Question: What is the only trade union on the island country where the islet of Avalau is located?

full_context: Document 1: 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 2: Tuvalu: Tuvalu participates in the work of Secretariat of the Pacific Community, or SPC (sometimes Pacific Community) and is a member of the Pacific Islands Forum, the Commonwealth of Nations and the United Nations. Tuvalu has maintained a mission at the United Nations in New York City since 2000. Tuvalu is a member of the World Bank and the Asian Development Bank. On 18 February 2016 Tuvalu signed the Pacific Islands Development Forum Charter and formally joined the Pacific Islands Development Forum (PIDF).
Document 3: 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 4: 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 5: Tuvalu: Funafuti is the largest atoll of the nine low reef islands and atolls that form the Tuvalu volcanic island chain. It comprises numerous islets around a central lagoon that is approximately 25.1 kilometres (15.6 miles) (N–S) by 18.4 kilometres (11.4 miles) (W-E), centred on 179°7'E and 8°30'S. On the atolls, an annular reef rim surrounds the lagoon with several natural reef channels. Surveys were carried out in May 2010 of the reef habitats of Nanumea, Nukulaelae and Funafuti and a total of 317 fish species were recorded during this Tuvalu Marine Life study. The surveys identified 66 species that had not previously been recorded in Tuvalu, which brings the total number of identified species to 607.
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: 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.
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: 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 10: Funamanu: Funamanu is a small narrow island that is part of Funafuti atoll in Tuvalu. It is a motu (islet) or very small island and is located 2.6 miles southwestward of the southwest tip of Funafuti. The islet is known to be covered in coconut trees which grow 70 feet high. Te Ava Pua Pua is the passage through the reef, with a least depth of 12.7 metres, between the islets of Funamanu to the north and Fale Fatu to the south, in the southeast of Funafuti atoll.
Document 11: Funafuti: Funafuti is an atoll and the capital of the island nation of Tuvalu. It has a population of 6,025 people, making it the country's most populated atoll, with 56.6 percent of Tuvalu's population. It is a narrow sweep of land between 20 and 400 metres (66 and 1,312 feet) wide, encircling a large lagoon (Te Namo) 18 km (11 miles) long and 14 km (9 miles) wide. The average depth in the Funafuti lagoon is about 20 fathoms (36.5 metres or 120 feet). With a surface of 275 square kilometres (106.2 sq mi), it is by far the largest lagoon in Tuvalu. The land area of the 33 islets aggregates to 2.4 square kilometres (0.9 sq mi), less than one percent of the total area of the atoll. Cargo ships can enter Funafuti's lagoon and dock at the port facilities on Fongafale.
Document 12: Avalau: Avalau is an islet within the atoll of Funafuti, Tuvalu. Charles Hedley described Avalau in 1896 "this islet is said to possess a spring of fresh water".
Document 13: 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 14: 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 15: Funafala: Funafala is an islet of Funafuti, Tuvalu that is inhabited by five families, with a church also located on the islet. Funafala means 'the pandanus of Funa', the name of a chief, after whom also the group has been named Funafuti.
ground_truth: Tuvalu Overseas Seamen's Union
sub_queries: Avalau >> country Answer: Tuvalu
What is the only trade union on Tuvalu ? Answer: Tuvalu Overseas Seamen's Union