A study carried out by BirdLife International, which has headquarters in Cambridge, England, reported 47 percent of 346 reviewed species are known or suspected to be in decline.
Seabirds constitute a small proportion of the world's bird species, just 3.5 percent, but researchers say they are an important indicator of the health of the oceans.
"They are top predators in their marine systems," John Croxall, head of BirdLife's Global Seabird Program, told the BBC.
"The fact that almost a third are globally threatened should really be telling us something about how we need to look after where they occur to breed on land and where they go to feed in the ocean."
Conservationists said they are particularly concerned about the albatross family, where 17 out of 22 species are threatened with extinction.
Commercial fishing is one of the key threats to seabirds, with large numbers killed in nets and on lines, they say, while invasive species such as rats and feral cats are threatening breeding colonies, either damaging habitats or eating chicks and eggs.