Kerry Sheridan Yahoo News 18 Feb 11;
WASHINGTON (AFP) – Fewer big, predatory fish are swimming in the world's oceans because of overfishing by humans, leaving smaller fish to thrive and double in force over the past 100 years, scientists said Friday.
Big fish such as cod, tuna, and groupers have declined worldwide by two-thirds while the number of anchovies, sardines and capelin has surged in their absence, said University of British Columbia researchers.
Meanwhile, people around the world are fishing harder and coming up with the same or fewer numbers in their catch, indicating that humans may have maxed out the ocean's capacity to provide us with food.
"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 presented the research findings at the American Association for the Advancement of Science annual conference in Washington.
"By removing the large, predatory species from the ocean, small forage fish have been left to thrive."
The researchers also found that more than half (54 percent) of the decline in the predatory fish population has taken place over the last 40 years.
Christensen and his team examined more than 200 global marine ecosystem models and extracted more than 68,000 estimates of fish biomass from 1880 to 2007 for the study.
They did not use catch numbers reported by governments or fishing operators.
"It is a very different ocean that we see out there," said Christensen. "We are moving from wild oceans into a system that is much more like an aquaculture farm."
While the number of small fish is on the rise, the little swimmers are also being increasingly sought after for use as fishmeal in human-run fisheries, Christensen said.
"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," he said.
The researchers said that despite the spike in small fish, the overall supply of fish is not increasing to meet human demand.
"Humans have always fished. Even our ancestors have fished. We are just much much better at it now," said UBC scientist Reg Watson.
Examining the 2006 numbers, 76 million tons of commercial seafood were reported, meaning about "seven trillion individuals were killed and consumed by us or our livestock," said Watson.
Watson said fishing efforts have been growing over the past several decades, reaching a collective point of 1.7 billion watts, or 22.6 million horsepower, worldwide that year.
In terms of energy use, that would amount to 90 miles (150 kilometers) of "Corvettes bumper to bumper with their engines revving," he said.
"It looks like we are fishing harder for the same or less result and this has to tell us something about the oceans' health. We may in fact have hit peak fish at the same time we are hitting peak oil."
Seafood makes up a large part of the global human diet according to research fellow Siwa Msangi of the International Food Policy Research Institute, who said the rise in demand is largely being driven by China.
"Meat provides about 20 percent of the per capita calorie intake and of that... fish is about 12 percent," he said, referring to global figures.
Almost 50 percent of the increase in the world's fish consumption for food comes from Eastern Asia, and "42 percent of that increase is coming from China itself," he said.
"China is a driver of both the demand and the supply side. That is really why the management issue becomes so important."
Jacqueline Alder from the United Nations Environment program suggested that the world needs to see a swift cut in the amount of fishing boats and fishing days in order to allow global fish stocks time to gain numbers.
"If we can do this immediately we will see a decline in fish catches. However, that will give an opportunity for the fish stocks to rebuild and expand their populations," she said.
Projections about future fish populations decline further, however, when coupled with forecasts about the impact of climate change.
"Our study indicates indeed we may get a double whammy from climate change," said Christensen. "In the sense that higher water temperatures... are going to mean there will be less fish in the ocean."
Eat more anchovies, herring and sardines to save the ocean's fish stocks
We should consume less of the fish at the top of the food chain and more of their prey to rebalance the marine ecosystem, says fisheries scientist
Alok Jha guardian.co.uk 18 Feb 11;
Cut back on tuna and salmon and load your plate instead with herring and sardines if you want to help save the world's fish. So says the scientist who led the most comprehensive analysis ever carried out of fish stocks in the world's oceans and how they have changed over the past century.
The study by Villy Christensen of the University of British Columbia's Fisheries Centre confirmed some previous indications that populations of predator fish at the top of the food chain, such as cod, tuna and groupers, have suffered huge declines, shrinking by around two-thirds in the past 100 years. More than half that decline occurred in the past 40 years.
Christensen found that the total stock of "forage fish", such as sardines, anchovy and capelin, has more than doubled over the past century. These are fish that are normally eaten by the top predators. "You remove the predator, you get more prey fish," said Christensen. "That has not been demonstrated before because people don't measure the number, they don't go out and count them."
His call for consumers to shift their attention down the marine food chain from predators like tuna and cod to more unusual fish echoes that by celebrity chef Jamie Oliver, who suggests we should eat more coley, mackerel, dab, pouting, herring and sardines.
"I know you like your fish suppers, but our appetite for the same fish, day in, day out, is sucking the seas dry," Oliver has said. "I wouldn't bother waiting for the politicians to sort this one out, guys, you can really help from the comfort of your own kitchen ... Lay off the cod, haddock and tuna, diversify and cook up a wider range of fish."
Christensen presented his findings on Friday at the annual meeting of the American Association for the Advancement of Science (AAAS) in Washington, DC.
"Overfishing has absolutely had a 'when cats are away, the mice will play' effect on our oceans," said Christensen. "By removing the large, predatory species from the ocean, small forage fish have been left to thrive."
Christensen urged consumers to eat more of the burgeoning population of forager fish such as sardines and anchovies, while reducing their intake of top predators, in order to re-balance the world's fish species.
Today, the vast majority of forage fish that are being caught are used inefficiently in fish farms to feed salmon, for example. "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.
The rise in wild forage fish populations has knock-on effects on marine ecosystems. These fish eat more of the zooplankton in the oceans, which means that the next stage down the food chain – the plant plankton normally consumed by the zooplankton – blooms. "You get into a situation where you get a green soup, you get anaerobic conditions [low oxygen levels]. There are clear examples in the Black Sea," said Christensen.
In their analysis, Christensen's team collated data from more than 200 models of marine ecosystems around the world, using a technique called Ecopath, to estimate the mass of various fish in the world's oceans and how it has changed from 1880 to 2007.
Predators in general are an important component in food chains, said Christensen, preventing the spread of disease, for example. "In England some years ago, there was a crisis where they had killed a lot of the predators such as eagles. You had rabbits that got problems with diseases, there was massive die-off, the sick ones were not being eaten by the predators. We see less stable ecosystems if we do not have predators there."
The precipitous drop in top predator fish was also linked, in a separate study presented at the AAAS, to the rise in global fishing capacity. This has increased by 54% from 1950 to 2010 with no sign of a decrease in recent years.
"We need to cut back fishing efforts," said Christensen. "Society needs to decide what we want with the ocean – do we want to turn it into a farm? Or do we want to have something that is more of a natural ecosystem?"
Fishing Down Food Web Leaves Fewer Big Fish, More Small Fish in Past Century
ScienceDaily 18 Feb 11;
Predatory fish such as 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, according to University of British Columbia researchers.
Led by Prof. Villy Christensen of UBC's Fisheries Centre, a team of scientists used more than 200 marine ecosystem models from around the world and extracted more than 68,000 estimates of fish biomass from 1880 to 2007. They presented the findings at the American Association for the Advancement of Science (AAAS) Annual Meeting in Washington, DC.
Their finding of the simultaneous decline of predatory fish and increase of forage fish 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 Christensen, a professor in the UBC Fisheries Centre. "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!"
Christensen's presentation was part of an experts' panel to answer the question "2050: Will there be fish in the ocean?" The panel predicted that while there would be fish in 2050, it would consist mostly of the smaller variety.
