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With respect to the imposition of the 2,200 yard shutdown zone, the District Court noted evidence of the harm that MFA sonar poses to marine mammals, and then concluded that “[t]he Court therefore is persuaded that while the 2200 yard shutdown requirement may protect marine mammals from the harshest of sonar-related consequences, it represents a minimal imposition [on] the Navy’s training exercises.” Id., at 1119. The District Court did not there explain the basis for that conclusion. With respect to the imposition of the surface ducting condition, the District Court said nothing about the Navy’s interests at all. Id., at 1120–1121.
While a District Court is often free simply to state its conclusion in summary fashion, in this instance neither that conclusion, nor anything else I have found in the District Court’s opinion, answers the Navy’s documented claims that the two extra conditions the District Court imposed will, in effect, seriously interfere with its ability to carry out necessary training exercises.
The first condition requires the Navy to reduce the power of its sonar equipment by 75% when the ship en-counters a condition called “surface ducting” that occurs when the presence of layers of water of different temperature make it unusually difficult for sonar operators to determine whether a diesel submarine is hiding below. Rear Admiral John Bird, an expert in submarine warfare, made clear that the 75% power-reduction requirement was equivalent to forbidding any related training. App. to Pet. for Cert. 297a. But he says in paragraph 52 of his declaration: “Training in surface ducting conditions is critical to effective training because sonar operators need to learn how sonar transmissions are altered due to surface ducting and how submarines may take advantage of them.” Id., at 299a–300a. The District Court, as far as I can tell, did not even acknowledge in its opinion the Navy’s asserted interest in being able to train under these conditions. 530 F. Supp. 2d, at 1120–1121.

The second condition requires the Navy to expand the sonar “shutdown” area surrounding a ship (i.e., turn off the sonar if a mammal is spotted in the area) from a circle with a radius of about one-tenth of a mile to a circle with a radius of about one mile and a quarter. Both sides agree that this requirement will lead to more shutdowns. Admiral Gary Roughead, Chief of Naval Operations, states in paragraph 12 of his declaration that this expanded zone requirement “will result in increased interruptions to training exercises, . . . vastly increas[ing] the risk of negating training effectiveness, preventing strike group certification, and disrupting carefully orchestrated deployment plans to meet world-wide operational commitments.” App. to Pet. for Cert. 344a. Again, I can find nothing in the District Court’s opinion that specifically explains why this is not so. 530 F. Supp. 2d, at 1119–1120.

Fourth, the Court of Appeals sought, through its own thorough examination of the record, to supply the missing explanations. But those explanations are not sufficient. In respect to the surface ducting conditions, the Court of Appeals rejected the Navy’s contentions on the ground that those conditions are “rar[e],” and the Navy has certified trainings that did not involve any encounter with those conditions. 518 F. 3d, at 701–702. I am not certain, however, why the rarity of the condition supports the District Court’s conclusion. Rarity argues as strongly for training when the condition is encountered as it argues for the contrary.
In respect to the expansion of the “shutdown” area, the Court of Appeals noted that (1) the Navy in earlier exercises had shut down its sonar when marine mammals were sited within about one-half a mile, (2) the Navy has used a larger shutdown area when engaged in exercises with lower frequency sonar equipment, and (3) foreign navies have used larger shutdown areas. Id., at 699–701, and nn. 63, 67. But the Navy’s affidavits state that (1) earlier shutdowns when marine mammals were spotted at farther distances “likely occurred during tactically insignificant times,” App. to Pet. for Cert. 356a, (2) ships with low frequency sonar (unlike the sonar here at issue) have equipment that makes it easier to monitor the larger area, particularly by significantly reducing the number of monitoring personnel necessarily involved, and (3) foreign navy experience is not relevant given the potentially different military demands upon those navies, App. 508–509.

Finally, the Court of Appeals, mirroring a similar District Court suggestion in the language I have quoted, says that “the exercises in southern California are only a subset of the Navy’s training activities involving active sonar.” 518 F. 3d, at 702. It adds that the Navy’s study “shows the Navy is still able to conduct its exercises in alternative locations, in reduced number, or through simulation.” Ibid., n. 69. The Court of Appeals, however, also concluded that the study “provides reasonably de-tailed justifications for why the Southern California Operating Area is uniquely suited to these exercises, and demonstrates that the Navy would suffer a certain hardship if the considered alternatives were employed instead.” Ibid.

Fifth, when the Court of Appeals first heard this case following the District Court’s imposition of a broad, absolute injunction, it held that any injunction must be crafted so that the Navy could continue its training exercises. Noting that the Navy had, in the past, been able to use mitigation measures to “reduce the harmful effects of its active sonar,” it “vacate[d] the stay and remand[ed] this matter to the district court to narrow its injunction so as to provide mitigation conditions under which the Navy may conduct its training exercises.” 508 F. 3d 885, 887 (CA9 2007) (emphasis added). For the reasons just stated, neither the District Court nor the Court of Appeals has explained why we should reject the Navy’s assertions that it cannot effectively conduct its training exercises under the mitigation conditions imposed by the District Court.

I would thus vacate the preliminary injunction imposed by the District Court to the extent it has been challenged by the Navy. Neither the District Court nor the Court of Appeals has adequately explained its conclusion that the balance of the equities tips in favor of plaintiffs. Nor do those parts of the record to which the parties have pointed supply the missing explanation.

II

Nonetheless, as the Court of Appeals held when it first considered this case, the Navy’s past use of mitigation conditions makes clear that the Navy can effectively train under some mitigation conditions. In the ordinary course, I would remand so the District Court could, pursuant to the Court of Appeals’ direction, set forth mitigation conditions that will protect the marine wildlife while also enabling the Navy to carry out its exercises. But, at this point, the Navy has informed us that this set of exercises will be complete by January, at the latest, and an EIS will likely be complete at that point, as well. Thus, by the time the District Court would have an opportunity to impose new conditions, the case could very well be moot.
In February of this year, the Court of Appeals stayed the injunction imposed by the District Court—but only pending this Court’s resolution of the case. The Court of Appeals concluded that “[i]n light of the short time before the Navy is to commence its next exercise, the importance of the Navy’s mission to provide for the national defense and the representation by the Chief of Naval Operations that the district court’s preliminary injunction in its cur-rent form will ‘unacceptably risk’ effective training and strike group certification and thereby interfere with his statutory responsibility . . . to ‘organize[e], train[], and equip[] the Navy,’” interim relief was appropriate, and the court then modified the two mitigation conditions at issue. 518 F. 3d 704, 705 (CA9 2008).

With respect to the 2,200 yard shutdown zone, it required the Navy to suspend its use of the sonar if a marine mammal is detected within 2,200 yards, except when sonar is being used at a “critical point in the exercise,” in which case the amount by which the Navy must power down is proportional to the mammal’s proximity to the sonar. Id., at 705–706 (internal quotation marks omitted). With respect to surface ducting, the Navy is only required to shut down sonar altogether when a marine mammal is detected within 500 meters and the amount by which it is otherwise required to power down is again proportional to the mammal’s proximity to the sonar source. Id., at 705–706. The court believed these conditions would permit the Navy to go forward with its imminently planned exercises while at the same time minimizing the harm to marine wildlife.
In my view, the modified conditions imposed by the Court of Appeals in its February stay order reflect the best equitable conditions that can be created in the short time available before the exercises are complete and the EIS is ready. The Navy has been training under these conditions since February, so allowing them to remain in place will, in effect, maintain what has become the status quo. There fore, I would modify the Court of Appeals’ February29, 2008, order so that the provisional conditions it contains remain in place until the Navy’s completion of an acceptable EIS.

GINSBURG, J., dissenting

SUPREME COURT OF THE UNITED STATES
No. 07–1239

DONALD C. WINTER, SECRETARY OF THE NAVY,
ET AL., PETITIONERS v. NATURAL RESOURCES
DEFENSE COUNCIL, INC., ET AL.
ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF
APPEALS FOR THE NINTH CIRCUIT
[November 12, 2008]

JUSTICE GINSBURG, with whom JUSTICE SOUTER joins, dissenting.

The central question in this action under the National Environmental Policy Act of 1969 (NEPA) was whether the Navy must prepare an environmental impact statement (EIS). The Navy does not challenge its obligation to do so, and it represents that the EIS will be complete in January 2009—one month after the instant exercises conclude. If the Navy had completed the EIS before taking action, as NEPA instructs, the parties and the public could have benefited from the environmental analysis—and the Navy’s training could have proceeded without interruption. Instead, the Navy acted first, and thus thwarted the very purpose an EIS is intended to serve. To justify its course, the Navy sought dispensation not from Congress, but from an executive council that lacks authority to countermand or revise NEPA’s requirements. I would hold that, in imposing manageable measures to mitigate harm until completion of the EIS, the District Court conscientiously balanced the equities and did not abuse its discretion.

I

In December 2006, the Navy announced its intent to prepare an EIS to address the potential environmental effects of its naval readiness activities in the Southern California (SOCAL) Range Complex. See 71 Fed. Reg. 76639 (2006). These readiness activities include expansion and intensification of naval training, as well as re-search, development, and testing of various systems and weapons. Id., at 76639, 76640. The EIS process is under-way, and the Navy represents that it will be complete in January 2009. Brief for Petitioners 11; Tr. of Oral Arg. 11.

In February 2007, seeking to commence training before completion of the EIS, the Navy prepared an Environ-mental Assessment (EA) for the 14 exercises it planned to undertake in the interim. See App. L to Pet. for Cert. 235a.1 On February 12, the Navy concluded the EA with a finding of no significant impact. App. 225–226. The same day, the Navy commenced its training exercises. Id., at 227 (“The Proposed Action is hereby implemented.”).
On March 22, 2007, the Natural Resources Defense Council (NRDC) filed suit in the U. S. District Court for the Central District of California, seeking declaratory and injunctive relief based on the Navy’s alleged violations of NEPA and other environmental statutes. As relevant here, the District Court determined that NRDC was likely to succeed on its NEPA claim and that equitable principles warranted preliminary relief. On August 7, 2007, the court enjoined the Navy’s use of mid-frequency active(MFA) sonar during the 11 remaining exercises at issue.
On August 31, the Court of Appeals for the Ninth Circuit stayed the injunction pending disposition of the Navy’s appeal, and the Navy proceeded with two more exercises. In a November 13 order, the Court of Appeals vacated the stay, stating that NRDC had shown “a strong likelihood of success on the merits” and that preliminary injunctive relief was appropriate. 508 F. 3d 885, 886 (2007). The Court of Appeals remanded, however, instructing the District Court to provide mitigation measures under which the Navy could conduct its remaining exercises.
On remand, the District Court received briefing from both parties. In addition, the court “toured the USS Mil-ius at the naval base in San Diego, California, to improve its understanding of the Navy’s sonar training procedures and the feasibility of the parties’ proposed mitigation measures. Counsel for both [parties] were present.” 530
F. Supp. 2d 1110, 1112 (2008). On January 3, 2008, the District Court entered a modified preliminary injunction imposing six mitigation measures. The court revised the modified injunction slightly on January 10 in response to filings by the Navy, and four days later, denied the Navy’s application for a stay pending appeal. On the following day, January 15, the Council on Environmental Quality (CEQ), an advisory body within the Executive Office of the President, responded to the Navy’s request for “alternative arrangements” for NEPA compliance. App. L to Pet. for Cert. 233a. The “arrangements” CEQ set out purported to permit the Navy to continue its training without timely environmental review. Id., at 241a–247a. The Navy accepted the arrangements on the same day. App. 228.
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