Ransom-hungry pirates, polar explorers, offshore oil giants - the race for the riches of the world's final frontier is on.
From Thailand to Alaska, the battle to tap ever-dwindling resources from minerals to fish is spurring new conflicts over who has the right to the treasures of the deep seas.
As India, China and Brazil seek new sources of cobalt, copper and nickel to build the gadgets demanded by their booming populations, they are preparing to mine a new realm - the dark depths of the ocean.
Over the next decade India will spend more than $1 billion to develop and test deep sea technologies - including human-piloted exploration submarines - in the Indian Ocean that could give access to once inaccessible mineral riches up to 6.8 miles (11 km) under water.
"We have to depend on ocean resources sooner or later ... there is no other way," said Gidugu Ananda Ramadass, head of India's deep sea mining project at the National Institute of Ocean Technology in the southern city of Chennai.
But mining the seas - home to the vast majority of life on Earth - carries huge risks and could cause irreversible damage to the environment, campaigners warn.
Oceans - which scientists say are less understood than the moon or Mars - cover more than 70 percent of the earth's surface, yet less than 20 percent of their seafloor has been mapped or observed, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).
And what lies below the waves is worth trillions of dollars.
The so-called "blue economy" of marine resources is expected to contribute $3 trillion to the world's GDP by 2030 - equivalent to the size of the UK economy - up from $1.5 trillion in 2010, according to the Organisation for Economic Co-operation and Development (OECD).
But from overfishing, to a rush to mine deep seas, to slavery on fishing boats, the world's oceans are a source of growing dispute, not least over who should get access to them.
Experts say oceans are a neglected area of global governance despite the United Nations' 1982 Convention on the Law of the Sea (UNCLOS) and the 193 member states agreeing in 2015 to a global goal to sustainably manage and protect marine resources.
"Oceans governance is the classic public good challenge," said Dominic Waughray, head of the World Economic Forum's Centre for Global Public Goods.
Smart rules are essential to keep oceans healthy - but because nobody owns them, "we have a real problem", he said.
Liz Karan, senior manager for the high seas at Pew Charitable Trusts, a non-profit organisation, said existing regulations are patchy and have struggled to protect ecosystems in international waters.
But a proposed U.N. treaty to protect ocean biodiversity - and prevent over-exploitation - could change that.
Negotiations on a legally binding treaty – which would cover the high seas, or ocean areas that extend beyond national boundaries capped at 200 nautical miles from coasts – began in September and aim to reach an agreement by 2020.
But government and U.N. action are only part of the answer, experts caution.
"Governments are good at setting targets, but to really get things done you're going to need more than hoping U.N. agencies alone can fix this," said Waughray.
He said technology and monitoring tools to enforce the would-be treaty would be crucial.
So who are the main players controlling Earth's final frontier? And how will the global hunt for resources impact the communities who now depend on the seas to survive?
From fast-expanding tourist resorts to disputes over maritime borders, fishing communities are finding their main source of income increasingly under threat.
In southern Thailand, a tourism boom is pitting the Chao Lay, or people of the sea, against land developers, while marine conservation efforts also limit their traditional fishing grounds.
"Our lives have changed. We have to go further and dive deeper to catch fish, and that is affecting our health," said Ri Fongsaithan, an Urak Lawoi community elder.
According to Brad Adams of Human Rights Watch, an advocacy group, the Chao Lay "generally do not assert ownership rights because they believe that land and water should not be owned or controlled by one person, but rather shared by many".
Phuket, Thailand, in 1971
The legal fight over the sea is also playing out at national levels.
The Latin American nations of Colombia and Nicaragua, for instance, have for decades fought over a cluster of islands in the western Caribbean - and the fishing rights around them.
In 2012, a ruling by the International Court of Justice redrew the maritime borders around the archipelago of San Andres, Providencia, and Santa Catalina in favour of Nicaragua, reducing the expanse of sea belonging to Colombia.
The loss of waters – and of income – has hit the islands' artisanal fishermen hard, with some saying the money they make from fishing cannot even pay for the fuel to power their boats.
Maritime borders between Nicaragua and Colombia after 2012
"Our territory at the end of the day is the ocean," said Erlid Arroyo, secretary of agriculture and fishing at the governor's office in San Andres. He estimated lost income from the court ruling at "millions and millions of dollars".
But the crisis has spurred a rethink of the island's fishing industry, he said, with the government training fishermen to catch fish in other areas and make more of their catch.
These islands' underwater riches may not last, however. In the last few decades, the world's oceans have undergone unprecedented warming while currents have shifted.
From the waters off the east coast of the United States to the coasts of West Africa, the changes are causing fish and other sea life to seek out new waters - leaving the communities that depend on them facing disruption as a result.
For other communities, fishing regulations present the most potent threat.
For decades the Inupiaq, a Native Alaskan group living north of the Arctic Circle, have argued that international limits on subsistence whaling are not big enough to meet their food needs.
"They controlled what we could hunt and what we could eat," said Roy Nageak, a retired whaling captain, referring to when the International Whaling Commission (IWC) set quotas on catching bowhead whales in 1977 to protect existing stocks.
The Inupiaq hired their own scientists to convince the IWC that whale stocks were still healthy and to increase the quota, said Crawford Patkotak, an Inupiaq whaling captain.
Then ensued a constant struggle to negotiate and renew whaling quotas with the IWC - which expired every five-six years - the indigenous group said.
Inupiaq leaders welcomed the International Whaling Commission's decision in September to reaffirm their shared quota of 56 whales per year, increase the number of unused strikes permitted to carry over into the next year, and to renew aboriginal quotas automatically.
"We'll now be able to hunt in peace without the anxiety of worrying about an expiring quota," said Patkotak.
Much of the quest for ocean resources, however, lies not near its surface but in its depths.
Technological advances and growing demand for minerals used in consumer electronics have fueled a rush to mine the deep seas.
When Oscar-winning director James Cameron ventured in 2012 on a record-breaking solo dive to the deepest known place on Earth in the Pacific Ocean, he described a flat, desolate landscape, 50 times larger than the Grand Canyon.
But new technology like autonomous robots and deep-diving submarines could allow scientists to unearth treasures like copper, nickel and cobalt.
Resource-hungry countries are racing ahead in the hunt for minerals, with India planning to explore a 75,000-square-km (29,000 square miles) area of the Indian Ocean - equal to about 2 percent of the country's size.
"We are exploring Mars, we are exploring the moon. Why don't we explore our own oceans?" asked Ramadass, of India's National Institute of Ocean Technology.
China, the world's second-largest economy, is seeking minerals in the eastern Pacific Ocean. And Brazil has won rights to explore the Rio Grande Rise off its southeastern coast, in the southern Atlantic Ocean.
"The more (natural) resources are exhausted on the continent, the more interesting marine mining will become," said Lauro Julio Calliari, an oceanographer at Brazil's Federal University of Rio Grande do Sul.
But, with little of the deep ocean mapped or explored, environmentalists worry about the potential loss of species not yet well understood - or even recorded.
Sediment plumes and disturbance caused by mining could wipe out habitats, including for slow-growing corals and fish, said Richard Mahapatra, managing editor of the New Delhi-based science and environment magazine Down To Earth.
In the longer run, disturbing oceans, which absorb carbon dioxide and heat, could impact how they regulate the world's climate, he added.
"We should not rush (deep sea mining). Otherwise we will head towards another disaster," he said.
The hunt for yet another ocean resource - offshore oil - could have disastrous consequences for marine wildlife, campaigners warn.
Last December, Italian oil producer Eni began drilling a new well in U.S. waters off the north coast of Alaska – the first company to drill in the area since 2015, and a move warily eyed by indigenous communities.
Brower Jr. of the Alaska Eskimo Whaling Commission worries that potentially devastating oil spills could affect whale food sources, including krill.
"Of course we're concerned because we've seen the mess down in the Gulf of Mexico - BP's blowout," he said, referring to the Deepwater Horizon oil drilling rig that exploded in 2010, causing the worst spill in history.
Determining who owns or has the right to the ocean's resources raises another question: Who should police them?
The multi-billion-dollar seafood industry has come under scrutiny – particularly in Thailand – after investigations showed widespread slavery, human trafficking and violence on fishing boats and in onshore processing facilities.
Experts said slavery was also rife on fishing vessels in Cape Town's luxurious waterfront.
Part of the problem stems from a lack of oversight on fishermen's working conditions on the high seas, said Brandt Wagner, head of the transport and maritime unit at the International Labour Organization, a U.N. agency.
The main international convention regulating crew safety and conditions on fishing vessels - called the Cape Town Agreement - was adopted in 2012 by the International Maritime Organization (IMO), a U.N. agency.
But only 10 countries have signed it, according to the Pew Charitable Trusts, a non-profit.
"So the international law which is most needed to make sure the fishing vessels are safe is not yet in force," said Wagner.
Dane du Plessis, with South African charity Biblia, has tried to identify and help exploited fishermen when their boats dock in the port of Cape Town.
"People ignore what's going on because these fishermen, they're poor, they're uneducated," he said,
Migrant fishermen told the Thomson Reuters Foundation they were routinely abused by employers, including being punched, forced to drink dirty water and subjected to racist slurs.
In May a Taiwanese trawler was detained – and later released – in Cape Town after crew complaints about working conditions.
The detention was the first under the International Labour Organization's Fishing Convention , which seeks to improve fishermen's working conditions.
Du Plessis worries, however, that efforts to identify victims of slavery aboard fishing vessels are "only scratching the surface".
"I believe there's worse things happening," he said. "The ocean is so vast - and what happens there, none of us will know."
Authorities are trying to police another kind of criminal wreaking havoc on the seas - pirates.
While piracy has decreased worldwide in the past decade, the Gulf of Guinea off the coast of West Africa has become an increasing target for pirates who steal cargo and demand ransoms, according to the International Maritime Bureau (IMB).
Ships in or around Nigerian waters were the target of a series of piracy-related incidents last year, with 10 kidnappings involving 65 crew members, the IMB said in a report in January.
Crucial to protecting oceans as pressure mounts is understanding what lies at the bottom, experts say.
A U.N.-backed initiative, called Seabed 2030, is trying to do that by pooling data from around the world to produce a publicly available map of the entire ocean seafloor by 2030.
"Can you imagine operating on the land without a map, or doing anything without a map?" asked Larry Mayer, director of the U.S.-based Center for Coastal and Ocean Mapping, a research body that develops tools for underwater mapping.
"We depend on having that knowledge of what's around us - and the same is true for the ocean," he said.
The project initiated by the Nippon Foundation, a Japanese philanthropic organisation, and GEBCO, a non-profit association of ocean experts, aims to improve knowledge of marine biodiversity, predict disasters and protect deep-sea resources.
From underwater drones to crowdsourced data from fishing boats, new technology could drastically speed up the mapping process, researchers said.
"With advanced sonar technology it really is like seeing. I think we've come out of the era of being the blind man with the stick," said Robert Larter, a marine geophysicist at the British Antarctic Survey.
Advances in technology could also help in the fight against illegal, unreported and unregulated fishing, with theft estimated to be worth $23.5 billion a year, experts said.
A range of platforms are tracking fishing on the high seas and in marine reserves, aided by radio and satellite data that transmits vessel locations and movements, allowing authorities to identify illegal behaviour.
But political infighting is a roadblock in the way of data and knowledge sharing, said Julian Barbiere of UNESCO's Intergovernmental Oceanographic Commission, which is supporting the Seabed 2030 initiative.
Some countries are reluctant to share what they consider strategic data with the project, he said, largely due to national security concerns or because it comes from areas with sensitive geopolitical tensions, such as the disputed South China Sea.
But too much is at stake for countries to hoard data, he said.
"(It) goes back to this principle: the ocean is an international space by definition ... part of the common heritage of mankind," said Barbiere.