There’s a saying that goes, “There’s plenty of fish in the sea”. But with seafood a vital source of protein for almost 4.5 billion people worldwide, what do we really know about the sustainability of the seafood on our dinner plates?

Here are 10 key facts about global fishing that explore how much our food supply relies upon the health of the ocean.

1. How many fishing boats are at sea?

In 2014, there were an estimated 4.6 million fishing vessels worldwide. Asia accounted for 75 percent of the global fleet, followed by Africa (15 percent), Latin America and the Caribbean (6 percent), North America (2 percent) and Europe (2 percent).

2. How many tons of fish are caught every year?

Roughly, 109 million metric tons of fish are caught every year. Scientists say the global fish catch peaked in 1996 at 130 million metric tons, and has been declining ever since.

3. Which countries are the top exporters of fish?

The top five exporters of fish are China, Norway, Vietnam, Thailand and the United States.

4. Which countries are the largest importers of fish?

The U.S. imports the most seafood, followed by Japan, China, Spain and France.

5. What is the condition of global fish stocks?

Scientists estimate that 85 percent of the world’s fisheries are fully exploited, overexploited, depleted or being fished at biologically unsustainable levels.

In practical terms, this means that we are taking fish out of the sea much faster than the remaining fish can reproduce and replace their populations.

6. What are the major causes of overfishing?

Poor fisheries management, illegal fishing, bycatch of marine species, unsustainable fisheries subsidies and fishing practices that destroy marine habitat.

7. How much seafood is harvested illegally?

Illegal, unreported, and unregulated (IUU) harvests are significant contributors to the depletion of fish stocks. Experts estimate that between 11 and 26 million metric tons of fish annually are caught illegally, equivalent to between 14 and 33 percent of the world’s total legal catch.

The total monetary value of current IUU fishing losses worldwide are between U.S. $10 billion and $23.5 billion annually.

8. How much of fish capture is certified as sustainably harvested?

In 2015, 9.4 percent of global wild catch was certified by the Marine Stewardship Council as being harvested at “maximum sustainable yield,” or MSY.

MSY is a widely recognised benchmark that represents the largest catch that fishers can harvest from a particular fish stock without depleting it.

9. How many people depend on artisanal fisheries for food or income?

Artisanal fisheries are small-scale harvests for local subsistence or small markets. They are vital to livelihoods and food security, particularly in developing nations. Artisanal fisheries typically use traditional techniques and small boats.

While artisanal and commercial fisheries each harvest the same amount of seafood for human consumption, 27 million metric tons, artisanal fisheries employ 25 times more fishers (over 12 million people), and use an eighth of the amount of fuel annually as that burned by industrial fisheries.

10. Which marine species are most heavily fished?

These ten species account for about 27 percent of the world’s ocean fish harvest:

Alaska pollock: 2.9 million metric tons a year

Peruvian anchovy: 2.8 million metric tons a year

Skipjack tuna: 2.7 million metric tons a year

Sardinellas nei: 2.1 million metric tons a year

Pacific Chub mackerel: 1.6 million metric tons a year

Atlantic herring: 1.4 million metric tons a year

Yellowfin tuna: 1.33 million metric tons a year

Scads nei: 1.32 million metric tons a year

Atlantic Mackerel: 1.28 million metric tons a year

Japanese anchovy: 1.26 million metric tons a year

Photo: NOAA Fisheries