Matthew Mulrennan was trying to find and film the elusive colossal squid in Antarctica when his underwater footage revealed something worrying in the deep.
The footage revealed a sea floor scoured of life with "deep grooves" that suggested damage by anchor chains.
"You could clearly see this delineation between where there was abundant marine life and where the chain and anchor had disrupted the sea floor," Mr Mulrennan said.
It is the first video evidence of environmental damage in the sensitive polar region, Mr Mulrennan and colleagues report today in the Frontiers in Conservation Science.
An estimated 4,000 species live on the Antarctic sea floor, with around 90 per cent unique to the southern continent's waters.
Mr Mulrennan said most visitors might go there for the penguins, seals and whales, but the region's biodiversity was more like an iceberg.
"Almost all of it is underwater," he said.
"[The] animals that are there are very vulnerable. Some grow to extreme years of age including giant volcano sponges, which we found right next to the anchor damage."
Mr Mulrennan, a marine scientist and founder of not-for-profit conservation group Kolossal, was on a tourist ship visiting Antarctica in 2023 when he took the footage.
Concerned about what he saw, he contacted marine geophysicist and anchor chain damage researcher Sally Watson from the New Zealand National Institute of Water and Atmospheric Research.
Dr Watson confirmed the linear grooves and harsh gouges, recorded in the popular destination Yankee Harbour next to an Antarctic island, were consistent with damage caused by anchors and their chains.
Mr Mulrennan and Dr Watson said the findings raised concerns about anchoring by research and fishing vessels, as well as a growing tourism industry in Antarctica.
They said more regulation and collecting of anchoring data was needed ahead of a projected quadrupling of tourists to 452,000 people a year visiting Antarctica by 2033–34.
How do anchors damage the oceans?
Anchors can be metres wide, and crush the living things they land on, but it's the chain connecting the anchor to the ship that often does the most damage as it drags laterally across the sea bed.
Many Antarctic seabed animals grow slowly in the same place over centuries, making them vulnerable to chains.
Dr Watson said anchor chains probably had the second biggest impact to the sea floor after trawling by commercial fishers.
Research into anchor impacts is growing in places such as the Great Barrier Reef and other tropical reef environments but Dr Watson said there was a "big gaping hole" in Antarctica.
Mr Mulrennan surveyed 36 sites around the Antarctic Peninsula, and anchoring damage was only found at the Yankee Harbour site.
[map]Dr Watson wasn't able to access voluntary anchoring data kept by the International Association of Antarctica Tour Operators (IAATO), so she used ship tracking data to estimate anchoring activity instead.
Eight vessels likely used their anchors in Yankee Harbour during the month Mr Mulrennan surveyed the area.
Dr Watson estimated a minimum of 1,600 metres of seabed would be affected if each vessel anchored in water 30–40 metres deep.
This figure does not consider the damage from the chain dragging side to side if the ships moved.
"We don't know the footprint of anchoring within the Antarctic Peninsula, so it could be a pretty extensive issue for the sea floor," Dr Watson said.
Social scientist Elizabeth Leane of the University of Tasmania, who was not involved with the study, said there were sites more popular than Yankee Harbour that hadn't been surveyed.
Professor Leane, whose work focuses on Antarctic tourism, noted Cuverville Island and Neko Harbour received more visits than Yankee Harbour.
Tourism operators to examine research
Lisa Kelley, the executive director of IAATO, said the group welcomed "research into all forms of human activity in Antarctica".
"We acknowledge that this study represents a snapshot in time," Ms Kelley said."The insights provided will be shared with IAATO's relevant committees and working groups to support our ongoing commitment to safe and environmentally responsible operations in the Antarctic region."
Greg Mortimer, who founded the Antarctic tour company Aurora Expeditions, said operators had become more aware of potential damage caused by anchors since the 2000s.
He said tourist ships were able to visit Antarctica based on their impacts being less than minor or transitory.
"If that's not the case, further action is needed," Mr Mortimer said.
He said the "missing link" was knowing how much damage was being done and its significance.
Dr Watson said collecting more data on anchoring, as well as surveys of marine life, will be crucial to planning sea-floor-safe Antarctic tourism.
What could be done?
Mr Mulrennan said ships at times already operated safely in Antarctica without using an anchor.
When sea ice is high, vessels cannot get to water shallow enough to drop anchor and rely on dynamic positioning systems — where a vessel uses its own propulsion — to stay put.
Dr Watson said she recognised it wasn't possible to get rid of anchoring entirely.
"I want to be really clear about the difference between anchoring when you have a storm, and you're trying to protect the people and ship, compared to cruising up to a harbour and dropping anchor willy-nilly," she said.
"I think it's really important to not have a blame game in this space because this is a regulation system problem … if we know better, we can do better."
In areas of high destruction, Mr Mulrennan suggested operators could agree on "parking lot areas" where all visiting ships anchor or that moorings be created in high traffic zones.
Parking lots were a "sound idea" according to Mr Mortimer, who said most ships anchored in the same place anyway.
However, he believes moorings would be vulnerable to Antarctica's extreme weather and iceberg damage.
Professor Leane said she was hopeful tour operators would take the research on board and come up with solutions.
"[Tourist operators] don't want a damaged environment as people are increasingly interested in seeing the undersea environment," she said.
