Traditional fishing destroys corals – new research

Traditional fishing techniques are destroying some of the world’s finest coral reefs, according to new research which has major implications for international marine conversation management strategies.

Until now commercial fishing was believed to pose the greatest risk to reefs, which are found in more than 100 countries and cover almost 300,000 square kilometres.

However, a British research team has found the comparatively minor disruption to the marine environment by subsistence fishing can bring disastrous consequences.

The scientists, from the Universities of Newcastle upon Tyne and Oxford, spent two years studying the impact of traditional fishing in Fiji, where they witnessed healthy corals dying and being rapidly replaced – possibly permanently – by algae.

Findings from the study, funded by the Natural Environment Research Council, are published in the current edition of the academic journal, Ecology Letters.

The research team focused on 13 Fijian islands where fishing was carried out at varying levels of intensity by locals using tools such as spears and hook-and-line.

They found even light levels of fishing caused populations of the coral-consuming crown-of-thorns starfish to grow because this removed the starfish’s predators, such as wrasses and triggerfishes, from the sea. They also found a clear correlation between the density of starfish, the amount of algae covering the reef and the degree of fishing activity.

For example, around the more heavily-fished islands, the researchers concluded that as starfish predators declined by almost two-thirds, starfish numbers rocketed from ten per kilometre to hundreds of thousands and healthy coral cover declined by a third.

On one island, where scientists tracked the starfish population explosion over one year, healthy corals began to rapidly disappear and in space of one year the cover of algae increased from one fifth of the reef to over half.

Lower population densities of starfish, a greater volume of healthy corals and a lesser covering of algae were reported in the more lightly-fished areas.

Although experts say the world’s coral reefs are disappearing as fast as its rainforests, until now little has been known about how fishing disturbs the reefs’ ecosystems.

Project leader Dr Nick Polunin, of Newcastle University’s School of Marine Sciences and Technology, said:

“Scientists previously thought diverse ecosystems such as coral reefs would be relatively resilient to the impacts of predator removal. This study suggests this may not be the case and that even low levels of fishing may cause ecosystem meltdown.

“We don’t know how permanent the damage is without further research but as we were observing changes over two years it seems as though it could be relatively long-term.

“The findings provide an additional challenge for biodiversity protection and coral reef management strategies.”

Research team member Dr Nick Dulvy, who carried out the field work, said:

“Exploitation of the seas, such as fishing, has resulted in a worldwide decline in predators. However, surprisingly little is known of the impact of removing predators on marine biodiversity.

“We were very surprised our research showed such light levels of exploitation by subsistence islanders fishing for food could cause such profound ecosystem changes.”

The crown-of-thorns starfish has long been recognised as a major threat to coral reefs, with population outbreaks occurring on Australia’s Great Barrier Reef for the last few decades.

The research team highlight that marine areas protected from fishing should maintain high numbers of predators. However Great Barrier Reef experience of repeated waves of the starfish indicates that only severe reductions in fishing activity are likely to prevent starfish infestations and the coral loss which follows across entire reef networks.