The next time you cook a fish or order some seafood at a restaurant, think about the image above.

It’s a snapshot of all the fishing happening on the ocean over a six-month period. If you zoomed in, you’d see thousands of blue dots, each showing one instance of likely fishing activity at one point in time. This image captures almost 20 million hours of commercial fishing by tens of thousands of vessels around the world. As we approach World Oceans Day this week, it’s sobering to reflect on the fact that industrial fishing now occurs in more than 55% of the ocean – an area more than four times bigger than all the land used for farming.

The vast majority of fishing vessels follow the rules governing fishing – but many are not, and these bad actors can cause a lot of damage.

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Vessels may take too many fish ­– overfishing – which is causing our fisheries to collapse. Then there is the problem of illegal fishing, which can occur in protected areas, in another country’s waters or on the high seas. Many countries simply don’t have the capacity to enforce fishery management rules. As a result, illegal fishing has become a multi-billion-dollar industry, worth up to $23bn each year. Because of overfishing – both legal and illegal – one third of fisheries assessed in a study by the UN Food and Agriculture Organisation were overfished and over half were fully fished. This threatens jobs and food security for millions of people, all around the world.

The trouble is, so much of this illegal activity is hidden – it happens out to sea, making it difficult to scrutinise what individual vessels are getting up to. To address the problems facing our oceans, we need to know what’s happening beyond the horizon.