The future of seabed mining in the Pacific is set to remain contentious, with cultural and environmental campaigners continuing an ongoing debate over the controversial practise.

An ocean scientist has concluded not enough is known about seabed mining to decide whether deep-sea mining surrounding the sovereign waters of the Cook Islands could well be environmentally sustainable ahead of plans for the small Pacific island to approve the activity.

The Cook Islands' Seabed Minerals Authority returned last week from a 21-day deep-sea research expedition on board the United States exploration vessel EV Nautilus, which the National Oceanic and Atmospheric Administration, an American scientific and regulatory agency, has separately funded.

High-resolution imagery and data was collected in a bid to better understand what lives on the ocean floor.

Cook Islands Seabed Minerals Authority knowledge management officer, Dr John Parianos, a technical director with government authority in charge of seabed minerals, says the findings are set to guide future decisions on the mining process.

"One day someone will have to make a decision about what to do and it's so clear we don't know enough to make a decision," he said.

The practice of seabed mining involves the collection of polymetallic nodules from the bottom of the sea, with mineral concretions forming concentric layers of iron and manganese hydroxides at its core.

As nodules are found in vast quantities and contain valuable metals, deposits can well be identified as a potential benefit to several Pacific Island economies.

However, the Nautilus expedition was said to have focused on discovery and the chance to test new deep-sea technology.

The expedition's success relied on the testing of a new, ultra-high-resolution camera, the MxD SeaCam, designed for deep-sea research at depths of up to 7000 metres.

The camera combines a compact broadcast camera with custom-built titanium housing to capture 4K images with definitive clarity.

Dr Parianos said captured content is some of the best footage ever recorded several kilometres below the surface and would help create the Cook Islands' first-ever public catalogue of deep-sea life.

"We've benefited from probably the highest resolution images ever taken at these depths in the whole world ever," he said.

"We need to make a catalogue of the types of life in the Cook Islands seabed, so that way researchers in the future can reference it."

Expedition lead on the Nautilus, Renato Kane, said bad weather threatened its mission, however it improved in time to utilise a remote, manoeuvrable underwater device to explore the ocean's depths.

"We've had six really successful dives to the sea floor," he said.

"We're diving these vehicles down to over 5000 metres depth and the length of these dives were on average, about 30 hours each.

"So, we've got a lot of high-definition video footage for scientific observation."

On its return to the shore from its lengthy scientific research, EV Nautilus was confronted by a group of kayakers holding signs that read: "Don't mine the moana".

Louisa Castledine, a prominent protester on the scene, told Radio New Zealand she is conscious the National Oceanic and Atmospheric Administration along with the vessel had a reputation for being "environmentally friendly", but remains concerned about research being "weaponised".

"This research is being used to help enable and guide decision making towards deep-sea mining," Ms Castledine, who is the spokesperson for Ocean Ancestors, a conservation ocean advocacy group, said.

"It's the guise in which this research is being utilised, and it's who sent them that is the challenge because who sent them is quite clear on their intent in mining."

The US and the Cook Islands governments agreed to work closer in the area of seabed minerals to "advance scientific research and the responsible development of seabed mineral resources" back in August of this year.

It came off the back of the Cook Islands signing a five-year agreement with the People's Republic of China to cooperate in exploring and researching seabed minerals.

Ms Castledine, who resides in the Cook Islands (Kūki 'Airani), said the region is in the middle of a "geopolitical storm", with the US and China vying for control over deep-sea minerals.

"The USA's building their military might within the Pacific and this is one of those ways in which their reach is moving more into the Pacific and more specifically into Cook Islands waters," she said.