"With less than 10 percent of the ocean designated as MPAs (marine protected areas) and only 2.7 percent fully or highly protected, it is going to be difficult to reach the 30 percent target," said Lance Morgan, head of the Marine Conservation Institute in Seattle, Washington.

The institute maps the MPAs for an online atlas, updating moves to meet the 30 percent goal that 196 countries signed onto in 2022, under the Kunling-Montreal Global Biodiversity Framework.

The ambition is notably at risk because "we see countries like the US reversing course and abandoning decades of bipartisan efforts" to protect areas of the Pacific Ocean, Morgan said.

That referred to an April executive order by President Donald Trump authorising industrial-scale fishing in big swathes of an MPA in that ocean.

Currently, there are 16,516 declared MPAs in the world, covering just 8.4 percent of the oceans.

But not all are created equal: some forbid all forms of fishing, while others place no roles, or almost none, on what activities are proscribed or permitted.

"Only a third of them have levels of protection that would yield proper benefits" for fish, said Joachim Claudet, a socio-ecology marine researcher at France's CNRS.

Daniel Pauly, a professor of fisheries science at Canada's University of British Columbia, said "the marine protected areas have not really been proposed for the protection of biodiversity" but "to increase fish catches".

A proper MPA "exports fish to non-protected zones, and that should be the main reason that we create marine protected areas -- they are needed to have fish", he said.

When fish populations are left to reproduce and grow in protected areas, there is often a spillover effect that sees fish stocks outside the zones also rise, as several scientific journals have noted, especially around a no-fishing MPA in Hawaiian waters that is the biggest in the world.

One 2022 study in the Science journal showed a 54 percent increase in yellowfin tuna around that Hawaiian MPA, an area now threatened by Trump's executive order, Pauly said.

- Fishing bans -

For such sanctuaries to work, there need to be fishing bans over all or at least some of their zones, Claudet said. But MPAs with such restrictions account for just 2.7 percent of the ocean's area, and are almost always in parts that are far from areas heavily impacted by human activities.

In Europe, for instance, "90 percent of the marine protected areas are still exposed to bottom trawling," a spokesperson for the NGO Oceana, Alexandra Cousteau, said. "It's ecological nonsense."

Pauly said that "bottom trawling in MPAs is like picking flowers with a bulldozer... they scrape the seabed".

Oceana said French MPAs suffered intensive bottom trawling, 17,000 hours' worth in 2024, as did those in British waters, with 20,600 hours. The NGO is calling for a ban on the technique, which involves towing a heavy net along the sea floor, churning it up.

Governments need to back words with action, or else these areas would be no more than symbolic markings on a map, said the head WWF's European office for the oceans, Jacob Armstrong.