Question: Who discovered the country which contains the islet of Sakalua?

full_context: Document 1: Tuvalu: In 1568, Spanish navigator Álvaro de Mendaña was the first European to sail through the archipelago, sighting the island of Nui during his expedition in search of Terra Australis. In 1819 the island of Funafuti was named Ellice's Island; the name Ellice was applied to all nine islands after the work of English hydrographer Alexander George Findlay. The islands came under Britain's sphere of influence in the late 19th century, when each of the Ellice Islands was declared a British Protectorate by Captain Gibson of HMS Curacoa between 9 and 16 October 1892. The Ellice Islands were administered as British protectorate by a Resident Commissioner from 1892 to 1916 as part of the British Western Pacific Territories (BWPT), and then as part of the Gilbert and Ellice Islands colony from 1916 to 1974.
Document 2: Saint Helena: There are several rocks and islets off the coast, including: Castle Rock, Speery Island, the Needle, Lower Black Rock, Upper Black Rock (South), Bird Island (Southwest), Black Rock, Thompson's Valley Island, Peaked Island, Egg Island, Lady's Chair, Lighter Rock (West), Long Ledge (Northwest), Shore Island, George Island, Rough Rock Island, Flat Rock (East), the Buoys, Sandy Bay Island, the Chimney, White Bird Island and Frightus Rock (Southeast), all of which are within one kilometre (0.62 miles) of the shore.
Document 3: Tuvalu: In 1892 Captain Davis of the HMS Royalist reported on trading activities and traders on each of the islands visited. Captain Davis identified the following traders in the Ellice Group: Edmund Duffy (Nanumea); Jack Buckland (Niutao); Harry Nitz (Vaitupu); John (also known as Jack) O'Brien (Funafuti); Alfred Restieaux and Emile Fenisot (Nukufetau); and Martin Kleis (Nui). During this time, the greatest number of palagi traders lived on the atolls, acting as agents for the trading companies. Some islands would have competing traders while dryer islands might only have a single trader.
Document 4: Motulalo: Motulalo is the largest islet of Nukufetau, Tuvalu. The traditional history of Nukufetau recalls that in order to protect the atoll from raiders from Tonga, Tauasa, an aliki (chief), was given Motulalo. Tauasa would pull up coconut trees and throw them at the raiders.
Document 5: Fale, Tuvalu: Fale is an islet of Nukufetau, Tuvalu. The traditional history of Nukufetau recalls that in order to protect the atoll from raiders from Tonga, Lagitupu and Laupapa, two aliki (chiefs) protected Fale. Lagitupu and Laupapa created a trap at a place still called Tututekolo, which was beside a path which led to the beach, where they would surprise the raiders and spear them or split their skulls with an axe made from shells.
Document 6: Marshall Islands: Spanish explorer Alonso de Salazar was the first European to see the islands in 1526, commanding the ship Santa Maria de la Victoria, the only surviving vessel of the Loaísa Expedition. On August 21, he sighted an island (probably Taongi) at 14°N that he named "San Bartolome".
Document 7: Savave: Savave or Saveve is an islet of Nukufetau, Tuvalu, which is on the lagoon side of Fale islet. It is also the name of the small village on the island. In the late 19th century, after the coming of the missionaries, the people of Nukufetau lived on Fale islet before shifting to Savave which is on the lagoon side of the Fale settlement.
Document 8: Lafanga: Lafanga or Lafaga is an islet of Nukufetau, Tuvalu. The traditional history of Nukufetau recalls that in order to protect the atoll from raiders from Tonga, Fialua, an Aliki (chief), was given Lafanga, which is the largest of the eastern islets of Nukufetau. Fialua would attack raiders with his club and bury the bodies at a place called Temata.
Document 9: Sakalua: Sakalua is an islet of Nukufetau, Tuvalu. In the 19th century whalers established a shore camp on Sakalua where coal was used to melt down the whale blubber. The islet has been known as 'Coal Island'.
Document 10: Marshall Islands: Micronesian colonists gradually settled the Marshall Islands during the 2nd millennium BC, with inter-island navigation made possible using traditional stick charts. Islands in the archipelago were first explored by Europeans in the 1520s, with Spanish explorer Alonso de Salazar sighting an atoll in August 1526. Other expeditions by Spanish and English ships followed. The islands derive their name from British explorer John Marshall, who visited in 1788. The islands were historically known by the inhabitants as "jolet jen Anij" (Gifts from God).
Document 11: Motumua: Motumua is an islet of Nukufetau, Tuvalu to the east of Fale islet. On 11 February 1947 the community of Nukufetau opened a boarding school on Motumua so that the children of the island could get an education. The school continued until 1951 when the Education Department requested that it be transferred to Savave and become the government primary school for Nukufetau.
Document 12: Fualopa: Fualopa is an islet of Funafuti, Tuvalu. It is part of the Funafuti Conservation Area, established in 1996 with the aim of preserving the natural fauna and flora of the area. Fualopa hosts a breeding colony of black noddy ("Anous minutus" or white-capped noddy).
Document 13: Guam: The indigenous Chamorros settled the island approximately 4,000 years ago. Portuguese explorer Ferdinand Magellan, while in the service of Spain, was the first European to visit the island, on March 6, 1521. Guam was colonized by Spain in 1668 with settlers, including Diego Luis de San Vitores, a Catholic Jesuit missionary. Between the 16th century and the 18th century, Guam was an important stopover for the Spanish Manila Galleons. During the Spanish -- American War, the United States captured Guam on June 21, 1898. Under the Treaty of Paris, Spain ceded Guam to the United States on December 10, 1898. Guam is among the seventeen non-self - governing territories listed by the United Nations.
Document 14: Tuvalu: Captain John Byron passed through the islands of Tuvalu in 1764 during his circumnavigation of the globe as captain of the Dolphin (1751). Byron charted the atolls as Lagoon Islands. Keith S. Chambers and Doug Munro (1980) identified Niutao as the island that Francisco Mourelle de la Rúa sailed past on 5 May 1781, thus solving what Europeans had called The Mystery of Gran Cocal. Mourelle's map and journal named the island El Gran Cocal ('The Great Coconut Plantation'); however, the latitude and longitude was uncertain. Longitude could only be reckoned crudely as accurate chronometers were unavailable until the late 18th century.
Document 15: Tuvalu: The next European to visit was Arent Schuyler de Peyster, of New York, captain of the armed brigantine or privateer Rebecca, sailing under British colours, which passed through the southern Tuvaluan waters in May 1819; de Peyster sighted Nukufetau and Funafuti, which he named Ellice's Island after an English Politician, Edward Ellice, the Member of Parliament for Coventry and the owner of the Rebecca's cargo. The name Ellice was applied to all nine islands after the work of English hydrographer Alexander George Findlay.
ground_truth: Álvaro de Mendaña
sub_queries: Sakalua >> country Answer: Tuvalu
Who was the discoverer of Tuvalu ? Answer: Álvaro de Mendaña