Thousands upon thousands of whales and dolphins are killed every year by fishing nets because the strands of the nets are invisible to their sonar. Take that, evolution! But seriously, it’s a major problem and various things have been tried to alleviate the damage. The latest idea is to use these basketball-sized acoustic reflectors, which as you might guess reflect sonar signals very well and would appear quite “bright” to the poor aquatic mammals.
They were originally used to mark mined areas so ships wouldn’t blunder into them, but they don’t look too expensive so I guess they figured they could use them to save the whales. They also have no complicated electronics and require no power, so they’re easy to maintain. Double grog ration for the guy who came up with these things.
Military beacons to aid sea life [BBC News]