Scientists assigned a grade for global ocean health on Tuesday, giving the world's waters a "D" on an annual oceans report card, citing overfishing, pollution, climate change, and lack of protections as key problems.

But the score for nations' territorial waters—generally those that are within 200 miles (322 kilometers) of shore—has improved since 2012, and scientists say the overall outlook for the ocean is better than many expected.

The latest report card is part of the third annual update to the Ocean Health Index, which evaluates the state of the seas and the benefits they provide to people.

"This new assessment is the first fully global look at ocean health," said Kevin Connor, a spokesperson for Conservation International, an environmental group that prepared the index with help from researchers from the University of California, Santa Barbara; the University of British Columbia; the New England Aquarium; and others.

For the first time, this year's index measures scores for Antarctica and the Southern Ocean plus the 15 other ocean regions beyond national jurisdiction, often called the high seas. The overall global score was 67 out of 100. (See "New Ocean Health Index Measures the Global State of the Seas.")

"I think many people are surprised that the score is that good, because people hear all the bad news about overfishing, pollution, death of coral reefs, climate change, and so on," said Conservation International's Steve Katona, who serves as managing director of the Ocean Health Index.

"If you come home with a paper from school, your parents aren't real happy if it's a 67, but most people expected a score for the ocean that was worse," he said.

Scoring the Ocean

In arriving at their scores, researchers evaluated ecological, social, economic, and political factors for each region, then crunched the data through a computer model. A score of 100 does not necessarily mean a perfectly pristine ocean, but rather that the ocean is able to sustainably provide benefits like oxygen and food.

One goal of the index is to help countries make more informed policy decisions about the ocean, said Katona. China, Colombia, and Israel have all incorporated information gleaned from their particular score into their coastal management programs. Chile, Peru, and Canada may follow suit, according to Katona.

The combined score for the territorial waters of all countries and territories that have them was also 67 out of 100. That's up from the 2012 score of 60 and the 2013 score of 65. The U.S. scored 72 this year, compared with 63 in 2012. China scored 65, up from 53 in 2012.

Antarctica scored a 72, while the overall score for all of the high seas was 67. Although Antarctica is largely undisturbed, little of its coastline is technically protected, Katona said. Further, fishing pressures and climate change have taken a toll on animals there, including southern bluefin tuna, basking sharks, Gentoo penguins, and several species of albatross.

The eastern central Atlantic and western Indian Ocean scored best among the high seas, each receiving a score of 79. The Arctic scored a 54 and the northwest Pacific scored a 53, at the low end, largely due to heavy fishing and lack of protections.

"The high seas do a lot of good for people," said Katona. "They regulate climate, generate oxygen, provide food, and contribute to a sense of place."

Evolving Science

Katona said one reason the overall scores ticked up since 2012 was because conservation measures have been gaining some ground and slowing some of the decline that has occurred since the preindustrial era. New marine protected areas have also "made a big difference," he said.

The expansion of the Pacific Remote Islands Marine National Monument, announced by the Obama administration last week, happened too recently to be incorporated into the index, but it should make an impact in the future, Katona added.

Another reason scores have risen: Scientists changed the way they measure the impact of fisheries. Instead of calculating a score based solely on catch data from fishers, the index now measures those values against what scientists estimate would be the optimal biomass of the fish that would provide a maximum sustainable yield.

The new data suggest that overfishing has been less severe in some areas than previously thought, although it is still a problem in many places.

Another change provided additional information on the benefits that the ocean provides for tourism. The previous Ocean Health Index looked only at international arrivals in countries as a proxy for tourists, but the new version looks at the number of workers in the tourist sector in a given area. As a result, scores for tourism tended to rise.

The Ocean Health Index was begun in 2008 and first published in 2012, with funding from National Geographic and other partners. National Geographic did not contribute to this latest update.