01/19/2016 12:41 EST | Updated 01/19/2017 00:12 EST

Ocean fish catches 50% higher than reported, study suggests

Humans are scooping millions of tonnes more fish out of the oceans than official statistics show — about 50 per cent more, estimates a new Canadian study that sheds some light on the extent of the problem and on who's catching all those extra fish.

Statistics compiled by the Food and Agriculture Organization of the United Nations (FAO) and cited by the study show that global marine catches between 1950 and 2010 peaked in 1996 at 86 million tonnes before declining by around 0.38 million tonnes per year.

But by scouring out and including unreported catches around the world, the new study by Daniel Pauly and Dirk Zeller at the University of British Columbia and their 400 global collaborators with the Sea Around Us project estimates that the peak catch in 1996 was actually 51 per cent higher — 130 million tonnes, and has been declining by 1.2 million tonnes a year.

The FAO statistics are based on numbers reported by individual countries, based on their own statistics, which include mainly industrial fishing catches.

'Systematic underestimation of catch'

"Countries have the bad habit of reporting only what they see," Pauly said a teleconference organized by Nature Communications, the journal that published the study today.

If they don't have the data for certain types of fishing, they report that zero tonnes are caught by that method.

"The result of this … is a systematic underestimation of catch. This can be very high," Pauly added — up to 20 to 30 per cent in developed countries or up to 200 to 300 per cent for some smaller island states.

"Here we show that the main trend of the world marine fisheries catches is not one of 'stability' as cautiously suggested earlier by FAO, but one of decline," the researchers wrote in their paper. "Moreover, this decline, which began in the mid-1990s, started from a considerably higher peak catch than suggested by the aggregate statistics supplied by FAO members, implying that we have more to lose if this decline continues."

But that's not entirely bad, Pauly said, because it means the oceans are more productive than thought and conservation and good fisheries management may have better results than anticipated.

"If we rebuild stocks, we can rebuild to more than we thought before," he said.

But the shortcomings of the FAO statistics are a challenge for international groups like the World Health Organization that rely on them to guide the development and implementation of projects.

"They are the ones who suffer most from this information being false, being misleading," Pauly said in an interview with CBC News.

"Unreported fisheries have an enormous impact on the stocks in countries where they operate."

The study suggests that all UN databases should be periodically evaluated "to ensure they avoid producing poor numbers."

Canada's cod problem

In this case, the missing catch includes fish caught by a lot of small-scale or "artisanal" fisheries, subsistence fishing, sport fishing and illegal fisheries.

"Because we're dealing with states, you can't say, you have an illegal fishery in the country, even if everyone knows it," Pauly said.

It also includes "bycatch," fish that are caught inadvertently and dumped by fleets targeting other species, such as shrimp. That was found to be a problem for the Atlantic cod off Canada's East Coast, and one of the factors preventing the stocks from recovering for many years, despite a moratorium on commercial fishing since 1992.

"Lots of small cod were being thrown away," Pauly said. "To the cod, it doesn't matter whether they're targeted or not."

One stock, the Northern cod, was recently found to have made a good recovery, but not enough to resume fishing, and recovery for other stocks is still years away.

The new study summarizes some of the findings of 200 smaller studies by 400 collaborators in countries around the world. Researchers from those countries looked for specific gaps in local catch data and tried to fill them. About a third of those studies have been published in peer-reviewed journals so far, Pauly said, while the rest — including the Canadian one, are considered papers in progress.

"For every country, there was a peculiar story to find and it was found," Pauly said.

For example:

- In one island in the Pacific, catch statistics included only tuna, but people were known to eat coral reef fishes. The researchers managed to get data about that from local anthropologists or aid workers.

- In the Bahamas, a UBC PhD student who was from there originally, managed to get information about small-scale fisheries by going to hotels and getting their invoices from those who sold them fish.

- Illegal fishing catches were estimated from the size of fishing boats spotted in certain areas.

- Subsistence catches were estimated based on local fish consumption statistics.

The Sea Around Us project has been largely funded by the Pew Charitable Trusts and the Paul G. Allen Family Foundation.