The island was described in 1821 by Fildes, who also recorded that some spars and an anchor stock of the Spanish ship San Telmo (commanded by Joaquin Toledo) were found by sealers on Half Moon Beach at about that time The San Telmo was the flagship of a Spanish naval squadron which sailed from Cadiz on 10 May 1819 in company with the Alexandro,the Primeroso-Mariana and the Prueba on a voyage to Lima to assist the suppression of the independence movement in South America. She became dismasted and without steerage in a storm in Drake Passage and was taken in tow by the Primeroso-Mariana at about 61°S 60°W but, the tow failing, the San Telmo was finally left to her fate around 62°S on 4 September 1819.
Following air photography by the Falkland Islands and Dependencies Aerial Survey Expedition in 1956-57, the island was named after the Spanish ship.
Antarctic Specially Protected Area
The island, along with nearby Cape Shirreff, has been designated an 'Antarctic Specially Protected Area' (ASPA No. 149) for the diversity of its plant and animal life, especially its penguin and fur seal breeding colonies.
- "Cape Shirreff and San Telmo Island, Livingston Island, South Shetland Islands". Management Plan for Antarctic Specially Protected Area No. 149: Measure 2, Annex H. Antarctic Treaty Secretariat. 2005. http://www.ats.aq/documents/recatt/Att275_e.pdf.