In the 19th century, many people, including the naturalist Thomas Huxley, thought there was an endless supply of fish in the sea. But nowadays some fisheries are collapsing. Learn more about no-fishing zones -- today on Earth and Sky.

JB: This is Earth and Sky. Callum Roberts is a marine conservation biologist at the University of York in England. He spoke with us about marine reserves -- places that are closed to all forms of fishing.

Callum Roberts: What we're finding with marine reserves is that they are very effective tools for rebuilding fish stocks. When you establish an area that's off limits to fishing, then the fish live longer, they grow larger, and large fish produce many, many times more eggs than small fish do.

JB: And as fish stocks build up inside reserves, fish will migrate from the more crowded protected area and spill over into nearby fishing grounds.

Callum Roberts: What's exciting about marine reserves is that they are able to perform a dual role. They can protect coral or other kinds of marine life inside the reserve. They can protect the fish inside the reserve. They offer a refuge from fishing for things that are very vulnerable to being impacted by the fishing process, such as some of the sensitive marine life that lives on the sea bed and can be damaged by trawling, just as an example. And at the same time though, they can support an extractive industry, the fishing industry. And they can do this because the fishing industry benefits in surrounding areas.

JB: Thanks today to the U.S. Forest Service and to the National Fish and Wildlife Foundation -- supporting the conservation of native fish, wildlife, plants and their habitats. I'm Joel Block, for Earth and Sky.