Porpoises are often mistaken for dolphins, but they are a group of fully aquatic mammals that have a striking resemblance to a dolphin.
Both porpoises and dolphins are classified under the family known as Phocoenidae, parvorder Odontoceti (toothed whales).
However, porpoises are closer related to belugas and narwhals than the actual dolphins.
Scientific classification
- Kingdom: Animalia
- Phylum: Chordata
- Class: Mammalia
- Order: Artiodactyla
- Infraorder: Cetacea
- Superfamily: Delphinoidea
- Family: Phocoenidae
Porpoises are one of the large mammals of the sea. During the Middle Ages, these animals were called ‘sea pigs’ or mereswines.
In those days, people consumed them a lot. There was a substantial population of porpoise residing along the Dutch coast. Those were the times when creatures like anchovies and other little fatty fish were in abundance.
The porpoises were known to follow the fish into harbors, ant they earned them the title of harbor porpoises. Porpoises became scarcer halfway into the 20th century, however, there has been a tremendous increase in the number of sightings since 1995.
The porpoise is now the easiest to spot cetaceans in the North Sea.
Spotting porpoises
It is not exactly easy to see porpoises at sea. Unlike other kinds of dolphins, porpoises hardly ever jump out of the water randomly.
You’re not likely to sight more than the upper part of a porpoise’s back with its dorsal fin when coming up for a breath of fresh air. Porpoises either live alone or in groups made up of three to five animals or even more.
If you see two animals together, there is a high chance that they are mother and calf. These mammals sometimes form large groups when they migrate.
From a boat or from land, the most likely time to notice a porpoise is during the winter.
Distribution of porpoises
The porpoise naturally live in all shallow and relatively cold coastal seas. There are about 250,000 porpoises that live in the entire North Sea, of which there are tens of thousands in the Dutch waters.
When there were a ton of anchovies around, porpoises were also in surplus in the Zuiderzee and the Wadden Sea. These days, they are a rarity.
Porpoise diet
Porpoises are voracious eaters, and they find their food underwater with the aid of sonar. The porpoises that live in the coastal region of the Netherlands and also those in the Baltic Sea are known to eat mostly small benthic fish like guppies.
Porpoises in the open North Sea primarily feed on herring, mackerel, and sprat. Porpoises that live in the German Wadden Sea mainly eat small flatfish.
The large flatfish are known to be dangerous for porpoises. A good percentage of porpoises that have been washed ashore were discovered to have choked to death after feeding on large flatfish.
Two decades ago, the porpoises living in the North Sea fed mainly on whiting. However, this specie of fish is not that common anymore. That is why porpoises have switched to gobies.
Gobies are a much smaller kind of fish than whiting, so they need to eat much more of those to satisfy their needs. Some scientists have discovered that porpoises that get stranded in the summer seem to have issues finding enough food.
Porpoises feed on around five kilograms of fish every day– this is approximately 10% of their body weight. There is also a theory that suggests that porpoises help each other to search for food using their sonar system.
You can imagine how easy it is to find food in the sea when the porpoise group is spread out.
Mating season for porpoises
Porpoises are known to mate from the period of June to the early parts of August. Porpoise calves are birthed 11 months later so that July becomes the birthing peak.
Females become sexually mature once they are between the ages of 5 to 6. Most porpoise females do not bear calves every year. Calves are usually nursed for about 8 months, after which they adopt a fish diet.
That is not always the easiest process: many young porpoises typically have trouble finding the right amount of food to eat. Most of the porpoises found stranded along the beach are often not much older than one year.
At the age of one, porpoises are around 100 centimeters in length.
Porpoise calves
Porpoise calves are nursed for about eight months, although they will have to try a fish during that period. This time is vital for the calf to learn all the tricks of the sailing trade from its mother.
In September 2011, workers on a gas production platform noticed these lessons. The mother remained with her calf for a couple of weeks under the platform.
During this time, the workers noticed how the calf was nursed regularly and how the mother brought fish to the surface from time to time, which she would then release close to the fast-approaching young.
The calf will then attempt to catch the little fish. Sometimes it was a successful event, but that isn’t the case always.
After the nursing period is complete, the calf will have to switch to a diet of fish. That is not always an easy process as many young porpoises have been noticed to often have trouble getting enough food to eat.
Fast facts about porpoises
Porpoise size: maximum of 190 centimeters (between 70-80 centimeters at birth)
Porpoise weight: Maximum of up to 60 kilograms (around 5 kilograms at birth)
Porpoise color: The back is usually dark gray, light grey sides with some dark spots, white belly, and a chin
Life expectancy: 12 to 15 years
Porpoise food: fish, such as mackerel, herring, gobies, sprat, whiting, and cod; cuttlefish, worms, crabs, and snails
movement:
dive: 4-6 minutes all the way down to 200 meters deep
speed: max of 23 kilometers per hour
Porpoise enemies:
man: loss of habitat, tangled in nets, acoustic noise, and pollution.
animals: dolphins, grey seals, and killer whales
Porpoise reproduction:
maturity: between 3-6 years old
frequency: once birth every 1-2 years with one calf
pregnancy: between 10-11 months
nursing: between 7-8 months
