Even though many, at first sight, would prefer sardines on the table to sharks in the water, the decline of predator fish in the oceans has led to an excess of smaller species that seriously threatens the ecological balance, scientists say.
A new study, presented recently at the American Association for the Advancement of Science (AAAS) Annual Meeting in Washington, DC, claimed that predatory fish such as sharks, cod, tuna, and groupers have declined by two-thirds over the past 100 years, while small forage fish such as sardine, anchovy and capelin have more than doubled over the same period.
The findings in the study by a group of scientists at the University of British Columbia in Vancouver provides the strongest evidence to date that humans are indeed “fishing down the food web” and impacting ecosystems globally. The UBC team also found that of the decline in predatory fish population, 54 per cent took place in the last 40 years alone.
“Overfishing has absolutely had a ‘when cats are away, the mice will play’ effect on our oceans,” said Villy Christensen, a professor in the UBC Fisheries Centre, who led the group. “By removing the large, predatory species from the ocean, small forage fish have been left to thrive.”
While the doubling of forage fish amounts to more fish production, Christensen cautioned that the lower trophic-level food web is more vulnerable to environmental fluctuations.
“Currently, forage fish are turned into fishmeal and fish oil and used as feeds for the aquaculture industry, which is in turn becoming increasingly reliant on this feed source,” said Christensen. “If the fishing-down-the-food-web trend continues, our oceans may one day become a ‘farm’ to produce feeds for the aquaculture industry. Goodbye, wild ocean!”
Another serious consequence further down the food chain, according to the scientists, would be the risk of algae blooms, where populations of simple algae get out of control and choke the oceans; this because the forage fish deplete the zooplankton that would feed on the algae.