Bombs, cyanide and trophic cascades: When fishing gets out of hand

“A continuous series of corals, sponges, sea anemones, and other marine productions, of magnificent dimensions, varied forms, and brilliant colors. In and out moved numbers of blue and red and yellow fishes, spotted and banded and striped in the most striking manner, while great orange or rosy transparent jellyfish floated near the surface …The reality exceeded the most glowing accounts I had ever read of the wonders of a coral sea.”

Such were the words of British explorer Alfred Russel Wallace on his voyage through the Malay archipelago in 1869. The region is home to the most diverse ecosystems of the marine domain—coral reefs, created by thousands of years’ worth of work by minute organisms that extract calcium carbonate from the water and deposit this as solid limestone. By doing so, corals—and certain types of algae—have built colossal structures that give home to a diversity of organisms rivaling that of the Amazon rainforest.

This diversity sustains the lives of some 500 million people across more than 100 nations with coastlines fringed by coral reefs. These ecosystems are an indispensable source of fish and seafood and also critical breeding, feeding and nursery grounds for many open-ocean fish, notably tuna. They’re invaluable to medical research, harboring organisms with anti-cancer or AIDS-inhibiting properties, and to tourism, being the producers of the fine, white coral sand of tropical beaches. Together with mangrove forests they form fortresses that protect entire coastlines from waves, storms and floods.

But today, nearly 150 years after Wallace described them in their pristine state, the ‘rainforests of the ocean’ stand at the brink of ecological ruin. Increasingly crowded coastal populations are exhausting the once thriving fish stocks. According to a study published earlier this year in Nature, nearly nine in ten reefs have lost at least half their natural fish numbers. Particularly the most desirable fish—which tend to be large, predatory ones—have shown devastating population crashes, often crossing the threshold at which they are capable of regenerating.

Equally alarming are the knock-on effects of the decimation of these species. The coral reef food web is an ancient, carefully balanced network in which the loss of any one player can cause a domino effect that reverberates through the whole system.

For instance, the heavy exploitation of species that predate on sea urchins has had disastrous effects on Kenyan reefs: These particular sea urchins feed on crustose coralline algae, which—like corals—are critical to reef formation. In the absence of their predators, they were able to proliferate to extreme abundances, wreaking havoc over the reef by eroding away its foundation. This enabled other types of algae that are typically harmful to corals to thrive and dominate the reef. This effect was exacerbated by the overfishing of herbivorous fish species that usually graze on them. By comparison, non-fished reefs in marine parks remained healthy, where sea urchins and algae were kept in check by intact fish communities.

Screen Shot 2017-03-30 at 10.00.08

Kenya: Overfishing of invertebrate predators and herbivorous fish can lead to overgrowth of algae.

All unsustainable fishing has negative impacts on fish stocks and has the potential to throw the ecosystem out of kilter via such ‘trophic cascades’ – where the removal of a predator causes an increase in the numbers of its prey. However, because we don’t know exactly how reef food webs work—and each one may have evolved differently—, they are near impossible to predict.

Tragically, the last three to four decades have seen the rise of a number of destructive fishing practices that further exacerbate the situation. Desperate as ever to ensure their income despite dwindling stocks, many fishers have resorted to a variety of highly destructive fishing methods: Bottom trawling, spearguns, explosives and cyanide have had catastrophic impacts on coral reefs through their alarming potential to not only capture vast amounts of fish with little effort, but also to kill many other species and destroy the reef-building framework.

In Indonesia—the world-leading exporter of ‘ornamental’ fishes—cyanide is used to capture colorful reef fish for the aquarium trade or display in restaurants—supposedly stunning the fish without killing them. Many fish die regardless and surviving ones tend to have shorter lifespans. A non-selective respiratory poison, cyanide can severely damage any reef organisms it comes into contact with, including corals.

Also, bombs made from artificial fertilizers or illegally sourced dynamite are thrown upon schooling reef fish, which are killed and then collected by divers. A single beer bottle bomb can obliterate all life within an area of around 20 square meters and shatter the delicate skeletons of live corals, turning them into dead rubble.

Screen Shot 2017-03-30 at 10.00.19.pngIn Southeast Asia, nearly 95% of reefs are affected by overfishing and destructive fishing practices.

Most reefs today would appear unrecognizable to Wallace, their fish stocks drained, their food webs knocked out of balance, bombed, poisoned. These impacts make it all the more difficult for reefs to cope with the effects of coastal pollution, rising sea levels and global warming.

If current rates of destruction continue, it is estimated that 60% of reefs will be destroyed over the next 30 years, with devastating consequences for the lives depending on them for food, income and coastline protection.

According to the aforementioned study in Nature, completely banning fishing on reefs could restore the ecosystems to a robust state within 35 years. However, burgeoning populations and increasing poverty and hunger in developing reef nations make this strategy unfeasible.

Hope lies in communities that have succeeded for generations in maintaining a balance between fishing and keeping their reefs in good health. By enforcing seasonal fishing bans to give the fish time to spawn and breed, whilst condemning the use of destructive fishing practices, traditional peoples of Kenya and Raja Ampat, Indonesia, set an example that could lead the way into a sustainable future for reef fisheries. Perhaps one day, coral reefs will recover to their natural state – bursting with the color and life that Wallace so admired.

 

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