Fish populations -- a staple source of protein in many parts of the world -- are being decimated by over-fishing, but a new study Thursday said the trend can still be reversed.

For the first time, researchers assessed some 10,000 large and small-scale fishing spots around the world -- the sources of around 80 percent of fish caught in the world.

In the past, data had been collected only for the largest and most valuable fish stocks: "a tiny slice that can give us a skewed view," said researcher Steve Gaines, from the University of California at Santa Barbara in a statement.

Thanks to the new assessment, researchers confirmed the unfortunate worldwide trend: populations are declining in more than 60 percent of fishing spots -- meaning the marine creatures are being harvested faster than they are being replenished by new hatchings.

But the study showed that the populations haven't reached the point of no return -- and that monitoring them seems to be crucial in turning things around.

The authors write that conservation measures, in particular, preventing overfishing, could help the populations recover and bring them back to sustainable levels.

That would mean more fish available for human consumption over the long term -- in some cases up to twice as many fish brought to shore as would be the case otherwise.

"For most fisheries, we simply didn't know how many fish were out there and whether their populations were trending up or down," said lead author and economist Christopher Costello.

"It's like trying to decide how far you can drive your car without knowing how much gas is in the tank."

The research showed that fish populations were similar around the world, whether or not they had been previously tracked.

But the two groups are trending in opposite directions: the ones being monitored are starting to improve, while, under current fishing pressures, fish populations elsewhere are "plummeting at alarming rates."

"The good news here is that it's not too late," explained Costello, though he said fixing the situation will require changes.

"The longer we wait, the harder and more costly it will be to bring these fisheries back. In another ten years, the window of opportunity may have closed."