Harbor seal

Since 1988, I have been observing a population of Harbor seals that use a haul out rock near my home in Downeast Maine. Recently I was asked by a biologist why seals "porpoise" like this and didn't have a single answer. There seem to be many purposes to porpoise... to see where they are going in relation to landmarks, to impress when they arrive at a haul out site (rocks where seals are resting, that was the case in this photo), to keep track of each other*, to herd and startle fish, for the shear joy of it!

* often when the seals leave the haul out as a group they will all porpoise though not in sync