Bigger Fish Suffer More from Climate Change

Have you noticed there are fewer big fish than there used to be? Overfishing and killing off all the larger members of a species are leaving a gene pool of fish unable to grow so large. And fishing is getting easier because the warming climate is depleting oxygen in the ocean, driving fish toward the surface, where they are easier to catch.

A report by the BBC's environment correspondent, Matt McGrath, tells how that is the conclusion of the biggest study of its kind, undertaken by the conservation group IUCN.

Warming oceans are less able to hold dissolved oxygen. As many as 700 ocean sites are now suffering low oxygen levels compared with just 45 in the 1960s, and researchers say the depletion is threatening species including tuna, marlin, and sharks. They estimate that between 1960 and 2010, the amount of oxygen dissolved in the oceans has declined by an average of two percent, but in some tropical locations, the loss can be as much as 40 percent. Waters with less oxygen favor species such as jellyfish, but they're not good for bigger, fast-swimming species like tuna, which have greater energy needs. Seeking more oxygen, they are moving to the shallow surface layers of the ocean, where there is more oxygen, making them more vulnerable to over-fishing.