The doctrine of pendent jurisdiction allows an admiralty court to entertain a claim not cognizable in admiralty, in addition to the admiralty claim.  Such claims may not be incident to an admiralty claim. 

Pendent jurisdiction exists whenever there is a claim arising under the federal Constitution, the laws of the United States, and treaties made, or which shall be made, under their authority, U.S. Const. art. III, § 2, and the relationship between that claim and a state claim permits the conclusion that the entire action before the court comprises but one constitutional “case.” The federal claim must have substance sufficient to confer subject matter jurisdiction on the court. The state and federal claims must derive from a common nucleus of operative fact.  Generally, a plaintiff prefers to try all his or her claims in one judicial proceeding. Pendent jurisdiction provides judicial economy, convenience and fairness to litigants.  By utilizing pendent jurisdiction in an admiralty case, a claim for damages arising out of a collision on navigable waters occurring during the course of maritime commerce can be adudicated in admiralty courts, although the plaintiff has chosen to employ non maritime theories.[i]

However, pendent jurisdiction need not be exercised in every case where it is found to exist. In Indep. Bankers Ass’n of N.Y. State, Inc. v. Marine Midland Bank, N.A., 575 F. Supp. 1425 (W.D.N.Y. 1983), the court held that it has consistently been recognized that pendent jurisdiction is a doctrine of discretion, not of plaintiff’s right. If pendent jurisdiction does not provide judicial economy, convenience and fairness to litigants, a federal court should not exercise jurisdiction over state claims, even though bound to apply state law to them.

[i] Ohio Barge Line, Inc. v. Dravo Corp., 326 F. Supp. 863 (W.D. Pa. 1971)