delivered the opinion of the Court.
The Piscataqua River lies at the southeastern end of New Hampshire’s boundary with Maine. The river begins at the headwaters of Salmon Falls and runs seaward into Portsmouth Harbor (also known as' Piscataqua Harbor). On March 6, 2000, New Hampshire brought this original action against Maine, claiming that the Piscataqua River boundary runs along the Maine shore and that the entire river and all of Portsmouth Harbor belong to New Hampshire. Maine has filed a motion to dismiss on the ground that two prior proceedings — a 1740 boundary determination by King George II and a 1977 consent judgment entered by this Court — definitively fixed the Piscataqua River boundary at the middle of the river’s main channel of navigation.
The 1740 decree located the Piscataqua River boundary at the “Middle of the River.” Because New Hampshire, in the 1977 proceeding, agreed without reservation that the words “Middle of the River” mean the middle of the Pis-cataqua River’s main channel of navigation, we conclude that New Hampshire is estopped from asserting now that the boundary runs along the Maine shore. Accordingly, we grant Maine’s motion to dismiss the complaint.
I
New Hampshire and Maine share a border that runs from northwest to southeast. At the southeastern end of the
In the 1970’s contest over the lateral marine boundary, we summarized the history of the interstate boundary in the Piscataqua River region. See
New Hampshire
v.
Maine,
“‘That the Dividing Line shall pass up thro the Mouth of Piscataqua Harbour and up the Middle of the River .... And that the Dividing Line shall part the Isles of Shoals and run thro the Middle of the Har-bour between the Islands to the Sea on the Southerly Side....’ ” Id., at 366 (quoting the 1740 decree).
In 1976, New Hampshire and Maine “expressly agree[d] . . . that the decree of 1740 fixed the boundary in the Pis-cataqua Harbor area.”
Id.,
at 367 (internal quotation marks omitted). “Their quarrel was over the location ... of the ‘Mouth of Piscataqua River,’ ‘Middle of the River,’ and ‘Middle of the Harbour’ within the contemplation of the decree.”
In the course of litigation, New Hampshire and Maine proposed a consent decree in which they agreed,
inter
alia, that the words “Middle of the River” in the 1740 decree refer to the middle of the Piseataqua River’s main channel of navigation. Motion for Entry of Judgment By Consent of Plaintiff and Defendant in
New Hampshire
v.
Maine,
O. T. 1973, No. 64 Orig., p. 2 (hereinafter Motion for Consent Judgment). The Special Master, upon reviewing pertinent history, rejected the States’ interpretation and concluded that “the geographic middle of the river and not its main or navigable channel was intended by the 1740 decree.” Report 41. This Court determined, however, that the States’ interpretation “reasonably invested] imprecise terms” with a definition not “wholly contrary to relevant evidence.”
New Hampshire
v.
Maine,
The 1977 consent judgment fixed only the lateral marine boundary and not the inland Piseataqua River boundary. See Report 42-43 (“For the purposes of the present dispute, ... it is unnecessary to lay out fully the course of the boundary as it proceeds upriver ....”). In the instant action, New Hampshire contends that the inland river boundary “run[s] along the low water mark on the Maine shore,” Complaint 49, and asserts sovereignty over the entire river
While disagreeing with New Hampshire’s understanding of history, see Motion to Dismiss 9-14,18-19 (compiling evidence that Maine continually exercised jurisdiction over the harbor and shipyard from the 1700’s to the present day), Maine primarily contends that the 1740 decree and the 1977 consent judgment divided the Piseataqua River at the middle of the main channel of navigation — a division that places Seavey Island within Maine’s jurisdiction. Those earlier proceedings, according to Maine, bar New Hampshire’s complaint under principles of claim and issue preclusion as well as judicial estoppel.
We pretermit the States’ competing historical claims along with their arguments on the application
vel non
of the res judicata doctrines commonly called claim and issue preclusion. Claim preclusion generally refers to the effect of a prior judgment in foreclosing successive litigation of the very same claim, whether or not relitigation of the claim raises the same issues as the earlier suit. Issue preclusion generally refers to the effect of a prior judgment in foreclosing successive litigation of an issue of fact or law actually
II
“[W]here a party assumes a certain position in a legal proceeding, and succeeds in maintaining that position, he may not thereafter, simply because his interests have changed, assume a contrary position, especially if it be to the prejudice of the party who has acquiesced in the position formerly taken by him.”
Davis
v.
Wakelee,
Although we have not had occasion to discuss the doctrine elaborately, other courts have uniformly recognized that its purpose is “to protect the integrity of the judicial process,”
Edwards
v.
Aetna Life Ins. Co.,
Courts have observed that “[t]he circumstances under which judicial estoppel may appropriately be invoked are probably not reducible to any general formulation of principle,”
Allen,
In enumerating these factors, we do not establish inflexible prerequisites or an exhaustive formula for determining the applicability of judicial estoppel. Additional considerations may inform the doctrine’s application in specific factual contexts. In this case, we simply observe that the factors above firmly tip the balance of equities in favor of barring New Hampshire’s present complaint.
New Hampshire’s claim that the Piseataqua River boundary runs along the Maine shore is clearly inconsistent with its interpretation of the words “Middle of the River” during the 1970’s litigation. As mentioned above, supra, at 747, interpretation of those words was “necessary” to fixing the northern endpoint of the lateral marine boundary, Report 43. New Hampshire offered two interpretations in the earlier proceeding — first agreeing with Maine in the proposed consent decree that “Middle of the River” means the middle of the main channel of navigation, and later agreeing with the Special Master that the words mean the geographic middle of the river. Both constructions located the “Middle of the River” somewhere other than the Maine shore of the Pis-eataqua River.
At oral argument, New Hampshire urged that the consent decree simply fixed the “Middle of the River” at “an arbitrary location based on the administrative convenience of the parties.” Tr. of Oral Arg. 37. To the extent New Hampshire implies that the parties settled the lateral marine boundary dispute without judicial endorsement of their interpretation of “Middle of the River,” that view is foreclosed by the Court’s determination that “[t]he consent decree . . . proposes a wholly permissible final resolution of the controversy both as to facts and law,”
New Hampshire
v.
Maine,
New Hampshire also contends that the 1977 consent decree was entered without “a searching historical inquiry into what that language [‘Middle of the River’] meant.” Tr. of Oral Arg. 39. According to New Hampshire, had it known then what it knows now about the relevant history, it would not have entered into the decree.
Ibid.
We do not question that it may be appropriate to resist application of judicial estoppel “when a party’s prior position was based on inadvertence or mistake.”
John S. Clark Co.
v.
Faggert & Frieden, P. C.,
The pleadings in the lateral marine boundary case show that New Hampshire did engage in “a searching historical inquiry” into the meaning of “Middle of the River.” See Reply Brief for Plaintiff in
New Hampshire
v.
Maine,
O. T. 1975, No. 64 Orig., pp. 3-9 (examining history of river boundaries under international law, proceedings leading up to the 1740 order of the King in Council, and relevant precedents of this Court). None of the historical evidence cited by New Hampshire remotely suggested that the Piscataqua River boundary runs along the Maine shore. In fact, in attempting to place the boundary at the geographic middle of the
Nor can it be said that New Hampshire lacked the opportunity or incentive to locate the river boundary at Maine’s shore. In its present complaint, New Hampshire relies on historical materials — primarily official documents and events from the eolonial and posteolonial periods, see Brief in Opposition to Motion to Dismiss 12-19 — that were no less available 25 years ago than they are today. And New Hampshire had every reason to consult those materials: A river boundary running along Maine’s shore would have placed the northern terminus of the lateral marine boundary much closer to Maine, “resulting] in hundreds if not thousands of additional acres of territory being in New Hampshire rather than Maine,” Tr. of Oral Arg. 48 (rebuttal argument of Maine). Tellingly, New Hampshire at the time understood the importance of placing the northern terminus as close to Maine as possible. While agreeing with the Special Master that “Middle of the River” means geographic middle, New Hampshire insisted that the geographic middle should be determined by using the banks of the river, not low tide elevations (as the Special Master had proposed), as the key reference points — a . methodology that would have placed the northern terminus 350 yards closer to the Maine shore. Plaintiff’s Exceptions 3.
Finally, notwithstanding the balance of equities, New Hampshire points to this Court’s recognition that “ordinarily the doctrine of estoppel or that part of it which precludes inconsistent positions in judicial proceedings is not applied to states,”
Illinois ex rel. Gordon
v.
Campbell,
What has changed between 1976 and today is New Hampshire’s interpretation of the historical evidence concerning the King’s 1740 decree. New Hampshire advances its new interpretation not to enforce its own laws within its borders, but to adjust the border itself. Given Maine’s countervailing interest in the location of the boundary, we are unable to discern any “broad interest] of public policy,” 18 Wright § 4477, p. 784, that gives New Hampshire the prerogative to construe “Middle of the River” differently today than it did 25 years ago.
* * *
For the reasons stated, we conclude that judicial estoppel bars New Hampshire from asserting that the Piscataqua River boundary runs along the Maine shore. Accordingly, we grant Maine’s motion to dismiss the complaint.
It is so ordered.
[Appendix containing Portsmouth Harbor to Isles of Shoals map follows this page.]
[[Image here]]
Adapted from Map 13283, Portsmouth Harbor to Isles of Shoals, National Oceanic and Atmospheric Administration, U.S. Department of Commerce (18th ed. Nov. 2000).
Notes
According to New Hampshire, the Federal Government in recent years has taken steps to dose portions of the shipyard and to lease its land and fadlities to private developers. Complaint 34. New Hampshire and Maine assert competing daims of sovereignty over private development on shipyard lands. Ibid.
