Predatory reef fish 'nearly wiped out' across Caribbean coral reefs


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Black grouper in a reef at Dry Tortugas in the Florida Keys. Images courtesy Abel Valdivia/Centre for Biological Diversity.

Sharks and other predatory fish are scarce across Caribbean coral reefs due to decades of overfishing.

But several coral reefs throughout this region offer ideal conditions for fish recovery — if they are protected from human impacts, researchers found.

The study by scientists at the Centre for Biological Diversity, the Smithsonian Institution and the University of North Carolina at Chapel Hill — found that while up to 90% of large reef-fish predators are absent from most Caribbean reefs, several ‘super sites’ should be priorities for conservation due to their high recovery potential.

“Predatory reef fishes have nearly been wiped out, but we can bring them back with smart conservation measures,” said Abel Valdivia, a marine ecologist with the Centre for Biological Diversity. “If fishing is eliminated or reduced and effective protection is put in place, some of these reefs could support unbelievable abundances of predatory fishes. We called them super sites.”

The researchers analysed 39 coral reefs inside and outside marine protected areas across the Bahamas, Florida, Cuba, Mexico and Belize and estimated the biomass of all reef fish species at each location for three years. The study also identified the best combination of environmental and biological factors to forecast large predatory fish biomass in the absence of fishing. The authors measured coral abundance and other reef features known to influence large predators, as well as variables such as coastal development, human population density and enforcement of fishing regulations.

“It is unbelievable how uncommon most large predators in coral reefs are today, especially near large human population centres,” said Courtney Cox of the Smithsonian Museum of Natural History. “Only at a handful of sites across the entire Caribbean could we see large groupers and reef sharks. When you see them, they are very wary of your presence and quickly disappear. Most reefs with big fish predators are inside well-enforced marine reserves, which attract a large number of tourists every year.”

Today large predatory fishes are more abundant within fishing-prohibited marine protected areas than unprotected reefs or sites with inadequate fishing regulations. But the biomass of predatory fishes that coral reefs can support depends on specific environmental conditions and prey availability — the carrying capacity of a particular system. This means that the recovery potential for fish at each reef varies across space and time.

Marine reserves are the most commonly used management strategy to protect reef fish from fishing, and studies show they can rapidly increase fish abundance in as little as five to 10 years. Such areas also boost local economies by promoting tourism and eventually local fisheries. But even at the best-enforced marine reserves, illegal fishing is still occurring. Practices like shark feeding make large predators vulnerable to poaching when they leave fishing closures.

“Over their long lifespan, a live reef shark or huge goliath grouper is worth millions of dollars in revenue to the local tourism industry because thousands of people travel to these locations just to see these creatures,” said John Bruno, a professor of marine conservation at the University of North Carolina. “Just imagine if we can effectively protect these super sites that offer ideal conditions for predatory fishes. I believe that in less than a decade we could see a substantial increase in large predators and with them local economic growth.” 

The study is published in the journal Science Advances.