Are marine protected areas working? Satellites reveal the truth

Marine protected areas (MPAs) are showing real impact, not just promises. A large-scale global study proves that strong legal bans on industrial fishing in fully and highly protected MPAs are effective.

Despite perceptions that poaching is common due to weak enforcement, the evidence now shows otherwise.

Researchers examined 1,380 MPAs that prohibit industrial fishing. Across these areas, the average presence of vessels was one per 20,000 square kilometers during satellite flyovers. That is nine times less than in unprotected zones.

This gap highlights the strength of legal protection when backed by data and technology.

Satellites reveal hidden fishing boats

The study combined data from Automatic Identification Systems (AIS) and Synthetic Aperture Radar (SAR). AIS provides signals from vessels, while SAR detects ships even when they try to stay hidden.

Machine learning models processed five billion AIS signals and thousands of SAR images.

SAR revealed vessels in MPAs where AIS showed nothing, especially in Southeast Asia. It also confirmed the absence of industrial fishing in 91 MPAs. This shows that SAR fills AIS blind spots and adds accuracy.

In many cases, even MPAs with detected vessels had fishing on fewer than 3% of imaged days.

Most areas had minimal fishing

The bulk of fishing effort came from a few well-known MPAs. The Chagos Archipelago saw around 2,700 hours of fishing annually.

South Georgia, the South Sandwich Islands, and the Great Barrier Reef Marine Park each had around 900 hours per year.

Other sites like Camargue in France, Cape Canyon in South Africa, and Marado Island in Korea recorded 275 to 450 hours.

However, most MPAs showed no or minimal activity. About 78.5% of them recorded less than one day of fishing per year, and over 1,000 had no detected activity.

Fishing is no longer unchecked

To compare differently sized MPAs, researchers used fishing effort per 100 square kilometers.

The highest density was in Marado Island at 18 hours per day per 100 square kilometers. Yet the global average across all MPAs was only 0.0004 hours per day. That is nearly negligible.

Some of the high-effort areas are small, so even a few vessels skew the density. For instance, Korean MPAs with only 2 km² imaged showed high density, but just 6 to 18 total vessels were detected.

These findings help correct public perceptions that industrial fishing remains unchecked.

Most fishing zones are quiet

The analysis builds confidence in MPA protections. The radar detected no vessels in 25% of MPAs.

In those with activity, vessels appeared on just 3% of imaging days. Also, SAR found vessels in 163 MPAs where AIS showed nothing, proving its critical role.

“The ocean is no longer too big to watch. With cutting-edge satellites and AI, we’re making illegal fishing visible and proving that strong marine protections work,” said Juan Mayorga, co-author and scientist at Pristine Seas.

Why marine protected areas seem weak

Many still believe MPAs are just legal statements on paper. That view stems from two issues: weak regulations and poor enforcement.

Some MPAs legally allow industrial fishing or only exist as designations with no real action. Others are difficult to patrol.

But this new research solves an old puzzle. It focuses only on MPAs with the strictest bans and uses implementation dates, not just legal designations. This avoids errors where fishing occurred before rules took effect.

The study also reduces confusion caused by phaseout periods, such as the five-year gap in Palau’s marine sanctuary.

Some fishing slips into protected zones

While protections work, they are not perfect. Some activity may reflect legal exceptions or data errors. For example, certain fleets had sunset provisions allowing temporary fishing.

Small-scale fishing, often legal, can also affect ecosystems but remains mostly invisible to SAR if vessels are under 15 meters long.

“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,” said Enric Sala, co-author and founder of Pristine Seas.

Results may not apply everywhere

One key question remains: Are MPAs truly reducing fishing, or were they placed in low-activity zones? The paper suggests both might be true.

Of the few MPAs with pre- and post-implementation data, most already had low fishing. Yet Palau showed a dramatic drop from 51,000 hours to just 215 hours annually after full protection. That suggests strong rules can reduce fishing pressure even in active areas.

Future MPA planning should consider whether protections are going where demand to fish is already low. Otherwise, the results may not scale as hoped.

Marine protected areas work

The study proposes a scalable way to monitor oceans. Integrating real-time satellite detections with AI models offers an efficient, low-cost solution.

The research supports the idea that MPA enforcement creates deterrence. The more likely vessels are to be caught, the less likely they are to fish illegally.

“By using satellites to track fishing vessels, countries can predict the locations of illegal activities and target patrol efforts, saving both manpower and money,” said Jennifer Raynor, lead author from the University of Wisconsin-Madison.

The study is published in the journal Science.

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