Ocean dead zones could cut tuna numbers

By Australian Broadcasting Company, (ABC News)
Fri Dec 3, 2010

Southern bluefin tuna swim in the open ocean
The increasing prevalence of dead zones may have an impact
on southern bluefin tuna stocks (AAP: Kerstin Fritsches, file photo)

The zones are so low in oxygen that fish and other sea life cannot survive in them.

Associate Professor Mark McCormick from James Cook University says the tuna pass through some of the zones during their annual migration.

He says while there is no immediate cause for alarm, the increasing prevalence of dead zones may have an impact.

"Sometimes they actually shoot through there to feed on things and they can’t stay very long in there because there’s not very much oxygen," he said.

"If they stay really too long they’re going to die.

"If they spend a moderate amount of time it might actually end up reducing their growth rate if they do it too often."