Do Shark Sanctuaries Really Protect Sharks? It depends.

Shared spaces, different strategies

Shark sanctuaries are a widely promoted large-scale conservation tools for sharks.

They typically ban commercial shark fishing and the trade of shark products across national waters, sometimes covering entire Exclusive Economic Zones.

At first glance, the logic is simple: If you stop targeted fishing, shark populations should recover.

But the reality is more complex.

What this study actually does

In “A global evaluation of shark sanctuaries” (Global Environmental Change), we examined 15 shark sanctuaries across the Atlantic, Indian, and Pacific Oceans.

We combined diver-based observations with information on human use patterns, fisheries pressure, and reported shark populations, and compared these with non-sanctuary regions.

The goal was to understand whether sanctuaries change the underlying pressures on sharks—and how those changes vary across locations.

What the study shows

Across sanctuary countries, we consistently found reduced direct fishing pressure on sharks and fewer reports of sharks being sold in markets compared to non-sanctuary regions. In several cases, shark population declines also appeared less pronounced than in nearby non-sanctuary areas. This suggests a clear effect on one of the primary drivers of shark mortality: targeted exploitation.

However, the pattern is not uniform across all sanctuaries or all threats.

What sanctuaries do—and do not—address

While shark sanctuaries restrict directed fishing and trade, they do not automatically address other major sources of shark mortality.

Across study regions, we continued to observe:

• bycatch in non-target fisheries

• ghost gear and lost fishing equipment

• marine debris

• habitat degradation in coastal systems

These pressures operate outside sanctuary regulations and often determine overall mortality levels just as much as directed fishing.

Variation across sanctuaries

Not all sanctuaries performed the same way.

Some showed strong reductions in fishing pressure and clearer conservation signals. Others showed more limited differences compared to non-sanctuary regions, where implementation or enforcement appeared weaker or less consistent.

This variation points to an important distinction: designation alone is not the same as implementation.

Why this matters for shark populations

Shark populations are shaped by multiple overlapping pressures. Even when directed fishing is reduced, bycatch and habitat-related impacts can continue to influence trends. This means sanctuary effects cannot be interpreted in isolation from broader fisheries and ecosystem management. In practice, sanctuaries interact with existing governance systems rather than replacing them.

The key insight: protection depends on the full pressure landscape

This study shows that shark sanctuaries reduce a specific subset of pressures—mainly targeted fishing and trade—but do not address all drivers of mortality.

Their effectiveness depends on how they interact with:

• fisheries management outside sanctuary rules

• bycatch mitigation measures

• enforcement capacity and

• monitoring of actual shark populations

Without these elements, outcomes vary substantially across regions.

Why this matters for management and conservation

Shark sanctuaries are often treated as a standalone solution.

But this work suggests they function more like one layer within a broader management system.

This has direct implications for:

• fisheries policy and bycatch regulation

• marine spatial planning

• international trade enforcement and

• conservation performance assessment

Evaluating sanctuaries requires looking beyond policy presence to actual changes in pressure and population indicators over time.

What changes now

This work reinforces a broader shift in ocean management: from assuming policy designation equals protection to measuring how policies change real-world pressures.

Within this framework, sanctuaries become part of a larger adaptive system that depends on monitoring, evaluation, and iterative improvement.

Tools that integrate multiple data streams—such as diver observations, fisheries data, and spatial monitoring—can help track whether changes in pressure are translating into changes in shark populations over time.

Frequently asked questions

Do shark sanctuaries stop shark fishing completely? They eliminate directed commercial shark fishing in principle, but enforcement and compliance vary by region.

Do they reduce shark populations declines? In some cases, yes—threats appear less severe in sanctuary regions, but results vary across countries.

What threats remain inside sanctuaries? Bycatch, ghost gear, marine debris, and habitat degradation remain key sources of mortality.

Are sanctuaries enough on their own? They reduce targeted pressure, but broader fisheries and ecosystem management are also required.

What is the main takeaway? Shark sanctuaries reduce specific pressures, but outcomes depend on how they are implemented and what other management measures are in place, and the threats sharks face.

Final thought

Shark sanctuaries change one part of the system. Whether they protect and rebuild shark populations depends on the nuances.

Read the full study

Published in GLOBAL ENVIRONMENTAL CHANGE:
A global evaluation of shark sanctuaries