Narrator: This is Science Today. Researchers at the University of California , San Diego 's Scripps Institution of Oceanography are leading a consortium that studies sharks and rays off Southern California . Marine biologist Jeffrey Graham says the main objective is to raise awareness about the natural history and ecology of many of the sharks and rays – populations that have been declining partially due to fishing and the effects of humans on inland water bodies.

Graham: With this has come a general decrease in the population size of most of the sharks and most of the rays in the local area. They can be seen, many of them, but their numbers are less abundant than they were and this means that there are ecological and biological changes occurring in these habitats.

Narrator: Graham's lab recently completed tagging adult thresher sharks with acoustic and archival monitoring tags.

Graham: That merely ride with the shark for a long period of time and then when the shark is caught by a commercial or recreational fisherman, it's brought ashore, given back to us and we can download the data about where that shark went during the time it was at sea.

Narrator: For Science Today, I'm Larissa Branin.