Marine researchers estimate there are two billion tonnes of fish in the oceans, the equivalent of about 300 kilograms for every human on the earth.

The problem is about half of that biomass consists of smaller fish found in the mesopelagic zone, extending in the oceans to a depth of about 1,000 metres, and not commercially fished.

“Small open-ocean fish,” said Villy Christensen, an ecosystem modeller with the University of B.C. Fisheries Centre. “Nice for whales to eat.”

And among those species that measure at least 90 centimetres and are commercially fished, biomass has declined by about 55 per cent over 40 years.

“There’s been a drastic composition change,” said Christensen. “This is global, this is for everywhere.” Speaking at the annual meeting of the American Association for the Advancement of Science, continuing at the Vancouver Convention Centre through today, Christensen called for more research on predicting the effect of climate change on oceans to better manage fisheries and stocks.

Scientists say warming of the oceans under climate change will push more fish species northward in search of the cooler waters – a potential benefit to nations in northern latitudes.

However, William Cheung, an assistant professor in the Fisheries Centre, cautioned any such benefit could be offset by the fact that warmer waters hold less oxygen for fish to utilize.

Increased acidification of the oceans under climate change will also compromise marine productivity at the base of the food chain.

All will have the effect of reducing potential commercial catches in future years, Cheung concluded.

The Vancouver Sun