Deep-sea fisheries could benefit from a limit on deep-sea trawling in European waters to a depth of 600m – a ban suggested by researchers at the University of Glasgow and Marine Scotland Science.
The study, published in Current Biology, comes as the European Council considers controversial new legislation to manage deep-sea fisheries, including a ban on trawling below 600m.
Results from the research suggest trawling deeper causes greater damage for a reducing benefit to fishermen.
“The most notable thing to consider about our findings is that the trend in catch composition over the depth range of 600 to 800m shows that collateral ecological impacts are significantly increasing while the commercial gain per unit effort is decreasing,” said Joanne Clarke, a PhD student at the University of Glasgow.
Studies have already shown that deep-sea fish species are more vulnerable, due to the fact that individuals tend to live for a long time while having relatively few offspring in comparison to shallow-water species.
Research has also shown that deep-sea bottom trawling has taken its toll, with implications for the deep-sea ecosystem and for the climate. Deep-sea fish hide away large amounts of carbon per year.
Researchers used data from trawl surveys collected between the depths of 240m and 1,500m in the northeast Atlantic to look at changes in catch composition trends with depth. Those surveys used different gear types at various locations between 1978 and 2013.
An analysis of the data revealed a clear transition in catches at depths of 600m to 800 metres, including a significant increase in biodiversity, the ratio of discarded to commercial biomass, and the ratio of sharks and rays to commercial biomass. As the ecological impacts increased, the commercial value per unit of effort decreased.
“Depth limitations are often labelled as a ‘blanket’ measure, unsophisticated and poorly thought out,” Ms Clarke explained. “In this case, however, it appears that there would be some very specific conservation benefits to a depth limit at around 600m.”
“We had no prior reason to expect that our findings would suggest an appropriate depth. We went into this analysis to test whether any depth appeared particularly suitable for a depth limit, but with no expectation that this would be the case,” she added.
European Council discussions on the matter are expected to begin again in September and, while there are many other factors at play, the researchers say they are “very confident that the work will be brought to the attention of the relevant people and at a critical time”.
