Crisis in global oceans as populations of marine species halve since 1970

Marine species around the world, including populations of fish critical to human food security, are in potentially catastrophic decline according to research published today. 

Great Barrier Reef (c) WWF
Great Barrier Reef. Image (c) WWF

Analysis by the Zoological Society of London (ZSL) of the population trends of marine species as presented in WWF's Living Blue Planet Report - an updated study of marine mammals, birds, reptiles and fish - shows a decline of 49 per cent in the size of marine populations between 1970 and 2012. As well as being disastrous for ecosystems, these findings spell trouble for all nations, especially people in the developing world who depend heavily on the ocean’s resources.

The findings are based on the Living Planet Index, a database maintained and analysed by researchers at ZSL. Following alarming statistics raised in the Living Planet Report 2014, revealing huge declines in vertebrate populations around the world, this special report studies how overfishing, damage to habitat and climate change are affecting marine biodiversity.

The analysis tracked 5,829 populations of 1,234 species, from sea birds to sharks to leatherback turtles, making the data sets almost twice as large as past studies.

Global food supply depleted

Many species essential to commercial and subsistence fishing – and therefore global food supply – are significantly depleted due to over fishing.  Global population sizes of the Scombridae family of food fish that includes tunas, mackerels and bonitos have fallen by 74 per cent.

Declining stocks of bluefin and yellowfin are of particular concern. Some species found in UK waters, including the vulnerable porbeagle shark and the critically endangered leatherback turtle, have also undergone precipitous declines. 

While over-exploitation is identified as the major threat to ocean biodiversity, the study finds that climate change is causing the ocean to change more rapidly than at any other point in millions of years. Rising temperatures and increasing acidity levels caused by carbon dioxide are further weakening a system that is already severely degraded through overfishing, habitat degradation and pollution.

Devastating figures

Professor Ken Norris, Director of Science at ZSL said:

"The ocean works hard in the background to keep us alive, generating half of the world’s oxygen and absorbing almost a third of the carbon dioxide produced from burning fossil fuels. It also feeds billions of people around the globe, some of whom rely solely on the oceans to survive. These devastating figures reveal how quickly human beings are changing the wildlife in our oceans and are a stark warning of the problems we might face as a result."

"My children loved Finding Nemo. This report suggests that billions of animals have been lost from the World’s oceans in my lifetime alone. If we don’t act now, we will face the very real possibility of explaining to our grandchildren why they are only able to find Nemo on the screen, not in the sea."

Dr Louise Heaps, Chief Advisor on Marine Policy at WWF-UK said:

"As well as being a source of extraordinary natural beauty and wonder, healthy seas are the bedrock of a functioning global economy.  By over-exploiting fisheries, degrading coastal habitats and not addressing global warming, we are sowing the seeds of ecological and economic catastrophe.  

“But there are clear steps that all governments can take to restore our oceans.  Creating networks of well-managed Marine Protected Areas is a proven way to enable wildlife and habitats to recover. Pushing for a strong global deal on climate change would help the seas sustain life far into the future. Taking serious steps to implement this year’s Sustainable Development Goals in the UK and abroad could help build a global economy that values natural capital, respects natural habitats and rewards responsible business.

“Every one of us can take meaningful action, starting today, by ensuring that all the seafood we eat is responsibly sourced and Marine Stewardship Council accredited. And as ocean stakeholders, we can call for governments and the private sector to invest in the recovery of our ocean so that we can benefit in the long-term from what it has to offer."

Coral decline could be catastrophic

The report also shows steep worldwide declines in the cover of coral reefs, mangroves and seagrasses that support fish species and provide valuable services to people.  It is very possible that we could lose coral reefs from most areas by 2050 as a result of climate change. With over 25 per cent of all marine species living in coral reefs and about 850 million people directly benefiting from their economic, social and cultural services, the loss of these reefs would be catastrophic.

The UK picture

It’s not all bad news in the UK. Recent assessments from the North Sea have shown that just over 50% of assessed stocks, including herring and haddock are being fished sustainably. Progress is being made in the designation of Marine Protected Areas, but the UK Government must do more to ensure delivery of a coherent and well-managed network of sites. Scotland has recently set a good example by proposing management measures that should ensure proper protection of sites. 

Current gaps in the network in England include seagrass sites - home to two species of seahorse - and protection for mobile species such as sharks, skates and rays, which are identified as being in trouble on a global scale in this report. 

What do you think should be done?

Share your views and follow the debate at: #StateoftheOceans.

Download the full report

ZSL's Indicators and Assessments unit

Our scientists are continuously tracking species numbers, and devising innovative new ways to gather the kind of data which formed the basis of this report. Find out more about their work here.

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