Deep sea stocks in decline

due to commercial fishing in the north-east Atlantic harming deep-sea fish populations a kilometre below the deepest reach of fishing trawlers, according to a 25-year study published on Wednesday.

According to Dr David Bailey of the University of Glasgow, who led the study  “Commercial fishing may have wider effects than anyone previously thought, affecting fish which we assumed were safely beyond the range of fishing boats. We were extremely surprised by this result and believe that it has important implications for how we manage the oceans.”

Populations of north-east Atlantic commercial deep-water fish such as black scabbardfish, orange roughy and roundnose grenadier have dwindled since deep-water fishing started in the area in the late 1980s and as unwanted species make up to 50% of the catch which all die when they are discarded, this explains why the study has shown a decrease in abundance of target and non-target species.

“Each deep-water species has a defined depth range and very often the juveniles live at depths shallower than the adults. Removal of fish by commercial trawling down to 1600 metres is likely to affect populations in deeper waters,” said Dr John Gordon of the Scottish Association for Marine Science and a member of the study team.

Fishery managers must now take into account adverse ecosystem effects, not just the abundance of the fish stocks being targeted and trawling may need to be restricted more than it is now and although there are plans for Marine Protected Areas in the north-east Atlantic they will need to be much bigger than the existing coral-protecting MPAs if they are to be effective.

“MPAs might not be as effective as we’d hoped since we can detect the depletion of fish up to over 50 miles outside the fishing zone,” added Dr Bailey.

“The general consensus is that deep-water fisheries are unsustainable and most if not all should be closed,” said Dr Gordon.

The study, funded by the Natural Environment Research Council, European Commission and the Marine Conservation Biology Institute, involved researchers from the University of Glasgow, the British Antarctic Survey, the Scottish Association for Marine Science, Highland Statistics and the University of Aberdeen’s Oceanlab.

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