Banning demersal trawling would lead to higher CO2 emissions as consumers switch to more protein produced on land, according to a new scientific paper.
Writing in the ICES Journal of Marine Science, researchers agree that demersal trawling can be highly destructive when not managed well, but when stocks are overfished, this is usually due to poor management.
The scientists led by Prof Ray Hilborn at the University of Washington and involving researchers at Heriot-Watt and Bangor universities used relative benthic status to measure the impact of trawling on the seabed.
Demersal trawls generally have higher levels of bycatch and discarding, but there have been improvements in the selectivity of gear over the past two decades.
A global assessment of relative benthic status showed very different levels of impact of trawling around the world, with severe levels in parts of the Mediterranean while the Irish Sea and west of Scotland are not quite so damaged.
Australia, Southern Chile and the Gulf of Alaska were the least depleted.
The authors agreed that areas with sensitive habitats like deep water coral should be closed to trawling, as these species can take decades or centuries to recover.
In a review of data from “whole lifecycle” assessments of different foods, they found that an average kilo of bottom-trawled fish produces 4.65 kg of CO2. While this is double the carbon footprint of chicken (2.28kg), it is one quarter the footprint of beef (19.2kg).
They point out that well-managed fisheries have lower fuel use, citing Alaskan pollock, the world’s largest whitefish fishery, as one example. It produces just 0.83kg of CO2 for every kilo of food, and the authors attribute this to enlightened fisheries management.
The authors note that catching fish in the ocean “uses no pesticides or fertilizer, almost no fresh water, and no antibiotics”.
“The global impacts from these would be increased if bottom trawling was banned and/or agriculture or aquaculture increased to compensate, although there are significant differences in these impacts among cropping systems,” it says.
The authors conclude that banning all demersal trawling would not be good for the planet if it drives consumers to another animal protein with a higher carbon footprint. They recommend improving management rather than introducing widespread bans.
The full paper is here