Question: What is the only trade union on the country Sakalua is located?

full_context: Document 1: Tuvalu: Fetuvalu offers the Cambridge syllabus. Motufoua offers the Fiji Junior Certificate (FJC) at year 10, Tuvaluan Certificate at Year 11 and the Pacific Senior Secondary Certificate (PSSC) at Year 12, set by the Fiji-based exam board SPBEA. Sixth form students who pass their PSSC go on to the Augmented Foundation Programme, funded by the government of Tuvalu. This program is required for tertiary education programmes outside of Tuvalu and is available at the University of the South Pacific (USP) Extension Centre in Funafuti.
Document 2: 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 3: 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 4: Tuvalu: Required attendance at school is 10 years for males and 11 years for females (2001). The adult literacy rate is 99.0% (2002). In 2010, there were 1,918 students who were taught by 109 teachers (98 certified and 11 uncertified). The teacher-pupil ratio for primary schools in Tuvalu is around 1:18 for all schools with the exception of Nauti School, which has a teacher-student ratio of 1:27. Nauti School on Funafuti is the largest primary in Tuvalu with more than 900 students (45 percent of the total primary school enrolment). The pupil-teacher ratio for Tuvalu is low compared to the Pacific region (ratio of 1:29).
Document 5: 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 6: Tuvalu: Tuvaluans are well known for their seafaring skills, with the Tuvalu Maritime Training Institute on Amatuku motu (island), Funafuti, providing training to approximately 120 marine cadets each year so that they have the skills necessary for employment as seafarers on merchant shipping. The Tuvalu Overseas Seamen's Union (TOSU) is the only registered trade union in Tuvalu. It represents workers on foreign ships. The Asian Development Bank (ADB) estimates that 800 Tuvaluan men are trained, certified and active as seafarers. The ADB estimates that, at any one time, about 15% of the adult male population works abroad as seafarers. Job opportunities also exist as observers on tuna boats where the role is to monitor compliance with the boat's tuna fishing licence.
Document 7: 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 8: 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 9: Tuvalu: Funafuti is the only port but there is a deep-water berth in the harbour at Nukufetau. The merchant marine fleet consists of two passenger/cargo ships Nivaga III and Manu Folau. These ships carry cargo and passengers between the main atolls and travel between Suva, Fiji and Funafuti 3 to 4 times a year. The Nivaga III and Manu Folau provide round trip visits to the outer islands every three or four weeks. The Manu Folau is a 50-metre vessel that was a gift from Japan to the people of Tuvalu. In 2015 the United Nations Development Program (UNDP) assisted the government of Tuvalu to acquire MV Talamoana, a 30-metre vessel that will be used to implement Tuvalu's National Adaptation Programme of Action (NAPA) to transport government officials and project personnel to the outer islands. In 2015 the Nivaga III was donated by the government of Japan; it replaced the Nivaga II, which had serviced Tuvalu from 1989.
Document 10: 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 11: 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 12: Tuvalu: New Zealand has an annual quota of 75 Tuvaluans granted work permits under the Pacific Access Category, as announced in 2001. The applicants register for the Pacific Access Category (PAC) ballots; the primary criteria is that the principal applicant must have a job offer from a New Zealand employer. Tuvaluans also have access to seasonal employment in the horticulture and viticulture industries in New Zealand under the Recognised Seasonal Employer (RSE) Work Policy introduced in 2007 allowing for employment of up to 5,000 workers from Tuvalu and other Pacific islands. Tuvaluans can participate in the Australian Pacific Seasonal Worker Program, which allows Pacific Islanders to obtain seasonal employment in the Australian agriculture industry, in particular cotton and cane operations; fishing industry, in particular aquaculture; and with accommodation providers in the tourism industry.
Document 13: 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 14: Tuvalu: Community Training Centres (CTCs) have been established within the primary schools on each atoll. The CTCs provide vocational training to students who do not progress beyond Class 8 because they failed the entry qualifications for secondary education. The CTCs offer training in basic carpentry, gardening and farming, sewing and cooking. At the end of their studies the graduates can apply to continue studies either at Motufoua Secondary School or the Tuvalu Maritime Training Institute (TMTI). Adults can also attend courses at the CTCs.
Document 15: Amatuku: Amatuku is an islet of Funafuti, Tuvalu on which the Tuvalu Maritime Training Institute is located. Access to Amatuku is from Tengako, which is the peninsula at the north end of Fongafale islet.
ground_truth: Tuvalu Overseas Seamen's Union
sub_queries: Sakalua >> country Answer: Tuvalu
What is the only trade union on Tuvalu ? Answer: Tuvalu Overseas Seamen's Union