biological criteria and to
prevent non-biological considerations from affecting such decisions. To accomplish this and
other purposes, Section 4(a) is amended in several instances.
Section 4(b) of the Act is amended in several instances by Section 1(a)(2) of H.R. 6133.
First, the legislation requires that the Secretary base his determinations regarding the listing or
delisting of species “solely” on the basis of the best scientific and commercial data available to
him. The addition of the word “solely is intended to remove from the process of the listing or
delisting of species any factor not related to the biological status of the species. The Committee
strongly believes that economic considerations have no relevance to determinations regarding the
status of species and intends that the economic analysis requirements of Executive Order 12291,
and such statutes as the Regulatory Flexibility Act and the Paperwork Reduction Act not apply.
The committee notes, and specifically rejects, the characterization of this language by the
Department of the Interior as maintaining the status quo and continuing to allow the Secretary
to apply Executive Order 12291 and other statutes in evaluating alternatives to listing. The only
alternatives involved in the listing of species are whether the species should be listed as
endangered or threatened or not listed at all. Applying economic criteria to the analysis of these
alternatives and to any phase of the species listing process is applying economics to the
determinations made under Section 4 of the Act and is specifically rejected by the inclusion of
the word “solely” in this legislation.
Section 4(b) of the Act, as amended, provides that listings shall be based solely on the basis
of the best “scientific and commercial data” available. The Committee did not change this
information standard because of its interpretation of the word “commercial” to allow the use of
trade data. Retention of the word “commercial” is not intended, in any way, to authorize the use
(continued...)

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it was the intent of both chambers that economic factors not play a role in the designation
and listing of species for protection.8
However, given that the Act addresses species that almost by definition are likely to
be rare, there may be little or no information on many of the species facing extinction, and
insufficient personnel or funds available to conduct studies on many species, especially
those with little charisma or known economic value. What should be done in such
instances? Should decisions be weighted in favor of the species, or perhaps irrigators,
ranchers, or builders? If species are favored, should all species in all cases enjoy
protection, or should only certain species that meet stated criteria be given the benefit of
the doubt? The Act does not expressly address this question, but considering the strongly
protective purpose of the Act – to save and recover species – with the wording of “best
... data available,” arguably the Act intends that all dwindling species should be given the
benefit of the doubt and a margin of safety provided. Many scientists feel this is the
appropriate stance – that we should apply the “precautionary principle” to “save all the
pieces” since we lack the knowledge to pick and choose among species.
This is the position taken in the FWS Handbook at pages 1-6, which states that
efforts should be made to develop information, but if a biological opinion must be
rendered promptly, it should be based on the available information, “giving the benefit
of the doubt to the species,” with consultation possibly being reinitiated if additional
information becomes available. This phrase is drawn from H.R. Conf. Rep. No 697, 96th
Cong., 2d Sess. 12 (1979), which stated the “best information available” language was
intended to allow the FWS to issue biological opinions even when inadequate information
was available, rather than being forced to issue negative opinions, thereby unduly
impeding proposed actions. But the committee report also states that if a biological
opinion is rendered on the basis of inadequate information, the federal agency proposing
7 (...continued)
of economic considerations in the process of listing a species.
8 H.R. Rep. No 835, 97th Cong., 2d Sess. 19 (1982) states:
Section 2 of the Conference substitute amends section 4 of the Act in several ways. The
principal purpose of these amendments is to ensure that decisions in every phase of the process
pertaining to the listing or delisting of species are based solely upon biological criteria and to
prevent non-biological considerations from affecting such decisions.
The Committee of Conference (hereinafter the Committee) adopted the House language
which requires the Secretary to base determinations regarding the listing or delisting of species
“solely” on the basis of the best scientific and commercial data available to him. As noted in the
House Report, economic considerations have no relevance to determinations regarding the status
of species and the economic analysis requirements of Executive Order 12291, and such statutes
as the Regulatory Flexibility Act and the Paperwork Reduction Act, will not apply to any phase
of the listing process. The standards in the Act relating to the designation of critical habitat
remain unchanged. The requirement that the Secretary consider for listing those species that
states or foreign nations have designated or identified as in need of protection also remains
unchanged.
The Committee adopted, with modifications, the Senate amendments which combined and
rewrote section 4(b) and (f) of the Act to streamline the listing process by reducing the time
periods for rulemaking, consolidating public meeting and hearing requirements and establishing
virtually identical procedures for the listing and delisting of species and for the designation of
critical habitat.

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an action has the duty to show its actions will not jeopardize a species and a continuing
obligation to make a reasonable effort to develop additional information, and that the
statutory language “continues to give the benefit of the doubt to the species.”
Recent attention has focused on the use of science in listings, but also in jeopardy
determinations and the development of reasonable and prudent alternatives, and especially
on how to handle situations when the “available” science is not extensive: what new
requirements might be imposed and whether some form of peer review of the science
underlying decisions might be advisable. Some suggest that considerations other than
species conservation should prevail; still others seek a change in the current posture of the
law in this regard by changing the role of “science.” These considerations are
complicated by the fact that acquiring more complete science may be extremely costly and
time-consuming in connection with many lesser-known species; for example, a
requirement for certain data before listing could occur might result in many fewer listings
being completed.
Several bills have required some form of peer review, which may encounter practical
difficulties. For example, there may be few (or no) people in the world knowledgeable
about some species and these specialists often have other duties and may not be available
(or willing) to serve governmental regulators – in some cases constituting peer review
panels could be difficult. Achieving peer review by impartial, unbiased scientists may
also be an issue if the listing or action being reviewed could involve major economic
factors in which the scientists have an interest. The press has been replete with
accusations of “bad” science from all sides.
The Fish and Wildlife Service (FWS) and the National Marine Fisheries Service
(NMFS) developed a joint policy on Information Standards Under the Endangered
Species Act9 that might provide useful information on this issue. Under this policy, FWS
and NMFS receive and use information from a wide variety of sources, including
individuals. 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. Service biologists are to impartially review and evaluate all information for
purposes of listing, consultation, recovery, and permitting actions, and to ensure that any
information used by the Services to implement the Act is “reliable, credible, and
represents the best scientific and commercial data available.” Service biologists are to
document their evaluations of all information and, to the extent consistent with the use
of the best scientific and commercial data available, use primary and original sources of
information as the basis of recommendations. In addition, documents developed by
Service biologists will be reviewed to “verify and assure the quality of the science used
to establish official positions, decisions, and actions ....”
Another joint policy notes that in addition to the public comments received on
proposed listing rules and draft recovery plans, the Services will also formally solicit
expert opinions and peer review to ensure the best biological and commercial information.
With respect to listing decisions, the agencies will solicit the expert opinions of three
specialists and summarize these in the record of final decision. Special independent peer
9 59 Fed. Reg. 34271 (July 1, 1994).

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review can also be used when it is likely to reduce or resolve an unacceptable level of
scientific uncertainty.10
Many of these issues were also studied, described, and discussed in a publication of
the National Research Council, Science and the Endangered Species Act.11 The Council
noted that under the current balance, “the structure of hypothesis testing related to listing
and jeopardy decisions can make it more likely for an endangered species to be denied
needed protection than for an non-endangered species to be protected unnecessarily ....”12
Judicial review can help ensure that agency decisions and their use of scientific data
are not “arbitrary or capricious” and that regulations are rationally related to the problems
causing the decline of a species, especially when other interests are adversely affected.
Courts that have considered the “best data available” language have held that an agency
is not obliged to conduct studies to obtain missing data,13 but cannot ignore available
biological information,14especially if the ignored information is the most current,15 nor
treat one species differently from the way other similarly-situated species are treated.16
The agency may not postpone listing a dwindling species until it is on the brink of
extinction in reliance on possible, but uncertain, future actions of an agency.17 A court
also has said that “the ‘best scientific and commercial data available’ is not a standard of
absolute certainty, and [is] a fact that reflects Congress’ intent that the FWS take
conservation measures before a species is ‘conclusively’ headed for extinction.”18 If the
FWS does not base its listings on speculation or surmise, or disregard superior data, the
fact that the studies it does rely on are imperfect does not undermine those authorities as
the best scientific data available -- “ the Service must utilize the best scientific ... data
available, not the best scientific data possible.”19
On the other hand, one case struck down regulations that totally banned duck hunting
in an area in order to protect one species of duck.20 Another court stated that the bar the
FWS has to clear in terms of evidence is very low, but it must at least clear it and, in the
context of issuance of “Incidental Take Permits” under §10 of the Act, this means the
agency must demonstrate that a species is or could be in an area before regulating it, and
10 59 Fed. Reg. 34270 (July 1, 1994).
11 National Academy Press, Washington, D.C. 1995.
12 Ibid., at 15.
13 Southwest Center for Biological Diversity v. Babbitt, 215 F.3d 58 (D.C. Cir. 2000).
14 Connor v. Burford, 848 F.2d 1441 (9th Cir. 1988).
15 Southwest Center for Biological Diversity v. Babbitt, 926 F. Supp. 920 (D.C. Ariz. 1996).
16 Ibid.
17 Biodiversity Legal Foundation v. Babbitt, 943 F. Supp. 23 (D. D.C. 1996).
18 Defenders of Wildlife v. Babbitt, 958 F. Supp. 670, 680 (D. D.C. 1997).
19 Building Industry Ass’n of Sup. Cal. v. Norton, 247 F.3d 1241, 1246-1267 (D.C. Cir. 2001),
cert. denied 2002 U.S. LEXIS 479.
20 Connor v. Andrus, 453 F. Supp. 1037 (W.D. Tx. 1978).

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must establish the causal connection between the land use being regulated and harm to
the species in question. Mere speculation as to the potential for harm is not sufficient.21
Several bills have been introduced in the 107th Congress seeking to clarify the role
of science in ESA decisions. H.R. 2829/S. 1912 would require that greater weight be
given to scientific or commercial data that is empirical or has been field-tested or peer-
reviewed, while H.R. 3705/H.R. 4840 would modify the listing petition process and
establish independent review boards. H.R. 4840 would also require collection of field
data in all cases before listing could occur.
21 Arizona Cattle Growers Association v. United States Fish and Wildlife Service, 273 F.3d 1229
(9th Cir. 2001).

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