The world's supply of seafood -- the major protein source for nearly one in six people -- could be gone by 2048 if current trends continue, according to a new study published in the journal Science.
The U.S. seafood industry disputes the study's findings, however, and said it is already taking action to ensure that popular choices like swordfish are available to consumers well into the future.
The study found that ocean fish, seafood and plant species that had already "collapsed" had reached 29 percent in 2003, up from about 13 percent in 1980.
"This trend projects that there will be 100 percent of species collapse by the year 2048," said Boris Worm, a biologist at Dalhousie University in Halifax and lead author of the study.
Stresses on the ocean, such as overfishing, destruction of habitat, pollution and even global warming reduce the ability of marine animals to survive, say experts.
"Fisheries in many parts of the world are in bad shape," said Joshua Reichert, director of the environment division of the Pew Charitable Trusts, an environmental advocacy organization.
"Each year it's estimated that human beings remove approximately 150 million tons of life from the sea. And what's clear is that the global marine environment cannot sustain that kind of loss," said Reichert, who was not connected with the study.
Much of the blame, said experts, lies with the unregulated use of massive bottom trawling nets in 67 million square miles of ocean -- an area larger than all seven continents combined.
The heavy, football field-size nets are dragged along the bottom of the ocean, often destroying corals and seamounts while capturing unwanted fish that will simply be thrown away.
"Close to 25 percent of all the fish in the world that are caught are discarded," according to Reichert, who said the United Nations is currently considering issuing a moratorium on deep-sea bottom trawling.
The National Fisheries Institute, which represents the seafood industry in the United States, sought to play down the impact of the report Thursday, saying it focused only on a worst-case, business-as-usual scenario.
"We're going to see natural fluctuations in fish populations," said Stacey Viera, spokesperson for the National Fisheries Institute. "As long as we continue the responsible management of fisheries, we're going to have fish now and into the future."
Experts say it's not only the amount of fish in the sea, and that the problem goes beyond the United States.
One billion people — many of the poorest people on the planet — rely on fish as their primary source of animal protein.
"The accelerating species loss threatens human well-being by undermining the ocean's ability to provide food, maintain water quality and recover from overfishing," Worm said.
Marine biodiversity is also threatened, said the study, with increasing shoreline erosion due to a variety of factors, among them the accelerating loss of the world's coral reefs.
Coastal mangroves that filter pollution runoff from land might also be affected if they lose the protection of those reefs.
Loss of mangroves could affect the quality of coastal waters, potentially driving away tourist dollars, Reichert said.
The study authors point out that fish populations have shown they can begin to bounce back in fisheries that have been closed or given greater protections.
"Unless we change the way we fish and reduce the amount [we catch], we simply will not solve this crisis," said Reichert.