Pedro (erroneously called Antonio in some sources) de Iriarte, explorer and sea captain, commanded one of the two small ships of the second and more important maritime voyage sent by Spain to find the French settlement made on the Texas coast by the La Salle expedition. A youthful but highly regarded "captain of sea and war" in the Armada de Barlovento, Iriarte was second in command of the expedition to Capt. Martín de Rivas. The voyage, piloted by Juan Enríquez Barroto, who made a map and kept a diary, and Antonio Romero, left Veracruz on December 25, 1686, to return on July 3 and 4, 1687, after a complete circumnavigation of the Gulf. As the younger of the two captains, Iriarte often took charge of the explorations made from the two ships in small boats. His men discovered the wreck of La Salle's ship Belle, stranded on Matagorda Peninsula. He was close at hand when some of his men seized a Karankawa Indian in an effort to persuade him to go aboard the vessels and provoked a brief skirmish before the Indians took flight.
At the conclusion of the voyage, Iriarte and the two pilots went to Mexico City to report to the Viceroy Monclova (Captain Rivas being too ill to make the journey). The same three officers were summoned to the capital again, upon the return of captains Francisco López de Gamarra and Andrés de Pez, to examine and comment on the diary of their voyage. The time and place of Iriarte's birth and death are not known. He evidently outlived most of those who commanded ships in the La Salle search except Pez.