 |
Scientific Name: Phocoena phocoena
Category: Cetaceans
What are Harbor Porpoises and What Do They Look Like?
There are many aquatic mammals that live in the ocean. Two important groups are porpoises and dolphins. You may have trouble telling them apart. Do not feel badly, people often confuse them. Dolphin bodies are longer and sleeker; porpoises are shorter and chubbier. The dorsal (top) fin of the dolphin is shaped like a curling ocean wave. The porpoise dorsal fin is shaped like a triangle and sometimes porpoises are mistaken for sharks. Scientists can easily tell them apart by their teeth. Porpoises have cone-shaped teeth, while dolphins have spade-shaped ones. However, it is unlikely you would be able to ask them to open wide, like at the dentist, to examine their teeth. So we need other ways to tell them apart. Dolphins are often seen jumping and swimming in the wakes of boats, while porpoises are shy and come to the surface just to breath. If you can hear sounds or clicks from the mammal, it is a dolphin. Porpoise sounds are inaudible to the human ear. There are six species of porpoises and the most well-known in the northern hemisphere is the harbor porpoise.
The harbor porpoise is the smallest of the porpoises and grows to only 1.4 m to 1.9 m (4.6-6.2 feet) in length. Its average weight is 61kg (134 pounds). Females are usually a little larger than males. Porpoises are usually dark on the top side (dorsal) and lighter in color on the bottom and there is a black stripe that runs from the edge of the mouth or eye to the flipper on either side of the body. The snout is short and blunt. They live in coastal areas of the northern hemisphere where the water temperature is about 15 °C (59 °F). Sometimes they swim hundreds of miles up rivers. The harbor porpoise can live up to 20-25 years.
Where Do Harbor Porpoises Live and Breed and What Do They Eat?
The porpoises live individually or in small groups of 6-10, although groups of 50 have been reported. Harbor porpoises are usually 3-4 years old before they breed. Mating season is June to September and 11 months later a baby calf is born. The calf usually nurses for 8 months. As baby porpoises grow, they need to eat 8% of their body weight each day. Since the harbor porpoise is a mammal, it must live near the surface and it rises about every 25 seconds to breath. When diving for food, they can stay down for 4 minutes.
The harbor porpoises eat squid and non-spiny fish, like capelin, herring, whiting, cod, squid, pollock, sardines, and sprat. They must eat 10% of their body weight every day. White sharks and orcas are their enemies. Scientists have found that some bottlenose dolphins will kill harbor porpoises, but not eat them. This reduces the bottlenose dolphins competition for food, because they both eat the same fish.
What Are Some Threats To The Harbor Porpoise Population?
The harbor porpoise is not endangered and the global population numbers in the hundreds of thousands. They frequently are caught in fishnets even though their 'echolocation' is strong enough to detect the nets, they still are trapped. Echolocation is the use of sound to locate objects and the porpoises use this to find schools of fish. Danish fishermen used to hunt them for food and to get fat to burn in lamps, similar to the way whale blubber was used in other places. In addition to the fishnet hazard, harbor porpoises suffer from chemical and noise pollution.
Research Links Related to Harbor Porpoise:
|
 |
