More than 40% of the world's fishing is carried out unsustainably and largely in defiance of international codes of conduct, according to a new study. The team that carried out the research said that voluntary schemes to prevent overfishing should be replaced with binding international laws that can better protect marine ecosystems.

Leatherback turtle hatchlings. Australia on Sunday listed the world's largest sea turtle, the leatherback, as endangered due to the threats posed by overfishing and the unsustainable harvesting of its eggs and meat (AFP/File/Jimin Lai) Scientists graded the 53 major fishing nations - those that take 96% of the world's marine catch - on how their intentions matched actions in complying with the UN's code, a voluntary measure developed in 1995 as a potential way to tackle overfishing.

The code sets out criteria on how countries should implement the right type of equipment for how fish are caught and how to minimise ecosystem impacts such as catching unwanted fish species that have to be thrown back into the sea and minimising effects on dolphins and other mammals.

Norway comes top of the list with a compliance rate of 60%, followed by the United States, Canada, Australia, Iceland and Namibia.

In the bottom 28 countries, representing more than 40% of the world's marine fish catch, the compliance rates were so poor that the authors gave them "fail" grades, meaning they complied with less than 40% of the UN code of conduct. Twelve countries in this category also failed in all or most sections of the compliance analysis. The UK is ranked 14th.

The work, carried out by Tony Pitcher and Ganapathiraju Pramod of the fisheries centre at the University of British Columbia in Cabnada, Daniela Kalikoski at the Federal University of Rio Grande in Brazil and Katherine Short at WWF International in Switzerland, is published in the journal Nature tomorrow.

Giles Bartlett, WWF's fisheries policy officer, said he was surprised by the low scores of countries that are thought to have the most progressive fishing policies. "We know the global oceans are in crisis but I thought that the highest-scoring countries would score higher than they've done. That shows the challenge is pervasive - not just in the high seas but in areas we consider to be the best-managed in the world such as Australia, New Zealand, Iceland and Canada."

Overall, the five questions on which countries scored worst concerned introducing ecosystem-based management, controlling illegal fishing, reducing excess fishing capacity and minimising bycatch and destructive fishing practices.

The authors wrote that new international rules were needed to address overfishing. "Although the voluntary nature of the code may have been necessary in getting all-nation agreement when it was drafted in the early 1990s, attitudes to the oceans have changed," they said.

"There is now widespread scientific consensus on the ecological impacts of continued overfishing and the threats to seafood security, and broad agreement on policy issues such as curtailing illegal catches and minimising the impacts of fishing on marine ecosystems. The time has come for a new integrated international legal instrument covering all aspects of fisheries management."

Bartlett said that the next reform of the EU's common fisheries policy, due in 2012, had the potential to tackle some of the problems. "The last reform was going to adopt ecosystem management as a fundamental principle but it hasn't delivered on that," said Bartlett. "[They should] look at the best systems in the world in terms of governance such as Australia, where they've changed the emphasis of fisheries management to keeping ownership of resources to the industry. This means the industry doesn't have the incentive to overfish, the incentive is to look after the resource."

Other management systems include setting up marine reserves. "You can look at how humans use the sea and look at how humans mitigate those impacts, be they fisheries impacts or oil and gas exploration. Marine reserves are the best tool for mitigating those impacts on the ocean."

"The United Kingdom comes out 14th below Namibia and South Africa and only just above Malaysia," said independent fisheries biologist Doug Herdson. "What is most surprising is the spread of the European Union nations 10th to 31st when all are supposed to be following a 'common fisheries policy'. It can certainly be argued that things have been changing in the four years since the majority of this study was carried out; most notably the EU's maritime strategy, its discards policy, and the UK's marine bill, though none of these is yet in effect."

He added: "The global problem is the mindset that economic necessity must override everything else, and consequent failure to recognise that no economic measure can succeed if it is not supported by a sustainable environment. Despite recent studies showing the degradation of marine ecosystems, we have not yet outgrown the 19th-century concept that the seas are endlessly bountiful."