Porpoises plan their dives and can set their heart rate to match

Two captive harbour porpoises called Freja and Sif have helped to reveal that porpoises --and probably all cetaceans -- consciously adjust their heart rate to suit the length of a planned dive. By doing this, the animals optimise the rate at which they consume oxygen beforehand to match the intended depth and length of their dive. "Until now, we knew that the heart rates of porpoises and cetaceans in general correlate with different dive factors, such as dive duration, depth and exercise," says Siri Elmegaard of Aarhus University in Denmark, who led the research. "Now we can conclude that harbour porpoises have cognitive control of their heart rate." The discovery might also provide another explanation for how exposure to loud noise from shipping, sonar or subsea exploration harms cetaceans and possibly triggers strandings.