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Fish Numbers Diagnose Coral Reef Health

13 April 2015

AUSTRALIA - The number of fish living on coral reefs can be used as a test of reef health to inform sustainable fishing decisions, according to new research from Dr Aaron MacNeil and colleagues.

An international team of marine scientists surveyed more than 800 coral reefs worldwide to develop the test.

Dr MacNeil said: "By studying remote and marine protected areas, we were able to estimate how many fish would be on a coral reef without fishing, and how long it should take newly protected areas to recover.

"This allows us to gauge the impact of reef fisheries, and make informed management decisions that include timeframes for recovery."

Coral reefs are home to thousands of species of fish and provide food and income for millions of people, particularly those in the developing world.

However, the scientists found that the vast majority of fished reefs they examined have lost more than half of their fish.

Marine reserves are the most effective way to recover fish populations, however, there are no benchmarks to determine if the protection is effective, or whether a reserve has recovered enough to be fished again.

To solve this problem, the team studied the fish biomass on coral reefs around the world and discovered that near-pristine reefs contain 1,000 kilos (a tonne) of fish per hectare.

Using this figure as a benchmark, they found that 83 per cent of fished reefs have lost more than half of their fish biomass.

From their work the scientists were able to determine that once protected, previously fished reefs take about 35 years to recover, while heavily depleted reefs take almost 60 years.

Co-author Dr Nick Graham said it was encouraging to find that substantial biomass remained where some form of management was in place.

"Changes in fishing practices can result in a significant return of key fish species over time.

"Restrictions on types of gears, species caught, or local customs, all ensured substantial recovery in fish feeding groups.

"However, only completely closed marine protected areas successfully returned large predatory fish to the ecosystem," he said.

Dr MacNeil said that fisheries managers have the potential to arrest a key threat to coral reefs.

"Where previously we have been managing reef fisheries not really knowing how depleted fish stocks were, we now have a roadmap for recovery that tells us not only where we are with fish biomass, but where we might want to go, and how long it will take to get there."

Further Reading

You can view the full report and author list by clicking here.

TheFishSite News Desk

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