There are five known marine sea turtles in Vietnam: green sea, loggerhead, olive ridley, hawksbill, and leatherback.

The union said at a national workshop in Da Nang on Saturday that the last two were not found off Vietnam's northern and central coasts in its 2017 survey, said a report from the Ministry of Natural Resources and Environment.

The species has seen a steep decline elsewhere in Vietnam too, with the number of animals laying eggs annually in Vietnam decreasing more from around 10,000 in the 1980s to 450 this year, a study by the union and the Institute of Marine Environmental Research found.

IUCN data shows that olive ridleys mostly lay their eggs in Con Dao island off the southern coast.

Most sea turtles are classified as endangered and needing prioritized protection. Hunting or trading of any of the five, which are also listed in Vietnam's Red Book of endangered species, is a crime in the country.

The urgent need to conserve and protect the turtles was the central theme of the workshop, organized by the IUCN and Directorate of Fisheries.

Their existence is threatened by habitat destruction, illegal fishing and illegal trade in the creatures.

Plastic waste is also having a serious impact on marine creatures, including on turtles, which are at huge risk of fatally ingesting plastic debris at all stages of their life cycle.

By 2050 there will be around 12 billion tons of plastic litter in landfills and the environment if current consumption patterns and waste management practices continue, according to a United Nations Environment Program report in 2018.

Most plastics do not biodegrade, and instead slowly break down into smaller fragments known as microplastics, which can take thousands of years to decompose.

An estimated 99 percent of seabirds would have ingested plastic by 2050 while 15 percent of all marine species will be affected by ingestion of and entanglement with marine litter.

Many Vietnamese localities have established protected areas and breeding grounds for marine turtles and sought to heighten awareness of their conservation.

The government has approved a Ministry of Agriculture and Rural Development action plan for 2016 – 25 to conserve marine fauna populations and habitats.

It was also revealed at the workshop that Con Dao National Park has been accepted as a member of the Indian Ocean – Southeast Asia Region Marine Turtle Site Network.

In August three turtle species endemic to Vietnam were included in an international list of species facing extinction: the southern Vietnamese box turtle, the Vietnamese pond turtle and the Bourret's box turtle.

Their existence is mainly threatened by trade as exotic pets or for food and habitat loss.

Last month the government approved the construction of three conservation areas and two turtle rescue centers for endangered species in the central region to protect the Vietnamese pond turtle, the Yangtze giant softshell turtle and Asian box turtle.

Last year, the world's rarest turtle found in Hanoi was said to receive breeding and habitat protection plans by the city government. The Rafetus swinhoei, or Hoan Kiem (Sword Lake) turtle is an all but extinct soft-shell species. At least one each is known to live in Xuan Khanh and Dong Mo lakes in the capital's Son Tay Town.

The amphibian is revered in Vietnam. In 2016, the Hoan Kiem turtle estimated to have lived for 200 years died.