Predator fish in oceans on alarming decline, experts say

A worker in the southern Philippine city of General Santos unloads yellow fin tuna; the city is considered the tuna capital of the Philippines, with exports to the United States and Europe. (AFP/Getty Images)

In an effort to stabilize some fish populations, national and international organizations and governments have placed quotas on the yearly catches of some species, and have banned the taking of endangered fish entirely in some areas. Some regulations have also been placed on the kind of netting and trawling that can be used in sensitive areas.

But the fishing fleets are growing in size and sophistication, said University of Tasmania scientist Reg Watson. "Humans have always fished," he said. "We are just much much better at it now."

Examining 2006 catch results, his team found that 76 million tons of commercial seafood were hauled in - which he said equates to 7 trillion individual fish.

Watson said fishing activity has been growing quickly over the past several decades, with increasingly more energy and effort exerted to bring in equal or smaller catches. Nations also are paying substantial subsidies to their fishermen, he said, especially in East Asia.

"It looks like we are fishing harder for the same or less result and this has to tell us something about the oceans' health," he said. "We may in fact have hit peak fish at the same time we are hitting peak oil."

Yet demand is growing fast, again most dramatically in East Asia. According to International Food Policy Research Institute research fellow Siwa Msangi, the rise in demand is largely being driven by China. 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," Msangi said. "Projections about future fish populations decline further, however, when coupled with forecasts about the impact of climate change," which is expected to warm the oceans considerably.

"Our study indicates indeed we may get a double whammy from climate change," said Christensen. "Higher water temperatures are going to mean fewer fish in the ocean and less plant life for them. This will be especially true in the tropical areas."

Oceans, he said, are increasingly being treated like farms, but the effort cannot be successful on a large scale. Intensive farming on land requires antibiotic treatments and pesticides to make up for the loss of a balanced ecosystem. In aquaculture, the same is true, and raising salmon or tilapia also requires importing tons of fish meal and fish oil from smaller species.

Christensen gave an example of the kind of dynamics he expects to see more and more in the oceans. Some years ago, a huge sardine fishery off Namibia in southern Africa crashed because of overfishing and a related drop in oxygen in the waters. When the sardines are depleted, he said, generally anchovies move in. Both can be consumed, but sardines bring a much higher price and so are preferred.

With so many anchovies and so few sardines, fishing fleets decided to work toward greatly reducing the anchovy population in the expectation that the sardines would come back. But instead of sardines, the fish that moved into the niche was the bearded goby - which is inedible for humans and eats up the ocean food that might one day again have supported sardines or anchovies.

"Nobody," Christensen said, "can control the ocean."