Wait, “shiver me seals?” What’s that supposed to mean? We’ve had some questions from visitors lately about our northern fur seals “shivering.” Rest assured, it is not because they are cold…the Bering Sea, where northern fur seals live in the wild, is a much chillier place than Seattle!
Some colleagues at the Long Marine Laboratory in Santa Cruz, California have done extensive work on thermoregulation in marine mammals and explained that pinnipeds (fin-footed mammals) don't need to shiver for the same reasons that most land animals shiver. When a human or other land animal is exposed to cold temperatures and their core body temperature drops too low, one of the physiological responses is muscle shivering to produce heat. Pinnipeds can regulate their core body temperature by dilating or constricting the blood flow to their extremities (this works sort of like a car radiator). They can live in extremely cold temperatures and still keep their core body temperature warm.
So why do we see pinnipeds shivering when the air temperature isn't even as cool as the water temperature? This shivering is a surface skin response to evaporative cooling. We most often see our animals shiver when they are hauled out resting on land or are resting fairly quietly at the surface of the water. In both these instances, the water on their skin and fur is exposed to air and is evaporating, which is cooling the surface of their body enough to make them temporarily shiver. This is not unlike us going for a run on a warm day and perspiring but when we stop running we might get goose bumps or even begin to shiver even though our bodies are still very warm from running! All we need to do is towel off the water and we stop shivering. Once the seals completely dry off, they stop shivering too.
Come visit our northern fur seals Al, Commander and Woodstock at the Aquarium!