Whitetip reef sharks, Pacific creolefish, barberfish, and Moorish idols populate a reef in the Revillagigedo Archipelago. Credit: Enric Sala, National Geographic Pristine Seas
Researchers have used cutting-edge satellite technology to reveal that the most highly protected zones are deterring illegal fishing despite industrial fishing vessels continuing to sneak into marine protected areas (MPAs) worldwide.
The findings of 2 new studies published in the journal Science suggest that MPAs can curtail industrial fishing given proper investment and regulation, and that emerging satellite technology can be a key tool to monitor and enforce them more effectively.
The first study focused on 455 MPAs within the exclusive economic zones of coastal nations. These were categorised as “highly protected” and “fully protected” and explicitly prohibit industrial fishing.
The authors analysed data from the Automatic Identification System (AIS) which tracks individual vessels. Signals are transmitted to shore-based receivers and satellites in real time, and machine learning algorithms analyse them to predict when boats are actively fishing.
However, AIS has its limitations: not all vessels are required to use it, AIS is unreliable in areas with poor signal reception and it can be tampered with to evade detection.
So, the researchers turned another source of intel: synthetic aperture radar (SAR) imagery collected by the Sentinel-1 satellite constellation.
“SAR actively detects vessels by sending radar pulses to the ocean surface and measuring the reflected signals,” they write in the study. “Machine learning algorithms then identify vessels from these reflectance patterns and classify them as fishing or non-fishing vessels. These algorithms detect most industrial vessels – those longer than 15m – regardless of whether their AIS is active.”
AIS data missed almost 90% of SAR-based fishing vessel detections.
“No single dataset can solve the challenge of monitoring fishing activity at sea; each has its blind spots,” says co-author Juan Mayorga, a marine data scientist with National Geographic Society’s Pristine Seas and the University of California, Santa Barbara, USA.
“By fusing AIS tracking with satellite radar imagery and AI, we are now much closer to the full picture of human activity across the ocean.”
Sharks and fish swim beneath the ocean’s surface at San Benedicto Island. Credit: Enric Sala, National Geographic Pristine Seas
Their analysis suggests that little unauthorised fishing occurred in most MPAs over the 5-year study period (2017 to 2021): “On average, these MPAs had just one fishing vessel present per 20,000 square kilometres during the satellite overpass, a density 9 times lower than that of the unprotected waters of exclusive economic zones.”
“Because strictly protected marine areas discourage illegal fishing, fishes are far more abundant within their boundaries, they produce many more babies, and help replenish surrounding areas,” says co-author Dr Enric Sala, conservationist and founder of Pristine Seas. “In other words, the fishing industry benefits from following the rules.”
However, Professor Boris Worm of Dalhousie University in the US, who was not involved in the research, says MPAs with this level of protection account for less than 10% of them all.
The second study took advantage of the same SAR dataset and deep learning models but analysed fishing activity in 6,021 MPAs with a wider range of protections. The authors detected industrial fishing vessels in 47% of them between 2022 and 2024.
“Furthermore, fishing effort (measured as the number of fishing hours) in the protected areas was often at a level equal to or greater than that observed in nonprotected areas nearby,” Worm writes in a related perspective published in Science.
He adds that these results are “partially consistent” with the findings of the first study, as fishing effort was lower in more strictly protected areas.
“However, further analysis … suggests that the presence of industrial fishing patterns in MPAs is more strongly related to the size and remoteness of the protected area, rather than to their management category per se.”
Less than 1% of the ocean was formally protected in 2000. This figure rose to 8% in 2025. Worm suggests the differences in the studies’ findings may be partially explained by the efforts to rapidly expand MPAs.
“Many MPAs have been established quickly without strong protective regulations, meaningful consultation with local stakeholders, or appropriate management capacity,” writes Worm.
“In some cases, this has resulted in ‘paper parks’ that are recognised as protected areas but do not prevent harmful activities. These observations have important implications for ongoing efforts to expand MPA coverage to at least 30% of the ocean by 2030.
“Clearly, paper parks will only ever deliver suboptimal outcomes, if any at all. The available data show that where proper investments are made, industrial exploitation is curtailed, and protective measures are comprehensive, long-term benefits will accrue.”
Technology like SAR will allow nations to better predict the locations of illegal fishing and more efficiently target patrol efforts.