As the European Parliament considers a ban on deep-sea trawling, a new study documents the destruction of marine life from such fishing practices.

“Species in the deep sea are long-lived and reproduce slowly, so they are particularly vulnerable to exploitation,” said Joanne Clarke, a doctoral student at the University of Glasgow in Scotland and coauthor of the study, which was published Thursday in the journal Current Biology.

Clarke, who wanted to determine if the proposed ban on trawling below 1,968 feet would be effective, analyzed data from surveys taken at different depths at various locations between 1978 and 2013.

She and her colleagues discovered that fishing at depths greater than 1,968 feet magnified the accidental death, or bycatch, of fish not targeted by trawlers. Deep-sea sharks and rays were particularly hard hit, with some populations declining by up to 90 percent in North Atlantic waters.

The researchers found that the ratio of cast-off animals to commercial fish significantly increased at greater depths, ranging from three discarded ones for every 100 fish caught at 1,968 feet to 160 for every 100 fish at a depth of 4,200 feet.

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“We weren’t expecting to find that the ratio of discards to commercial fish increases so much with greater depths,” said Clarke.

The scientists also discovered that fish biodiversity increased at lower depths, with 18 more species for every 300 feet.

Even though there were more species present, only 80 were commercially viable, according to the study, indicating that it may not be worth the expense to fish at such depths.

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Clarke said the methodology used in this study could help researchers and policy makers craft more effective fishing regulations.

“The deep sea is full of really interesting species, and we are still learning a lot about them,” she said. “Just because you can’t see something doesn’t mean you shouldn’t be interested, and we should consider that when thinking about exploiting the deep.”