Fishermen returning from the sea with their catch. Zanzibar Island. Tanzania

Cape Town - WWF’s Living Blue Planet Report has highlighted enormous losses in the world’s oceans – but this was not just about “losing some fish and turtles”, according to John Tanzer, director of WWF International marine programme.

“It is about the unravelling of the fabric of an ecosystem that sustains life on Earth.”

Tanzer said while Nasa’s photos taken from space in 2015 showed the same blue planet that Nasa had captured in 1972, “we know the planet has changed substantially and perhaps irrevocably in the intervening four decades”.

The report, released every two years, gives a current picture of the state of the oceans, and according to WWF’s director-general, Marco Lambertini, it shows how humanity is “collectively mismanaging the ocean to the brink of collapse”.

Lambertini said within a single generation, people had severely damaged the oceans, both by catching fish faster than they could reproduce and by destroying fish nurseries such as estuaries, seagrass meadows, mangroves and corals.

Marine populations globally have dropped by more than half in the last 40 years, and deep-sea fish populations in the North Atlantic have dropped by a massive 72 percent.

The report measures trends in 10 380 populations of 3 038 species of marine mammals, birds, reptiles, amphibians and fish. These populations have declined by 52 percent between 1970 and 2010.

Tuna, mackerels and bonitos show a decline of 74 percent between 1970 and 2010. There is no sign of their recovery.

Researchers looked at three marine species – sharks, turtles and sea cucumbers – as they were good indicators of the level of stress on marine ecosystems.

In the Galapagos, sea cucumbers had declined by 98 percent from 1993 and by 94 percent between 1998 and 2001 in the Red Sea. Sea cucumbers, regarded as a delicacy in many areas, play a vital role in marine ecosystems, and researchers found some areas without sea cucumbers had become uninhabitable for other organisms.

Global catches of sharks and rays had risen more than three times between 1950 and 2003. One of four species of sharks and rays are threatened with extinction, mainly from over fishing. Sharks are apex predators, and the loss of apex predators will cause degradation of the ecosystem.

Four turtle species are categorised as endangered or critically endangered.

More than 25 percent of all marine species live in coral reefs – and 75 percent of coral reefs are threatened, and could be lost altogether in 35 years. About 850 million people directly benefit from coral reefs, which provide food for hundreds of millions.

Seagrass meadows, which provide food and protection for many species, including fish that are commercially important, have declined by 30 percent over the last 100 years. Seagrass is also vital for storing carbon and can store more than twice as much as a forest.

Nearly 20 percent of mangroves – or 3.6 million hectares – were destroyed between 1980 and 2005, mainly to build harbours and infrastructure, and for agriculture and tourism.

Marine and coastal zones have been damaged by mining. While no commercial deep-sea mining operations have occurred yet, the International Seabed Authority has issued licences covering 1.2 million square kilometres of ocean floor.

The report said while the impacts from this type of mining were unclear, the huge areas of seabed that had been licensed, could cause impacts that were “unprecedented”.

Lamberti said considering the vital role oceans played in world economies, the mismanagement of the oceans was “simply unacceptable”.

Cape Times