When scientists slap an acoustic tag on a fish, they may be inadvertently helping seals find their next meal. The tags, rods a few centimeters long that give off a ping that can be detected from up to a kilometer away, are often used to follow fish for studies on their migration, hunting, or survival rates. Researchers working with 10 gray seals (Halichoerus grypus) who were captive for a year have now reported that the animals—including the female seal pictured above, named Janice—can learn to associate the pings with food. The researchers let seals swim in a pool with 20 large metal enclosures containing, behind a flap, either a bucket of tagged fish, untagged fish, or nothing. After only a few days, the seals began to visit the pinging boxes more frequently than the other boxes. Even when all the boxes were empty—so not releasing any scents of food—the seals were more than twice as likely to swim to boxes that contained tags, the team reports online today in the Proceedings of the Royal Society B. If the findings hold true in the wild, the authors warn, they could skew the results of studies trying to analyze fish survival rates or predation.