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A new study by The University of Western Australia and the University of British Columbia has found 437 million tonnes of fish worth an estimated $720 billion have been thrown overboard in the past 65 years globally by industrial fisheries using bottom trawls.

Bottom trawling captures fish through large nets that are dragged along the seabed by industrial vessels. The study,  published today in Fisheries Research, reveals bottom trawling generates the most fish losses.

Study co-author Professor Dirk Zeller, from UWA’s School of Biological Sciences and the Sea Around Us – Indian Ocean, said the huge waste of fish was due to the massive scale of bottom trawling involved and its lack of selectivity.

“Bottom trawl nets work by capturing everything, from deep-sea corals and sponges to perfectly good but unusable fish,” Professor Zeller said. “This is why a large amount of bottom trawl catch is thrown out and its lack of selectivity results in losses of non-targeted fish and a reduced value of the fish in markets worldwide.”

Professor Zeller said knowing how many fish each major type of fishing operation was removing, how much of that was brought to port, sold or used, and how much was discarded was crucial in evaluating the costs and benefits of fisheries.

“Small-scale fisheries use gillnets, traps, lines and hand tools and are responsible for only 23 per cent of the global catch – or approximately 1.3 billion tonnes in the past 65 years – but their catch is worth significantly more,” he said.

“By catching fewer quantities of higher-value species, such as crab and lobster, they actually made almost $260 billion.”

Tim Cashion, lead author of the study and researcher with the Sea Around Us initiative at the University of British Columbia, said industrial and artisanal (small-scale) fisheries had caught 5.6 billion tonnes of fish in the last six-and-a-half decades.

“Twenty-three per cent of that catch was captured by industrial bottom trawls, but industrial fisheries do not bring everything they catch to port,” Mr Cashion said. “During the period we studied, industrial fisheries threw out over 750 million tonnes of fish, and 60 per cent of that waste was due to bottom trawlers alone.

“Now we know with more certainty how much they are actually catching and landing, and how much of this they are discarding.”

The study highlights the importance of boosting well-managed artisanal fisheries, with the results showing that with very little infrastructure and support they already generated more value and less wastage of fish.

Media references

Jess Reid (UWA Media and Public Relations Advisor)(+61 8) 6488 6876