A blue shark captured by the underwater camera network. The targets: loggerhead turtles, silky sharks and sailfish. The mission: figure out how many of them are left. The UK announced on Saturday it would launch a worldwide effort to monitor wildlife in the open oceans, hoping to fill a blue hole of scientific knowledge and get a clearer sense of which aquatic populations are under threat. The project, akin to an underwater spy network, will fund a fleet of small action cameras, complete with bait, to be deployed about 30 feet beneath the ocean’s surface. Researchers will place a camera in the water where they hope to gather data, and it will record anything that swims near within a given window of time. The plan is for the project to span the globe, covering four oceans and the Caribbean in waters near 10 of the UK’s overseas territories.