Harbor porpoises, Phocoena phocoena, live life in the fast lane. Compared to other toothed whales, they mature earlier, reproduce more frequently, and have a shorter lifespan. They also require a lot of energy just to survive. According to new findings published in Current Biology this week, these marine mammals are constantly hunting and eating, day and night. They hunt up to 550 fish an hour with a 90 percent success rate.
Being the smallest cetacean living in the cold temperate waters of the Northern Hemisphere, harbor porpoises lose a lot of heat and can only store a limited amount of energy. That means they probably have to eat a lot throughout the year to support their metabolic requirements.
To study harbor porpoise foraging behavior, a team led by Danuta Wisniewska of Aarhus University attached high-resolution data loggers to five wild porpoises using suction cups (pictured below). These tags recorded both movement and sound. "This is the first time we have been able to measure simultaneously how a marine mammal hunts and how often it is successful," Wisniewska said in a statement. "The trick here was to tap into the echolocation sounds that porpoises use to sense their environment. Porpoises make hundreds of clicks a second as they approach prey, and the echoes coming back give us incredible detail about what the prey are doing."
Turns out, the porpoises hunt small prey between 3 and 10 centimeters (1.2 to 4 inches) long nearly continuously. They’ll try to catch as many as 550 fish an hour. The researchers describe these foraging rates of nearly 10 fish a minute as "ultra high." And with a success rate of over 90 percent, harbor porpoises are one of the planet’s most success hunters. You can watch them hunt here and here.
But they live on a knife-edge. Requiring so much energy just to survive means they must eat all the time or else they’ll starve. While they do target fish that are smaller than those of interest to commercial fisheries, "relying on such small prey makes porpoises especially vulnerable to disturbances, because there is no room for compensation," Wisniewska added. Even a moderate level of disruption in the busy shallow waters that they share with humans could impact the porpoises severely.
Monika Dyndo_Fjord & Belt
