Sea beds take years to recover from bottom trawling, say scientists reports 20th July 2017: Trawling the bottom of the ocean can strip up to 41% of invertebrate life from the sea bed, and ocean floors can take more than six years to recover.

Globally, around one-quarter of wild-caught seafood comes from bottom trawling, but the impact of this type of fishing has been unclear.

Jan Geert Hiddink at Bangor University, UK, and his colleagues combined data from 70 studies around the world to model the ecosystem damage of trawling.

‘Otter trawls’, which use heavy boards at the front of nets to plough up the sea bed, were the least harmful, removing around 6% of bottom-dwelling invertebrates.

Most damaging were hydraulic dredges, which use high-pressure water to stir up animals for harvesting. These removed 41% of invertebrates.

Recovery from losing 50% of an area’s biomassbiomass The amount of living matter. This is therefore a different measure to numbers of organisms. So, for example, there is much more biomass in 1 elephant than there is in 1000 fleas and there may be more biomass in 100 large cod than you would find in 150 small (because of over fishing) cod. to trawling takes between 1.9 and 6.4 years, according to the authors’ model.

Combining the model with maps of trawling frequency will allow the assessment of this type of fishing on unprecedented scales, say the authors.


Marinet observes: Bottom trawling has long been observed to be a most damaging form of fishing, destroying the biota upon which fish and the local ecosystem depend. Nevertheless, few restrictions originating from governmental quarters apply to it. Voluntary restraint by fishermen is rare. A very clear example of the ecological meltdown caused by bottom trawling is the experience of the Firth of Clyde, Scotland, documented by Dr. Ruth Thurstan and Prof. Callum Roberts.

The situation is made worse when trawling is repeated continuously. Trawling of the same spot often occurs more than once a year, and is frequently repeated year after year. The result is the severe damage reported by the Bangor University study, and in extremis by the R. Thurstan and C. Roberts study.

If the UK takes control of its fisheries following exit from the EU, and especially in light of the recent announcement by the UK Government that exclusive control is to be re-established out to 12 nautical miles, then the future of UK fisheries will greatly depend on their management by the UK Government. Will this embrace restrictions on bottom trawling in order to rebuild and sensibly harvest fish stocks?

This is a major unanswered question at the present time.


Source:, 20th July 2017. For further details, see


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