In an analysis of scientific and historical data, researchers found that marine biodiversity - the variety of ocean fish, shellfish, birds, plants and micro-organisms - has declined dramatically, with 29 per cent of species already at high risk.


By extending this pattern into the future, the scientists calculated that by 2048 all species would be in collapse, which the researchers defined as having catches decline 90 per cent from the maximum catch.


This applies to all species, from mussels and clams to tuna and swordfish, while ocean mammals such as whales and dolphins will also be affected, said Boris Worm, lead author of the study published in Science journal on Thursday.


"Whether we looked at tide pools or studies over the entire world's ocean, we saw the same picture emerging," Worm said in a statement.


"In losing species we lose the productivity and stability of entire ecosystems. I was shocked and disturbed by how consistent these trends are - beyond anything we suspected."


Call for action


Worm and an international team spent four years analysing 32 controlled experiments and other studies from 48 marine protected areas and examined global catch data from the United Nations Food and Agriculture Organisation's database of all fish and invertebrates worldwide from 1950 to 2003.


The scientists also looked at a 1,000-year time series for 12 coastal regions, drawing on data from archives, fishery records, sediment cores and archaeological data.


The researchers called for new marine reserves, better management to prevent overfishing and tighter controls on pollution.


In the 48 areas worldwide that have been protected to improve marine biodiversity, they found that "diversity of species recovered dramatically, and with it the ecosystem's productivity and stability".


However, the National Fisheries Institute, a trade association for the seafood industry, said that fish stocks naturally fluctuated in population, the institute said in a statement.


It also said it was working on new technologies "that capture target species more efficiently and result in less impact on other species or the environment", which it said would help ensure that ecosystems or native species were not damaged.