I was on a seal-watching trip recently, and I was lucky to see some pups feeding. I thought I would take some notes as it was fascinating and decided to write this post.
Seals have inverted nipples. When the pup is ready to feed, they nose at the area to release the nipples. Once they have latched onto it using their indented tongue, they will suck the milk, going between the nipples in turn.
In order for seals to put on the layers of fat that they need to survive, they need to learn how to breastfeed, which they learn on their first day.
Seals feed while on land and not while in water as other aquatic mammals such as whales and dolphins do.
Do seals produce milk?
Seals are semi-aquatic mammals and possess the typical characteristics of mammals. Seals have mammary glands and produce milk to feed their young.
Do seals have nipples?
Seals are mammals and do have nipples to produce milk. Some species have two, while others have four, depending on the number of offspring they are likely to have.
How do seals feed?
Forming a bond between the mother and the pup is essential for the survival of the pups, and getting suckling going is required early on in their lives. Cubs will attempt to feed soon after birth, and most will feed within the first six hours.
The pup will not know where to suck to start, and the mother will move their body around to stop the pup from nosing at the wrong parts of her body. The duration of the lactation period in seals is short, so the cub and nipple have to link up quickly, and the mother and cub have to get into a routine early.
The female moves onto her side as the pup nuzzles her, trying to find the nipples. These are found towards the tail end of the belly. The nipples are turned inwards to stop them from getting aggravated or caught by rocks. However, they pop out once the seal tries to get to them.
The female may push the pup down to the correct part of her body to help them locate the right area. She will move them down using her flipper, using an up and down motion called flippering.
Once the pup finds the nipple, they will grab on with their mouth, using the indented tip of its tongue around the nipple. It will suck milk for a few minutes before changing to another nipple.
Once the pup moves between the mammary glands, the feeding stops. Suckling takes about ten minutes, with five or six feedings per day.
The pup doesn’t grow much on the first day, but once it learns to suck correctly, the flow of milk improves considerably. The growth rate is phenomenal once they know how to locate the nipples and feed properly.
How much milk do seals drink?
The milk is fat-rich and contains about 60% fat, giving it a creamy consistency. A pup will drink up to two and a half litres per day, although because it is so thick, it could also be said they are eating it.
What is the importance of milk to the young seals?
The weight of a grey seal can double in the first week, with a daily increase of almost 2kg (4 1/2lb.) The lactation period lasts up to eighteen days, and in this time, they will have tripled their weight at birth. After three weeks, they can weigh up to 45kg (100lb.)
Although their length doesn’t grow much in this time, the weight comes from the thick layers of fat called blubber that they put on. The blubber acts as a food store and as insulation in cold waters.
Other seals can feed for up to one month, such as harbour seals, which fatten up considerably in the first few weeks.
As the pup’s weight increases, the mother’s weight decreases. Grey seals don’t feed at all while feeding their young, although harbour seals stay with their cubs for the first few weeks before spending longer away to feed.
While they are fasting, the females use the fat they have stored to ensure their metabolic and activity needs are met. This is on top of the immense drain of producing milk.
Grey seals can lose up to 4kg (9lb) daily while caring for their young, using about 3,000 calories per day. Their weight drops down rapidly from 180kg (370lb) to just 95 kg(210lb) in two and a half weeks.
The females look unlike the rotund, chubby seals we are used to seeing, and you can even see the hip bones in some species.
What do seals eat after milk?
Once lactation has ended, the females become receptive again to males and will mate again. They will then leave the breeding group and their pups, leaving them to find food themselves. The female will be gone longer and more often, and the pups attempts to feed from them will be rejected.
Once the pups realise that there is no milk, they leave their birth sites and go their own way. Pups have to learn to fend for themselves and have to learn how to catch their prey.
They feed on small fish such as cod, flatfish, herring, salmon, octopus and squid. They will eat whatever is most abundant in the area, including shellfish and crustaceans if available.
Larger seals, such as grey seals, will eat about 5kg (11lb) per day, while harbour seals will feed on less due to their smaller size.
They will eat their prey in one gulp if small enough, however, for larger fish, they will hold them in the front flippers and tear chunks of them off with their teeth. They will also skin some fish if they don’t like the rough texture such as on lumpsuckers.