Do Marine Protected Areas Really Help Fisheries?

from Saving Seafood, Nov 22, 2024

November 22, 2024 -- Marine Protected Areas (MPAs) are often promoted as tools to conserve fish populations and improve fishing yields. However, a recent study, "When does spillover from marine protected areas indicate benefits to fish abundance and catch?" by Ray Hilborn, Mark Fitchett, John Hampton, and Daniel Ovando, published in the journal Theoretical Ecology, questions whether MPAs consistently benefit fisheries as assumed.

What is Spillover?

“Spillover” refers to the movement of fish or larvae from MPAs into fishing zones, which is thought to enhance fish abundance and catch rates nearby. While gradients in fish density—higher populations near MPA boundaries—are often observed, the study finds that these patterns do not always mean fisheries are improving.

Using computer models and case studies, the authors determined that spillover benefits are most likely in areas where fishing was intense before MPAs were established. In regions with lower fishing pressure, MPAs generally had minimal impact on total fish populations or catches.

Findings of the Study

Fishing Pressure Matters: MPAs are most effective when fishing pressure has been high. In such cases, closing areas can allow fish stocks to recover, increasing overall abundance and sometimes catch rates.

Large MPAs and Migratory Fish: For highly mobile species like tuna, large MPAs, such as the Papahānaumokuākea Marine National Monument (PMNM) in Hawaii, showed limited benefits. The study found little evidence that the PMNM increased tuna populations or catches, as much of the area was lightly fished even before its closure.

Not Always a Fishery Benefit: The presence of a gradient—more fish near MPA borders—does not necessarily indicate increased total fish abundance or improved catches.

Examples Explored

South Africa: MPAs in South Africa demonstrated clear fishery benefits, with increased catches linked to spillover. These areas had been overfished, creating conditions where MPAs could help.

Papahānaumokuākea Marine National Monument: Despite being one of the world’s largest MPAs, the PMNM showed no significant fishery benefits for tuna. The closure displaced fishing effort but did not noticeably increase tuna populations or catches.

Conclusion

Spillover happens when fish or larvae move from protected areas into fishing zones, often leading to higher fish populations near MPA boundaries. While this is commonly assumed to benefit fisheries, the study found that these increases in abundance do not always mean more fish are caught or that total populations grow. Only areas with intense fishing pressure before the MPA’s establishment showed clear benefits to fisheries. For large, open-ocean MPAs, the study found little evidence of positive effects on tuna populations.

Author Affiliations

Ray Hilborn: School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, USA
Mark Fitchett: Western Pacific Fisheries Management Council, Honolulu, Hawaii, USA
John Hampton: Pacific Community, Noumea, New Caledonia
Daniel Ovando: Inter-American Tropical Tuna Commission, La Jolla, California, USA

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