Marine protected areas produce more ‘trophy-size’ fish, UH report says: Big Island Now

Saltwater recreational fishing has cultural significance and is an important economic driver worldwide. PC: Tri Nguyen

Marine Protected Areas (MPAs) have a positive spillover effect, producing more “trophy-size” fish just outside fully protected areas, and the effect gets stronger over time, according to research led by scientists from the University of Hawaiʻi at Mānoa’s Hawaiʻi Institute of Marine Biology (HIMB), published in Science Advances. The study provides the first global assessment of the benefits of MPAs. “Trophy-size” refers to fish that are exceptionally long or heavy and are considered a rare, prized catch.

“This standardized global assessment illustrates the benefits that MPAs provide to recreational fishers, and confirms the effectiveness of MPAs in improving fish biomass and local fisheries,” said Simone Franceschini, the study’s lead investigator and a postdoctoral researcher at HIMB. “Our study found that MPAs can take more than 20 years to show tangible spillover effects into adjacent areas, which helps set realistic expectations about the timeframe in which a marine reserve can expect this kind of impact on surrounding fisheries.”

The Hawaiian archipelago has 13 state and federal Marine Protected Areas. The state protected areas, called Marine Life Conservation Districts, are managed by the State of Hawaii`i Department of Aquatic Resources.

Long-term expectations for MPAs

Conceptual illustration created using generative AI code in Python.

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MPAs have been identified as one of the most effective tools for securing marine biodiversity, but until now the global impact of MPAs on local recreational fisheries has been unclear. This study provides globally relevant guidance on what management agencies, conservation practitioners and, importantly, recreational fishers can expect from the establishment of MPAs in the long term.

The research builds on the work of scientists who conducted a study in Florida 20 years ago and found that the total number of trophy fish caught near a marine protected area (within 100 km of the border) increases rapidly between 12 and 30 years after the marine protected area is established.

“In this paper, we test whether the results of one of the best-known studies of the impact of MPAs on recreational fishers can be replicated at a global scale,” explains Elizabeth Madin, co-author of the paper and associate professor at HIMB. “We show that highly protected marine ecosystems on average deliver tangible, real, long-term benefits to recreational fishers, resulting in a win-win for both nature and people. Nevertheless, it is important to recognize that not every MPA will have the same spillover effects, and that successful MPAs rely on community support, enforcement, and effective fisheries management.”

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The findings of this study have important implications for the future of marine protected areas and the global marine conservation initiative “30×30”, which aims to protect 30% of the world’s oceans by 2030.

“These results provide evidence-based guidance that can help ensure the successful implementation and long-term sustainability of MPAs worldwide,” said co-author John Lynham, a professor of economics at UH Mānoa. “It is intriguing to note that different MPAs around the world, despite their different sizes and characteristics, have shown similar positive spillover effects and similar ‘wait times’: about 20 years.”

The study also highlights the importance of setting practical expectations about the benefits of marine reserves for local fisheries. While MPAs can lead to substantial increases in the abundance of large fish, the study shows that these benefits often require decades of patience and long-term policy to materialize. Nevertheless, as Callum Roberts, lead author of the original 2001 study on which the current study is based, notes: “Local fishers will see benefits to their catches from spillover of smaller fish long before that spillover becomes detectable in the form of large trophy fish, which take longer to reach record-breaking sizes. Well-protected MPAs can thus help to support local livelihoods within a decade of their creation.”