Just Sayin' . . .

All hail Fabious Maximus:

1. The US Constitution. Article I, section 8: Congress shall have power … To define and punish Piracies and Felonies committed on the high Seas, and Offenses against the Law of Nations.

2. Under U.S. Law, there is already authority for Civilian Mariners to defend against pirates and seize pirated vessels. 33 U.S.C. 383: Resistance of pirates by merchant vessels (source)The commander and crew of any merchant vessel of the United States, owned wholly, or in part, by a citizen thereof, may oppose and defend against any aggression, search, restraint, depredation, or seizure, which shall be attempted upon such vessel, or upon any other vessel so owned, by the commander or crew of any armed vessel whatsoever, not being a public armed vessel of some nation in amity with the United States, and may subdue and capture the same; and may also retake any vessel so owned which may have been captured by the commander or crew of any such armed vessel, and send the same into any port of the United States.