TORONTO -- Low oxygen levels in the world’s oceans are threatening fish species and disrupting ecosystems, warn experts in a new report released at the UN climate conference in Madrid on Saturday.

As a result of increasing global temperatures and nutrient pollution, oxygen is declining in the oceans and coastal waters. That is threatening the livelihood of large fish species such as tuna, sharks, swordfish and marlin, the report found.

The larger fish are being forced to move toward shallow surfaces where there is more oxygen, but that leaves them vulnerable to overfishing, according to the report

In the largest peer-reviewed study done on ocean deoxygenation, scientists determined that there are now 700 ocean sites suffering from low oxygen. In the 1960s, there were only 45 ocean sites with low oxygen.

The report, titled “Ocean deoxygenation: Everyone’s problem”, was released on Saturday by the International Union for Conservation of Nature (IUCN) at the UN Climate Change Conference.

“Ocean deoxygenation is causing the loss biodiversity and loss of habitats,” Minna Epps, director of the Global Marine and Polar Program at IUCN, told CTV News Channel on Saturday. “The habitats are shrinking as species are fleeing these oxygen-deprived areas, but it’s also altering the energy and the biochemical cycling.”

The report, conducted by 67 scientists from 17 different countries, found oxygen levels in the world’s oceans declined by two per cent between 1960 and 2010.

“Two per cent may not sound like a lot, but there have been huge regional differences,” explained Epps. “Outside the southeast coast of California, in the deeper waters, we’ve actually seen a 30 per cent decline in oxygen levels over the last 25 years.”

The report indicates that under the status quo, the ocean is expected to lose three to four per cent of its oxygen by 2100.

“Climate change impact on oceans weakens its ability to provide services, whether it’s food, carbon storage or oxygen generation,” said Epps.

Co-author of the report, Dan Laffoley, is calling the findings the “ultimate wake-up call.”

“Ocean oxygen depletion is menacing marine ecosystems already under stress from ocean warming and acidification,” said Laffoley in an IUCN press release. To stop the worrying expansion of oxygen-poor areas, we need to decisively curb greenhouse gas emissions as well as nutrient pollution from agriculture and other sources."

Epps suggests reducing greenhouse emissions, investing in nature-based solutions that will help restore and protect the ecosystem and reducing non-climate change stressors such as overfishing as some actions that can be taken to prevent further damage and loss.

Officials from 200 countries are gathered in Madrid for the annual UN Climate Change Conference to discuss details of the Paris climate accord.

“The very decisions being made at the climate meeting in Madrid will determine the future of our oceans, whether it will continue to be oxygen-thriving ecosystem or if it will be irreversibly lost,” said Epps.