What's in Your Watershed?
The Playful Harbor Porpoise
They're back! After a 65-year hiatus, the 'little cows' of the ocean have returned to the San Francisco Bay. Why did they leave in the first place? While their disappearance is unclear, environmental conditions along with the Bay becoming a major military hub at beginning of World War II are likely candidates. All we can say for certain is that since the Clean Water Act in 1972 and improved sewage treatment, they have returned. Extensive research is planned over the next five years to study their re-emergence.
Who are these critters?
The harbor porpoise (Phocoena phocoena) is one the smallest of the marine mammals and is the smallest of the six types of porpoises. At birth they are as small as two feet in length with a weight range of 6.5-10kg. They have a life span of approximately 15 years.
Harbor porpoises are like Hershey kisses bobbing on the Bay. Their backs are dark grey and you can see them popping out of the water as they swim along the surface. Their sides are a lighter grey and speckled, and their bellies are white with small grey stripes. Unlike their dolphin relatives, harbor porpoises have a rounded, blunt head and a pronounced forehead.
These porpoise are found in northern and subarctic waters specifically in bays, estuaries, and harbors-- hence the name. They prefer to be in waters that are cooler than 60 degrees Fahrenheit. They are shy animals and avoid loud vessels. They travel and forage alone but will pair up or be in small groups of 6 to 10.
The harbor porpoise diet consists of small pelagic schooling fish such as herring, anchovies, smelt, and sprat. They will eat squid and crustaceans. They either forage on the ocean floor (less than 200 meters) or near the surface when they are going after sprat. They eat a lot--consuming 10% of their body weight each day.
Their main predators are the white sharks and killer whales. Environmental threats to the porpoise are heavy metals, PCB, and pesticides that will be absorbed into their fat. The animal can carry these toxins in their bodies and until they are forced to use their fat reserves at which point they become poisoned.
These creatures have an amazing ability to echolocate. They create sounds waves which are reflected and then are interpreted to either communicate or locate prey along with navigating through murky waters.
Where can I see them?
The porpoises can be seen from the walkway on Golden Gate Bridge or the shores of Cavallo Point at Fort Baker. A special permit is required to approach these protected animals in the water. There have also been sightings at north end of Angel Island. The best time to catch these playful porpoises is two to four hours after high tide.