Locate Long Island Sound on this map. Consider seasonal air and water temperatures in each of the ranges. [Note: “stranding” refers to when a seal is found in distress on a beach and is unable to return to the water.] The seals in Fishers Island Sound divide their time between rocky ‘haul-out’ locations and the water, so the number of seals observed by Project Oceanology students may be influenced by both air and water temperature.

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Seals have many physical and behavioral adaptations for maintaining their internal temperature, a process known as thermoregulation. A harbor seal’s core temperature is about 37.8℃ (100℉), which means that they are constantly losing heat to the cold water that surrounds them.  Seals combat this heat loss in several ways.  First, their metabolic rate is somewhat higher than land mammals of the same size. This high metabolism helps them generate body heat for warmth.  Second, their bodies are insulated by thick layers of blubber (up to 30% of their body mass!) and also (to a small extent) by their fur.  Third, while they are in the water, blood vessels in their skin contract, shunting blood inward to the core of the body and reducing heat loss at the surface.  Finally, seals can warm up by ‘hauling’ out on the rocks.  While they are on the rocks, the skin blood vessels dilate, allowing greater heat exchange between the seal and the environment.  

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The image below shows thermal images of the surface temperature of a seal pup that has been basking in the sun (left), and the same seal pup after a 20 minute swim in cold water.