Bluestriped grunt and grey snapper in Hol Chan Marine Reserve off the coast of Belize

Pete Oxford/ILCP

Fish populations aren’t bouncing back in marine protected areas in the Caribbean Sea, according to a 12-year study. Poor enforcement of marine protection regulations, coastal development and rising water temperatures are probably to blame, say researchers.

The Mesoamerican Reef, which stretches more than 1000 kilometres along the Caribbean coasts of Belize, Guatemala, Honduras and Mexico, is home to a wide range of wildlife, including more than 500 species of fish and 65 species of coral.

Over the past few decades, the governments of these countries have put many marine protected areas (MPAs) in place with the aim of protecting the reef’s valuable biodiversity and restoring fish populations that have declined due to overfishing. These areas may ban fishing at certain times of the year, ban certain types of fishing equipment or restrict other activities such as tourism or mining.

To assess the effectiveness of these MPAs, Steven Canty at the Smithsonian Environmental Research Center in Maryland and his colleagues analysed changes in fish biomass between 2006 and 2018 for 111 protected sites and 28 unprotected sites. The data was collected in surveys by scuba divers as part of the Healthy Reefs Initiative.

The team found that just 11 of the marine protected areas saw increases in the biomass of adult fish over the study period, which tells us that their populations rose. Meanwhile, adult fish populations decreased in 28 of the protected sites, with the rest seeing no change. Unprotected sites saw a decline, but often less of decline than in the worst protected sites.

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At the 11 areas in which fish populations rebounded, the study found there was adequate enforcement of MPA regulations and fewer sea surface temperature fluctuations. Sites with poor recovery tended to see the opposite, with insufficient enforcement of protections, more coastal activity from people and more temperature anomalies.

“Enforcement plays a big part in how successful some of these areas are,” says Canty. He suggests that local people, whose livelihoods rely on adult fish, should be given a greater role in managing the MPAs. Ensuring that MPAs are placed in areas that are more shielded from climate change and easier to manage is also vital, he says.

“There’s still so much we don’t know about marine protected areas,” says team member Justin Nowakowski, also at the Smithsonian Environmental Research Center. “So being able to look to the past to optimise how MPAs are placed and managed in the future is critical.”

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