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When commercial fishers haul up their nets, they often find dolphins, sharks, sea turtles, and other creatures entangled amid their catches. These accidentally caught, nontarget species are known as by-catch, and millions of animals worldwide are killed this way each year. A significant proportion of these trapped animals are seabirds—ocean-adapted species including gulls, albatrosses, and cormorants.

Seabirds are among the most threatened bird groups in the world, with nearly one-third at risk of extinction. In a new study, a team of ecologists compiled and analyzed by-catch reports from across Europe and estimated that almost 200,000 individual birds are caught and killed in European waters annually.

The researchers also broke down the data by species, family, fishing practice, and region. They found that the top three species caught as by-catch are common guillemots, northern fulmars, and northern gannets. The three bird families particularly vulnerable to fishing are ducks, auks, and procellariids (which includes petrels and shearwaters). Endangered species such as common eiders and Balearic shearwaters are also regularly found as by-catch.

In Europe, gillnets and longlines entangled the highest number of avian by-catch. Graphic by Mark Garrison and Marina Wang, with data from Ramirez et al.

Among fishing practices, two methods stood out as especially deadly: gillnetting and longlining. With gillnetting, fishers hang panels of nets in the water column, which often entrap plunge-diving birds with poor vision, including auks and sea ducks. In longline fishing, ships drag 40-kilometer-long lines with baited hooks behind their boats. The bait and hooked fish attract birds, such as albatrosses and petrels, which can get caught and drown.

Researchers think they’ve probably underestimated seabird by-catch as the data they compiled had gaps in timing and geographic region. But, according to the team, there’s enough data to show that coastal EU countries are failing to adequately protect seabird populations, resulting in serious costs for vulnerable species.