Commercial fishing in the north-east Atlantic could be harming deep-sea fish populations a kilometre below the deepest reach of fishing trawlers, according to a 25-year study undertaken by a consortium of research institutes.

Scientists concluded that commercial fishing may have much wider effects than previously thought, reducing fish populations and changing deep-water communities which were assumed to be safely beyond the range of fishing boats.

Commercial fishing in the north-east Atlantic could be harming deep-sea fish populations a kilometre below the deepest reach of fishing trawlers, according to a 25-year study undertaken by a consortium of research institutes.

Scientists concluded that commercial fishing may have much wider effects than previously thought, reducing fish populations and changing deep-water communities which were assumed to be safely beyond the range of fishing boats.

Researchers compared the abundance of deep-sea fish in two different periods, using data collected from 1977-1989 (before the commercial fishery for deep-sea species took off) and from 1997-2002. They unexpectedly found that deep-sea fish numbers down to 2500 metres - a kilometre below the deepest reach of fishing trawlers - were lower in the later 1997 to 2002 period. Not only this, but target species and non-target species were both affected and in much deeper parts of the ocean.

The decrease in population numbers was highest for those species whose range at least partially fell within fishing depths, and no other natural factors could be identified which would justify such a decrease. Each deep-water species has a defined depth range and very often the juveniles live at depths shallower than the adults. In addition to that, adults are known to move between deeper and shallower waters. Removal of fish by commercial trawling down to 1600 metres is thus likely to affect populations in deeper waters.

The deep-seas fishery targets relatively few species, such as roundnose grenadier and orange roughy, and unwanted species are discarded. These can make up around 50 per cent of the catch and because of the extreme change in pressure and temperature when they’re brought to the surface, none of these will survive. This explains why the study has shown a decrease in abundance of target and non-target species.

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, but it wasn’t until 2003 that catch quotas were recommended.

According to the researchers’ press release, “Fisheries 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”.

While the OSPAR Convention is considering plans for Marine Protected Areas (MPAs) in the north-east Atlantic, researchers fear that this might not be enough. MPAs might not be as effective as previously hoped unless fleet fishing effort is limited in the surrounding areas.

This study, published in the journal Proceedings of the Royal Society B., adds to the growing body of evidence indicating that deep-water fisheries are unsustainable and underlines Seas At Risk’s view that most if not all of these fisheries should be closed.

Press Release

Royal Society Article

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