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Author: Marco Boshoven

Hooded seal

Geschreven door Marco Boshoven op . Gepost in Zeehondensoorten.

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Scientific name: Cystophora cristata
Family: Phocidae
Size: male 3.50 meters; female 2.00 meters
Weight: male: 400 kilo; female: 300 kilo
Habitat: Northwest Atlantic Ocean and the Arctic
Endangered status: vulnerable

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“A male hooded seal makes tries to attract females in an extraordinary way: they have an inflatable, stretchy, red cavity in their nose (also called hood).”

External features of the hooded seal

Hooded seals can reach a weight of about 145 to 352 kilograms and a length of 2 to 2.6 metres. Large animals can even reach more than 400 kilograms. Hooded seals have a large and broad but relatively short head with large nostrils. The head and flippers are usually coloured completely black. The rest of the body is white in both males and females with black spots of all sizes and shapes1,2. In contrast to their robust body, their flippers are relatively short.

Gender differences

Imagine this: you inflate a red balloon bigger than your head. You would stand out in an audience. So does a male hooded seal, but with a hood coming from their nose! This is where the species gets its name from. They do this to attract the attention of females, but also to threaten other males (and compete when mating with females)1,6.

In fact, males have a rather large nose, the skin of which they can inflate into a black "balloon". This one can be bigger than their own head! But that's not all, as they can additionally inflate a sheet on the inside of their nose into a red "balloon". They inflate these different air sacs to show how big they are. The nose of females has no other notable modifications and they remain somewhat smaller than males.

Distribution and status

Hooded seals are found in the North Atlantic and the Arctic Ocean. They are native to Canada, Greenland, Iceland and Norway. It is estimated that there are about 600,000 hooded seals in the North Atlantic and another 100,000 or so in the Arctic Ocean. The hooded can swim in water from -1.9°C to 10.7°C9. 

Did you know...

The habitat of the hooded seal is decreasing due to climate change?

Decreasing habitat

This gives? the hooded seal the "vulnerable" status on the IUCN Red List, meaning that the species may be endangered in the future2,3The habitat of the hooded seal, like other Arctic or ice dependent species, is threatened by habitat loss - due to climate change. Therefore, it could be the case that the hooded seal will be listed as an "endangered" species2. Because of its vulnerable status, the hooded seal is protected by the Marine Mammal Protection Act1.

Humans hunting hooded seals

In the past, there was intensive and unsustainable commercial hunting of hooded seal mothers for oil and leather or the pups' fur. Usually, when pups were hunted for their fur, the mothers were also killed because they would try to defend their pup. In Greenland today, people still hunt hooded seals for meat or fur1,2,5,8.

Further threats to the hooded seal population include entanglement or bycatch, competition for food with commercial fisheries or other predators, climate change and, as usual, typical diseases1,2.

Diet and foraging

The diet of hooded seals consists mainly of squid, starfish, mussels and some fish species such as Arctic and Atlantic cod and herring. Young hooded seals eat pelagic crustaceans, such as krill 

Did you know...

Hooded seals can dive as deep as 1 kilometre?

While foraging, hooded seals dive as deep as 100 to 600 metres. They then do so for about 13 to 15 minutes. However, it is known that they can even reach a depth of 1,000 metres! Hooded seals can stay underwater for 1 hour and can travel as fast as 27 kilometres per hour 1,2,7.

Behavior of the hooded seals

Hooded seals are solitary animals. That means they prefer to go their own way. In general, hooded seals show aggressive and territorial behaviour. Males are known to patrol along the ice edge and often stay close to females. There is considerable fighting between males, with often bloody results, whilst showing off vocally their inflated red 'hood'1,5. 

The only social contact with other hooded males occurs during the mating and moulting season 1,10. The males then appear together in small groups. But: even then they will avoid lying close together2.

Did you know...

Hooded seals can stay at sea for weeks without resting?

The hooded seal is a migratory species: they migrate. Sometimes they spend weeks at sea without resting. When they do rest, they prefer to do so on floating pack ice 6,8. Their annual migration cycle begins when they are sexually mature1. Males are sexually mature at 6 years of age, females at 3 to 6 years of age7. The molting period is annual in July, after the young are born 1,2. 

Voortplanting bij de klapmuts

From April to June, the hooded seals have only 2.5 weeks to mate6. Hooded seals are polygamous: males mate with several females. Mating takes place under water2,4.

Diapause and pregnancy

As with all seal species, there is a diapause after fertilization. A diapause means that there is a time between fertilization and the actual pregnancy, so implantation is delayed. This delayed implantation of the fertilized egg takes about 3 to 4 months. After these months, gestation lasts about 8 to 11 months7,8. 

Birth and nursing period

A hooded seal gives birth to one single pup. The pup is born and suckled on the sea ice1,2. The mother will aggressively defend her pup. Usually, the mother will not forage while lactating. Usually, a male will assist the mother and her pup and stay nearby. When the mother will suckle her pup, the male can mate with her directly in the water5,8. 

The birthing season usually takes place around March and April5. The pups are also known as "bluebacks" because their fur appears blue-grey. Unlike their backs, the pups have a whitish belly. The fur falls out during the molt when they are 14 months old1. 

Did you know...

Pups of hooded seals have the shortest lactation time of all mammals? Suckling lasts only 3-5 days after birth.

Suckling lasts only three to five days after birth. This makes the pup of the hooded seal the fastest suckling mammal compared to other mammals. During the suckling period, the pup drinks up to 10 litres of the high-fat content milk per day1,8. 

At birth, the pup weighs around 24 kilograms and is about 1 metre long1,2. After the suckling period, the pup will weigh about 48 kilograms. In other words, within five days, the pup doubles its weight (and gains about 7 kilograms a day)2,11. The pup first stays in the ‘nursing area’ for a while, but then starts learning to swim, dive and forage independently8. They do this based on their instincts.

Natural enemies of the hooded seal

Hooded seals are on the menu of polar bears. Killer whales could also be possible predators of the hooded seal, but this has not yet been observed. Greenland sharks can feed on young hooded seals2,11.

1. ( Hooded Seal; NOAA Fisheries; 2022)
https://www.fisheries.noaa.gov/species/hooded-seal

2. (Hooded Seal; IUCN RedList; 2015)
https://www.iucnredlist.org/species/6204/45225150

3. (Vulnerable species; dictionary; 2012)
https://www.dictionary.com/browse/vulnerable

4. (Polygyn, dictionary; 2012)
https://www.dictionary.com/browse/polygyny

5. (Hooded Seal;Marine Species Identification Portal; n.d.)
http://species-identification.org/species.php?species_group=marine_mammals&menuentry=soorten&id=49&tab=beschrijving

6. (Hooded Seal; Discovery of the Sound in the Sea; n.d.)
https://dosits.org/galleries/audio-gallery/marine-mammals/pinnipeds/hooded-seal/?vimeography_gallery=115&vimeography_video=653017743

7. (Hooded Seal; Oceanwide; n.d.)
https://oceanwide-expeditions.com/to-do/wildlife/hooded-seal

8. (Hooded Seal: Cystophora cristata; 2009)
https://www.sciencedirect.com/science/article/pii/B9780123735539001322

9. (Hooded seal Cystophora cristata foraging areas in the Northeast Atlantic Ocean-Investigated using three complementary methods; 2017)
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0187889

10. (Cystophora cristata hooded seal; Animal Diversity Web; 2010)
https://animaldiversity.org/site/accounts/information/Cystophora_cristata.html

11. (Hooded Seal; Norwegian Polar Institute; n.d.)
https://www.npolar.no/en/species/hooded-seal/

12. Thomas A. Jefferson, Marc A. Webber and Robert L. Pitman, in Marine Mammals of the World  (Second Edition), 2015

Authors:
Vivien Burmann

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Hooded seal births pup on Vlieland

Geschreven door Marco Boshoven op . Gepost in Nieuws.

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On the morning of Monday 27 March, a hooded seal gave birth to a pup on the beach of Vlieland. The hooded seal is a seal species that occurs naturally around the polar region, so that makes this very exceptional and special. After consultation with Sealcentre Pieterburen and the local seal guard, police and army have closed the area to the public for the time being. However, this is of limited duration and the centre is concerned about long-term conditions for the pup. Therefore, the centre calls for the animals to rest.

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On Monday 27 March, seal guard Willem made a very special discovery on the beach of Vlieland: a hooded seal that had recently given birth to a pup on the beach of Vlieland. Never before had this occurred. Hooded seals are native to the polar region and have one of the shortest nursing periods of all seal species: only four days on average. Therefore, the we are so gratefull that the local police and the army closed off the area around the mother and pup for the time being. Hopefully, the two will be able to get through the suckling period undisturbed.

The short suckling period will be followed by a period of fasting for the young animal, during which it will occasionally ingest some fluids through the ice it normally lies on. Then the animal goes hunting in the open waters of the polar region. These conditions are obviously lacking here. The centre is therefore concerned about how the pup will fare afterwards. Either way, it will be important to give the animals rest, and the centre makes the appeal to do so. Moreover, it is working with police and army to find a solution to keep the area closed for longer.


The hooded seal is a seal species listed as "vulnerable" on the IUCN red list. They live mainly around Greenland. Every now and then, young animals sometimes end up elsewhere. Several hooded seals have also been taken in the Netherlands, but 3 times in the past 10 years. In 2013, a young hooded seal came into Sealcentre Pieterburen and in 2014 and 2018 at A Seal in Stellendam.

Photo credit: Gerard Koster Joenje, vlielandplaatjes.nl

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European Association for Aquatic Mammals

Geschreven door Marco Boshoven op . Gepost in Nieuws.

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Ana, onze Hoofd Dierengeneeskunde, Zorg & Wetenschap en Sara, Stagiare Dierenarts woonden deze week de conferentie van de European Association of Aquatic Mammals (EAAM) bij. Beiden gaven een presentatie over hun onderzoek, gebruikte methoden en eerste bevindingen. Dat Ana en Sara het Zeehondencentrum vertegenwoordigen op de conferentie voor het welzijn en behoud van zeezoogdieren door middel van onderzoek, medische zorg, opleiding, onderwijs, behoud, beheer en activiteiten – dáár zijn we erg trots op!

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Onderzoek Sara

Congenital disorders in harbour (Phoca vitulina) and grey seals (Halichoerus grypus) admitted into rehabilitation from the Dutch Wadden sea 

Congenital disorders are functional or structural defects that are present at birth. Monitoring of birth defects in wildlife can provide conservationists with information about the status of that population and can help with the detection of emerging teratogens. In marine mammals, there are few reports on congenital abnormalities, which are mostly found during postmortem examinations. 

Harbour (Phoca vitulina) and grey seal (Halichoerus grypus) populations of the Dutch Wadden sea are stable and considered healthy. The current study summarizes information on sporadically appearing congenital or potentially congenital abnormalities in harbour and grey seals between 2014 and 2022. All animals were admitted into rehabilitation at Sealcentre, Pieterburen, in The Netherlands. We focused on the diagnostic methods and outcomes of each individual. The diagnoses were based on physical examination, clinical symptoms, and diagnostic imaging. These cases included melanism, albinism, microphthalmia, esophageal stenosis, impaired swallowing reflex, vestibular disease, dwarfism, hiatal hernia, cleft lip, arthrogryposis, and megaesophagus. During the study period, a total of 2739 seals were admitted into rehabilitation. The prevalence of congenital disease in our study was 0.62%. 

Onderzoek Ana

Gut microbiome of stranded harbour seals (Phoca vitulina) admitted for rehabilitation. 

In the Netherlands, the Sealcentre Pieterburen rehabilitates an average of 250 grey seals (Halichoerus grypus) and harbour seals (Phoca vitulina) per year. Being held in temporal captivity for rehabilitation might have an effect on the seals microbiome, and our study aimed to understand this effect in the gut microbiome of stranded harbour seals and the main factors contributing to it. We investigated the distal gut microbiome of two large cohorts (pups and weaners) of stranded harbour seals that were admitted for rehabilitation at the Sealcentre. The gut microbiome of young harbour seals stranded in the Netherlands is composed of Proteobacteria, Firmicutes, Bacteroidota, Fusobacteriota, Campylobacterota, and Actinobacteriota, and corresponds with the main core phyla described for this species in other parts of the world. The alpha diversity (richness and Shannon diversity) of the pup’s microbiome increased significantly during rehabilitation, while there were no significant changes in the weaners. Beta diversity of both pups’ and weaners’ gut microbiome was different before and after rehabilitation, with age and sex as main factors. We conclude that there was an important change in the microbiome of stranded harbour seals that were admitted to the Sealcentre.

Ana Rubio-Garcia1*, Aldert L. Zomer2 , Ruoshui Guo2, John W.A. Rossen3,4,5, Jan H. van Zeijl6, Jaap A. Wagenaar 2,7 , and Roosmarijn E.C. Luiken 2 

1. Veterinary and Research Department, Sealcentre Pieterburen, Pieterburen, The Netherlands 

2. Division of Infectious Diseases and Immunology, Utrecht University Faculty of Veterinary Medicine, Utrecht, The Netherlands 

3. Department of Medical Microbiology and Infection Prevention, University Medical Center Groningen, Groningen, The Netherlands 

4. Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT, USA. 

5. Laboratory of Clinical Microbiology and Infectious Disease, Isala hospital, Zwolle, The Netherlands. 

6. Department of Medical Microbiology Friesland and Noordoostpolder, Certe, Leeuwarden, The Netherlands 

7. Wageningen Bioveterinary Research, Lelystad, The Netherlands 

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  • Onderzoek Sara

  • Onderzoek Ana

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Studio Ditte

Geschreven door Marco Boshoven op . Gepost in Nieuws.

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Wat is ie leuk geworden: de zeehondenprint die Studio Ditte speciaal voor ons heeft ontwikkeld. En nog leuker, het kan bij jou thuis aan de muur hangen! Studio Ditte is een bewust merk dat onder andere behang ontwikkelt. Speciaal voor ons hebben ze dit zeehondenbehang ontworpen. En per rol gaat er €5,- naar ons centrum. Daar zijn we natuurlijk erg blij mee, ontzettend bedankt! Het zeehondenbehang is vanaf nu te koop via de webshop van Studio Ditte en via verschillende winkels.

Lees meer over onze samenwerking op het blog van Studio Ditte here. 

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zadelrob

Harp seal

Geschreven door Marco Boshoven op . Gepost in Zeehondensoorten.

Knowledge repository

Scientific name: Pagophilus groenlandicus
Family: Phocidae
Size: male: 1.90 meter; female: 1.80 meter
Weight: male 140 kilos; female 130 kilos
Habitat: Northwest Atlantic Ocean and the Arctic region
Endangered status: not endangered

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  • zadelrob

  • zadelrob

  • Zadelrob in Zeehondencentrum

  • Zadelrob in zeehondenopvang

"Swallowing stones helps the harp seal with going for a quick deep dive."

External features of the harp seal

The harp seal is a medium-sized seal species. Their body shape is somewhat elongated. The species has a pointed snout with eyes that are close together. But the most recognizable thing about the species is the saddle-shaped marking on their back. The species is therefore also called saddleback seal. In addition to the dark marking on the back, the harp seal also has a dark head.

Gender differences

Males are slightly larger than the females and have a more distinct color difference in their fur. In males, the saddle-shaped marking is dark and very noticeable, because the rest of the body is white. In females, the color sometimes differs from dark to gray and from white to light gray. Furthermore, there is little difference in appearance between males and females.

Distribution and status

Although they all belong to the same species, scientists distinguish three different populations of harp seals in the North Atlantic and the Arctic Ocean. The difference between these populations is mainly in the location where they birth their pups. The three populations are those of the Northwest Atlantic, the Northeast Atlantic and the Barents Sea.

The Northwest Atlantic population is further divided into two major groups: the 'Front' herd which births their pups off northern Newfoundland and southern Labrador, and the 'Gulf' herd that gives birth in the southern Gulf of St. Lawrence.

With over 7 million animals wordwide, the harp seal is not considered endangered. In fact, populations are growing in certain areas. Traditionally, the harp seal was also found in the Baltic Sea, but they have been eradicated there.

Diet and foraging

Like most seal species, the harp seal is "opportunistic". That means they eat whatever food is best to grab at the time. They don't make a big deal about it.

Did you know...

Harp seals in migration can cover as much as 5,000 kilometres a year? That's as far as you would walk from the Netherlands to Egypt.

Harp seals make long migrations during the year. Immediately after mating, harp seals go on a migration, eventually always returning to the mating and suckling grounds.

It is very typical of this species to swim long distances during the year. They follow the edge of the ice and the prey they can find there. So depending on where they are, their main prey also varies. Research has sometimes shown that they eat at least 67 species of fish and 70 species of invertebrates.

The first food for young harp seals are usually swimming crustaceans, such as krill and razor clams. Once the seals are older and can dive deeper, crustaceans, squid and fish are eaten.

Behaviour of the harp seal

Harp seals are very social. They can always be found in small groups on the ice, but also are together in the water. It is not known whether they also hunt in groups.

In the first period after suckling, the pups are alone for a while, but later they join the older animals. At that age, they also have to be very careful not to be caught by polar bears or arctic foxes. Once they become adults, they are no longer bothered by these, but they are still hunted by orcas and large shark species, such as the greenland shark.

Reproduction in harp seals

Mating behaviour

When the female finishes suckling the pup, she can mate immediately. The males know this. Hence, they fight with other males on the ice during this period for the females. Eventually, she mates in the water with the male of her choice. Immediately after mating, migration starts.

Diapause and pregnancy

The fertilised egg is not transferred to the uterus until three to four months after fertilisation. This is called diapause. After that, a harp seal female is pregnant for eight months.

Pups

When harp seals are born, they weigh an average of 11 kilos and are about 75 centimetres long. Newborn harp seals have a white coat (the lanugo coat), which keeps them warm on the ice. After the mother finishes suckling, the white fur falls out and they develop a silvery fur with a few dark spots. This is called beater-fur.

Did you know...

That when harp seal pups learn to swim, they hit the water with their tails?

The name beater does not refer to the fur, however, but to the fact that at this stage, puppies learn to swim and they hit the water with their tails. They keep this fur for the rest of their first year. After that, the fur becomes more spotted and the seal is called a "bedlam". As the seal ages, it develops more spots, until they reach adulthood. Then the spots disappear. However, some females will keep spots all their lives.

Birth and nursing period

Harp seals take advantage of the brief moment in the year when there is a thick layer of pack ice. On this layer of ice they have the "land" they need to have their young.

The suckling period lasts about 10 to 12 days. During this time, the pup gains more than 20 kilos. Then the mother leaves the pup and it is left alone on the ice. Here the process of moutling to the beaterfur begins. They may be left like this for up to 6 weeks without food. In these extreme cases, they lose half their body weight again. Eventually, hunger causes them to search for food in the cold arctic waters.

Harp seal in Sealcentre Pieterburen

In October 2016, we caught a harp seal. Very exceptional, because normally this seal species is are not found in the Netherlands. She was found severely weakened near Den Oever. She weighed only 60 kilos, while an adult harp seal should weigh between 140-150 kilos. Fortunately, she was eventually able to recover and be released. And that was quite a special moment. Read the story of Summer the harp seal here.

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Lungworms

Geschreven door Marco Boshoven op . Gepost in Informatie over zeehonden.

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In its first year of life, a seal is susceptible to infection by lung worms. After being weaned, young seals will go out and start hunting for prey by themselves. This is when they often contract lung worm infections. A number of them will get so sick, that they would not be able to survive without help. 

See also

  • Longwormen bij gewone zeehond

  • Longwormen bij zeehonden

Lung worms are parasites that can severely damage the lungs – they eat the tissues in the lungs and reproduce there, causing more and more damage in the process.

The seal will experience shortness of breath and the damaged lungs are more susceptible to pneumonia or other bacterial infections. The shortness of breath also prevents a seal from staying under water long enough to hunt. This leads to starvation, weakness, and possibly death.

Seals are exposed to lung worm through the food they eat. For example, a fish might have been infested with lung worm when it was eaten by a seal. From the stomach, the lung worms will travel through the blood stream to the lungs, where they grow and produce larvae. Infected seals will start coughing, expelling the microscopic larvae from their lungs.

These larvae are then ingested by the seal, thus entering the host’s digestive tract. When the seal defecates, the larvae are released into the sea, where they can infect small sea creatures and grow. The infected sea creatures are eaten by seals, at which point the infection cycle restarts. If an infected animal is found on time, it can be treated. A seal with lung worm infection can be recognised by symptoms such as laboured breathing, a high back, and blood around the mouth from coughing.

Usually a seal with a lung worm infection will need to be rehabilitated for two to three months; once a seal has been cured, it will be resistant to this parasitic infection for the rest of its life.

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Lungworms

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Publications

Geschreven door Marco Boshoven op . Gepost in Wetenschappelijk onderzoek.

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Publications

Laura Verga, Marlene G. U. Sroka, Mila Varola. Stella Villanueva and Andrea Ravignani. (2022). Spontaneous rhythm discrimination in a mammalian vocal learner. Biology Letters, 18:20220316https://royalsocietypublishing.org/doi/full/10.1098/rsbl.2022.0316

David Ebmer, Stephan Handschuh, Thomas Schwaha, Ana Rubio‑García, Ulrich Gärtner, Martin Glösmann, Anja Taubert and Carlos Hermosilla. (2022). Novel 3D in situ visualization of seal heartworm (Acanthocheilonema spirocauda) larvae in the seal louse (Echinophthirius horridus) by X-ray microCT. Scientific Reports, 12:14078  https://www.nature.com/articles/s41598-022-18418-y

Anna Salazar-Casals; Koen de Reus; Nils Greskewitz; Jarco Havermans; Machteld Geut; StellaVillanueva; Ana Rubio-Garcia. Increased Incidence of Entanglements and Ingested Marine Debris in Dutch Seals from 2010 to 2020. (2022) Oceans, Vol 3, Issue 3, 389-400. https://doi.org/10.3390/oceans3030026

Jörg Hirzmann, David Ebmer, Guillermo J. Sánchez‑Contreras, Ana Rubio‑Garcia, Gerd Magdowski, Ulrich Gärtner, Anja Taubert and Carlos Hermosilla. The seal louse (Echinophthirius horridus) in the Dutch Wadden Sea: investigation of vector-borne pathogens (2021) Parasites & Vectors 14:96 https://doi.org/10.1186/s13071-021-04586-9

Abbo van Neer, Ana Rubio-Garcia , Stephanie Gross, Anna Salazar-Casals, Alberto Arriba-Garcia2 Peter Wohlsein and Ursula Siebert. An innovative approach for combining marking of phocid seals with biopsy sampling using a new type of livestock ear tags. (2020) Journal of Marine Animals and Their Ecology Vol 12, Issue 1, 2020.

Anna Salazar-Casals, Klaas Marck, Tijmen de Jong, James Collins, Joost Dorgelo, Pier Prins, and Ana Rubio-Garcia Retrospective study of surgical treatment of refractive osteomyelitis and infectious arthritis in the flippers of seals in The Netherlands. (2020) Journal of Zoo and Wildlife Medicine 51(3), 598-605, (16 November 2020). https://doi.org/10.1638/2018-0221

Anna Salazar-Casals, Alberto Arriba-Garcia, Antonio A. Mignucci-Giannoni, John O’Connor, Ana Rubio-Garcia. Hematology and serum biochemistry of harbor seal (Phoca vitulina) pups after rehabilitation in the Netherlands (2020) J. of Zoo and Wildlife Medicine, 50(4):1021-1025 https://doi.org/10.1638/2018-0098

Rubio-Garcia, A., Rossen, JWA., Wagenaar, JA., Friedrich, AW., van Zeijl, JH. Livestock-associated meticillin-resistant Staphylococcus aureus in a young harbour seal (Phoca vitulina) with endocarditis (2019) Veterinary Record Case Reports 7: e000886. https://doi.org/10.1136/vetreccr-2019-000886

Ravignani A, Kello CT, de Reus K, Kotz SA, Dalla Bella S, Méndez-Aróstegui M, Rapado-Tamarit B, Rubio-Garcia A, de Boer B. Ontogeny of vocal rhythms in harbor seal pups: an exploratory study (2019) Current Zoology, Volume 65, Issue 1, Pages 107–120, https://doi.org/10.1093/cz/zoy055

Maarten J. Gilbert*, Aldert L. Zomer, Arjen J. Timmerman, Mirlin Spaninks, Ana Rubio-Garcia, John Rossen, Birgitta Duim, and Jaap A. Wagenaar. Campylobacter blaseri sp. nov., isolated from common seals (Phoca vitulina) (2018) International Journal of Systematic and Evolutionary Microbiology. DOI 10.1099/ijsem.0.002742 https://library.wur.nl/WebQuery/wurpubs/537778

Ravignani A*, Gross S*, Garcia M, Rubio-Garcia A, de Boer B. How small could a pup sound? The physical bases of signalling body size in harbour seals. (2017) Current Zoology, 2017, 1–9. Doi: 10.1093/cz/zox026 https://academic.oup.com/cz/article/63/4/457/3603549

Ulrich SA, Lehnert K, Rubio-Garcia A, Sanchez-Contreras GJ, Strube C, Siebert U. Lungworm seroprevalence in free-ranging harbour seals and molecular characterisation of marine mammal MSP. (2016) International journal for parasitology: parasites and wildlife. Doi:10.1016/j.ijppaw.2016.02.001 https://www.sciencedirect.com/science/article/pii/S2213224416300062

Bodewes R*, Rubio García A*, Brasseur SM*, Sanchez Conteras GJ, van de Bildt MWG, Koopmans MPG, Albert D. M.E. Osterhaus, Thijs Kuiken. Seroprevalence of Antibodies against Seal Influenza A(H10N7) Virus in Harbor Seals and Gray Seals from the Netherlands. (2015) PLoS ONE 10(12): e0144899. doi:10.1371/journal. pone.0144899 http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0144899

Rubio García A, Sánchez Contreras GJ, Juliá Acosta C, Lacave G, Prins P, Marck K. Surgical treatment of osteroarthritis in harbor seals (Phoca vitulina).(2015) Journal of Zoo and Wildlife Medicine 46(3):553-559. http://www.bioone.org/doi/abs/10.1638/2014-0229.1

Woodman S, Gibson A.J, Rubio Garcia A, Sanchez Contreras G, Rossen J.W, Werling D, Offord V. (2015) Structural characterisation of Toll-like receptor 1 (TLR1) and Toll-like receptor 6 (TLR6) in elephant and harbor seals. Veterinary Immunology and Immunopathology 169, DOI: 10.1016/j.vetimm.2015.11.006 https://www.sciencedirect.com/science/article/pii/S0165242715300210

Bodewes R, Sánchez Contreras GJ, Rubio García A, Hapsari R, van de Bildt MWG, Kuiken T, Osterhaus ADME. (2015) Identification of DNA sequences that imply a novel gammaherpesvirus in seals. Journal of General Virology, 96, 1109–1114 DOI 10.1099/vir.0.000029 http://jgv.microbiologyresearch.org/content/journal/jgv/10.1099/vir.0.000029

Reichel M, Muñoz-Caro T, Sánchez Contreras GJ, Rubio García A, Magdowski G, Gärtner U, Taubert A, Hermosilla C. (2015) Harbour seal (Phoca vitulina) PMN and monocytes release extracellular traps to capture the apicomplexan parasite Toxoplasma gondii. Developmental and Comparative Immunology (2015), doi: 10.1016/j.dci.2015.02.002 https://www.sciencedirect.com/science/article/pii/S0145305X15000257

Bodewes R, Hapsari R, Rubio García A, Sánchez Contreras GJ, van de Bildt MWG, de Graaf M, Kuiken T, Osterhaus ADME. (2014) Molecular epidemiology of seal parvovirus, 1988-2014. PLoS ONE 9(11): e112129. doi:10.1371/journal.pone.0112129 http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0112129

Bodewes R, Rubio García A, Wiersma LCM, Getu S, Beukers M, Schapendonk CME, van Run PRWA, van de Bildt MWG, Poen MJ, Osinga N, Sánchez Contreras GJ, Kuiken T, Smits SL, Osterhaus ADME. (2013) Novel B19-Like Parvovirus in the Brain of a Harbor Seal. PLoS ONE 8(11): e79259. doi:10.1371/journal.pone.0079259 http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0079259

Bodewes R, Morick D, van de Bildt MWG, Osinga N, Rubio García A, Sánchez Contreras GJ, Smits SL, Reperant LAP, Kuiken T & Osterhaus ADME. (2012). Prevalence of phocine distemper virus antibodies: bracing for the next seal epizootic in north-western Europe. Emerging Microbes and Infections (2013) 2, e3; doi:10.1038/ emi.2013.2 https://www.nature.com/articles/emi20132

Anichini M, de Reus K, Hersh TA, Valente D, Salazar-Casals A, Berry C, Keller PE, Ravignani A. 2023 Measuring rhythms of vocal interactions: a proof of principle in harbour seal pups. Phil.Trans. R. Soc. B 378: 20210477.https://doi.org/10.1098/rstb.2021.0477  

Ravignani, A., Anichini, M., Sroka, M., Varola, M., Salazar Casals, A., de Reus, K., & Verga, L. (2022). Vocal learning, chorusing seal pups, and the evolution of rhythm. The Journal of the Acoustical Society of America, 152(4), A275-A275.

Koen de Reus, Daryll Carlson, Alice Lowry, Stephanie Gross, Maxime Garcia, Ana Rubio-Garcia, Anna Salazar-Casals, Andrea Ravignani; Vocal tract allometry in a mammalian vocal learner. J Exp Biol 15 April 2022; 225 (8): jeb243766. doi:https://doi.org/10.1242/jeb.243766

Ravignani, A., Torres Borda, L., Rasilo, H., Salazar Casals, A., & Jadoul, Y. (2022). Parselmouth for bioacoustics: Analysis pipelines for seal vocalizations. The Journal of the Acoustical Society of America, 151(4), A29-A29.

Torres Borda, L., Jadoul, Y., Rasilo, H., Salazar-Casals, A., & Ravignani, A. (2021). Vocal plasticity in harbour seal pups. Philosophical Transactions of the Royal Society of London, Series B: Biological Sciences, 376(1840): 20200456. doi:10.1098/rstb.2020.0456.

Hoeksema, N., Verga, L., Mengede, J., Van Roessel, C., Villanueva, S., Salazar-Casals, A., Rubio-Garcia, A., Curcic-Blake, B., Vernes, S. C., & Ravignani, A. (2021). Neuroanatomy of the grey seal brain: Bringing pinnipeds into the neurobiological study of vocal learning. Philosophical Transactions of the Royal Society of London, Series B: Biological Sciences, 376: 20200252. doi:10.1098/rstb.2020.0252.

Gilbert MJ, IJsseldijk LL, Rubio-García A, Gröne A, Duim B, Rossen J, Zomer AL, Wagenaar JA. 2020 After the bite: bacterial transmission from grey seals (Halichoerus grypus) to harbour porpoises (Phocoena phocoena). R. Soc. Open Sci. 7:192079.http://dx.doi.org/10.1098/rsos.192079 

Ravignani, Andrea, Christopher T. Kello, Koen de Reus, Sonja A. Kotz, Simone Dalla Bella, Margarita Méndez-Aróstegui, Beatriz Rapado-Tamarit, Ana Rubio-Garcia, and Bart de Boer. “Ontogeny of vocal rhythms in harbor seal pups: an exploratory study.” Current Zoology 65, no. 1 (2019): 107-120.

Jo WK, Pfankuche VM, Lehmbecker A, et al. Association of Batai Virus Infection and Encephalitis in Harbor Seals, Germany, 2016. Emerging Infectious Diseases. 2018;24(9):1691-1695. doi:10.3201/eid2409.171829.

Melero, Mar, Víctor Rodríguez-Prieto, Ana Rubio-García, Daniel García-Párraga, and José Manuel Sánchez-Vizcaíno. “Thermal reference points as an index for monitoring body temperature in marine mammals.” BMC research notes 8 (2015): 1-8.

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Pup roept

Sound of a seal

Geschreven door Marco Boshoven op . Gepost in Wetenschappelijk onderzoek.

Knowledge repository

See also

  • Sound of a seal

  • Hoe communiceren zeehonden?

  • Opname geluid zeehond

  • Zeehonden communicatie

Postdoctoral research into vocal learning in animals

Grey seals and Common seals are apparently part of a very specific group of animals. Animals that, just like humans, have the ability to develop their voice over the course of their life. This phenomenon is called ‘vocal learning’. Other animals that possess this ability are parrots, passerine birds, and bats. An extraordinary example of vocal learning in seals is a seal called Hoover, who was kept in Boston’s New England Aquarium. Hoover was raised by humans and learned to copy human speech. Andrea Ravignani did his postdoctoral research at the Sealcentre and investigated the ‘crying’ of seal pups.

Read more about his research group.

Onderzoeker Andrea Ravignani

Why do people talk? And why do seal pups cry?

Andrea Ravignani is doing postdoctoral research at Sealcentre Pieterburen that is funded by the prestigious Marie Curie Scholarship. Andrea is an Italian scientist who is fascinated by the question of how animals – and humans – learn to produce sounds. As a part of his research in Pieterburen, he records the sounds of seal pups every day; the so-called ‘crying’. Andrea uses these recordings to then see if there is a development in the production of these sounds.

Have you ever noticed how babies (human pups) begin with crying, then transition to incoherent babbling, and how this slowly changes into language? Something similar happens in seals. The sound – or voice – of each seal is very different, and their voices also change as they age. In fact, it looks like Grey and Common seals are members of a special group of animals that, like humans, have the ability to shape their voices over the course of their lives. This ability is called ‘vocal learning’. Other animals that have this ability are parrots, passerine birds and bats.

An exceptional example of this ability in seals is the aforementioned seal named Hoover. Hoover was an orphaned pup who was taken in and raised by humans in Boston. Before he was relocated to the New England Aquarium, he had learned to mimic human speech. Hearing Hoover speak his former owner’s catchphrases is truly bizarre. You can hear how he sounds in the YouTube video “Hoover the Talking Seal”. Seals learn to make sounds through imitation, which they then adapt and change into their very own voice. Because of that, they might be the animal closest to us humans when it comes to ‘vocal learning’.

Andrea’s research is important for two reasons. On the one hand it helps us to gain a better understanding of seals and what is important for them in the first phases of their life. On the other hand it gives us a glimpse into the evolution of humans. Human evolution is very difficult to reconstruct without a time machine, especially when it comes to the evolution of speech and language. Communication in seals is a completely new field of study.

Special research findings vocal learning

December 2018 - Seal pups communicate just like us

In December 2018, Dr Andrea Ravignani published his discovery that seal pups adjust their communication based on the sounds of other pups. A sense of rhythm and timing had never before been demonstrated in seals. His work gives an insight into the vocal communication of humans, as well as seals.

Research conducted by Dr Andrea Ravignani from the Artificial Intelligence Lab of the Vrije Universiteit Brussel at Sealcentre Pieterburen was the first to show that seal pups exhibit complex communication behaviour. He observed that seal pups adjust their sounds and especially their rhythm to what another pup is doing. Said simply: they take turns making sounds. However simple this may seem, it has never before been demonstrated in seals and it characterises animals that use complex communication methods. The study will be published in the Journal of Comparative Psychology.

Ravignani: “Us humans often consider our communication to far more complex than that of other animals. However, what we are seeing in seal pups is astonishing. Even at four weeks old, seals seem to demonstrate a very precise and flexible timing in their communication. To an extent this is very comparable to the alternation we see in human conversations or in a musical canon.”

The discovery fits in well with a study conducted by the Sealcentre into the behaviour of mothers and pups in the wild, which showed that pups suckle with several different mothers. It is therefore important that pups stand out between their peers and adjust their calls.

Ravignani: “This finding was relatively unexpected and even seems counterintuitive at first. Communication in Common seals is usually relatively vertical – between mother and pup, not between different pups. However, what we see here is horizontal communication: the rhythm of one pup determines the rhythm of another pup. While this is surprising within the established knowledge of mother-pup interactions in Common seals, my findings fit very well in the behavioural research that the Sealcentre is conducting with the University of Groningen.”

The study is part of a two-year research programme that Ravignani is conducting with the support of the Marie Curie Scholarship.

October 2021 - Seals and the evolution of human speech

Seals are good at learning sounds. The 'talking seal' Hoover could even imitate human speech. But can young seals already adapt their sounds to the environment? Researchers from the Max Planck Institute for Psycholinguistics, the Vrije Universiteit Brussel and the Pieterburen Seal Centre studied seal pups a few weeks old. When the seal pups heard louder ambient sounds, they themselves called out with a lower pitch. This makes seals very suitable for research into the evolution of human speech.

The seal Hoover had been taken in as a pup by an American family. Even after he had already been moved to an aquarium, he continued to mimic human speech: he barked at visitors in his gruff voice (“Come over here”). Seals therefore belong to the small group of mammals that can learn to imitate sounds, also called 'vocal learning'.

It is even more special if animals can adjust the pitch of their voices: an important feature of human speech. Senior researcher Andrea Ravignani says: "By studying these extraordinary mammals, we hope to eventually better understand how humans evolved speech and why we ourselves are such a talkative species." What Ravignani and his colleagues particularly wanted to know: could seals adjust their pitch from an early age?

Sounds of the Wadden Sea

The researchers decided to study eight seal pups from 1 to 3 weeks old. The seals were already staying at seal centre Pieterburen to gain strength. After 2-3 months in the sanctuary, they were released into the wild. To investigate whether the seal pups could adapt their sounds to ambient noise, the biologists first made recordings of natural ambient sounds of the Wadden Sea. These sounds were played in the seals' enclosure for a few days, at three different sound levels (from no sound to 65 dB). The pitch of the ambient sounds was similar to that of the seal sounds. The researchers also made recordings of the seal sounds. Would the pups adapt to the ambient noise and call higher or lower?

When ambient sounds were louder, the seals called with a lower pitch. At the loudest sounds, their pitch also remained the most stable. One seal also clearly showed the 'Lombard' effect: it started calling louder when ambient sounds were louder. This effect is also typical of human speech: people start talking louder when there is ambient noise, so they can be better understood. But the seals did not call out more often or longer at different noise levels.

Brain pathways

So even very young seals can already adapt their sounds to the environment by calling at a different pitch. That ability they share with humans and bats is unusual for a mammal. Other animals only call louder in similar experiments.

"The seal pups have much better control over their vocalisations than we thought,", says Ravignani "And they already have control over their voice when they are only a few weeks old. That is unique in the animal world. We thought only humans had a direct connection between the cerebral cortex and the larynx. But seals therefore seem to have these connections too. That brings us another step closer to unravelling the mystery of human speech."

Veterinarian and researcher at seal centre Pieterburen Anna Salazar Casals added: "As a rehabilitation centre, we are happy to collaborate on research, in order to understand the animals better and protect them even better. We can use these new insights, for example, when setting up new shelter facilities or determining what resting areas in the wild should comply with."

April 2022 - Anatomical studie confirms: seals learn to make sounds

Seals are good at learning sounds. The 'talking seal' Hoover could even imitate human speech. But can young seals already adapt their sounds to the environment? Researchers from the Max Planck Institute for Psycholinguistics, the Vrije Universiteit Brussel and the Pieterburen Seal Centre studied seal pups a few weeks old. When the seal pups heard louder ambient sounds, they themselves called out with a lower pitch. This makes seals very suitable for research into the evolution of human speech.

Most animals make sounds that fit their body size. A larger animal will sound lower because the larynx is longer: the air-filled canal in the neck where the vocal cords are located. But seals do not always sound the way they look. Sometimes they sound lower and therefore bigger, for example to impress a rival. Or higher and thus smaller, for instance to get more attention from their mother. Are these animals good at learning sounds (vocal learning) or has their larynx adapted to be more flexible?

Sealcentre Pieterburen

To answer this question, PhD student Koen de Reus and senior researcher Andrea Ravignani from the MPI worked with researchers from Sealcentre Pieterburen. The team measured the larynxes and body size (length and weight) of 68 young seals (up to 12 months old) that had died before or after a rescue attempt. The researchers also analysed previously recorded seal sounds, confirming the seal's wide range in pitch.

De Reus and Ravignani found that the length of the seal larynx matched their body size exactly. So there were no anatomical explanations for their vocal talents. According to the researchers, only the vocal learning ability of seals can explain why they do not always sound the way they look.

Vocal learning ability

"Animals with vocal learning ability will sound differently than expected based on their body size, but the length of their larynx matches their body size. This combined acoustic and anatomical data can help us find more animals like this,", says de Reus "Studying multiple animal species with this ability is also going to help us find the biological basis of vocal learning. And possibly it will also provide insights into the evolution of complex communication systems such as speech.".

"The more we study seals, the more we see that they can tell us something about human speech,", Ravignani adds.

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History of seals

Geschreven door Marco Boshoven op . Gepost in Informatie over zeehonden.

Knowledge repository

Did you know that seals were hunted in the Netherlands*? Seals have been killed for their fur and meat for centuries, but there came a time when bounties were even paid for simply killing these animals. We can hardly imagine it anymore, but it was only after 1962 that seal hunting was officially banned and the seals were given a protected status. On this page you can read more about the history of seals in the Netherlands and how our image of the seal has changed over the centuries.

*Most of this history is about the common seal. The grey seal probably hadn't been seen in the Netherlands for centuries - until their return in the 1980s.

See also

The seal as a source of food

Until the Middle Ages, people caught seals in the Netherlands for their meat. They actually ate seal meat! You could buy the seals at the fish market. The paintings by Frans Snijders from the 17th century give you an idea of what such a fish market may have looked like at that time. In the 16th century, the need to eat seal meat disappeared, although people still occasionally ate the liver.

  • Schilderij Frans Snijders 17e eeuw

    Painting 1

  • Schilderij vismarkt 17e eeuw

    Painting 1.2

  • Schilderij zeehond 17e eeuw

    Painting 1.3

Three paintings by Frans Snijders about the fish market, from the 17th century. Can you find the seal(s) in each painting?

The seal as a fish thief

Bounty yacht in Zeeland

There was a turnaround at the end of the 16th century. Fishermen in Zeeland were of the opinion that seals were their competitor, because according to them seals ate too much fish. To protect the fisheries, Zeeland was the first to start paying a premium in 1591 if you killed a seal. The distribution of the premiums was tracked. For example, this documentation shows that more than 40,000 seal premiums were paid between 1591 and 1801!

Everyone was free to earn money by catching a seal. In Zeeland, there were specialized seal hunters. But if you happened to encounter seals in the rivers or along the coast as a fisherman, you could also hunt them (see image 2). Even islanders from Schiermonnikoog came all the way to Zeeland to hunt for seals. Zeeland finally stopped the seal premiums in 1857.

Prent uit 1582 over zeehonden en tarbotvangst

Print of seals and turbot fishing by Adriaen Collaert from 1582. On the left of the print you see how two seals are caught. Source. 

Seal hunting in other provinces

In 1610, Holland (nowadays North and South Holland) started with a premium to combat seals. Bounty hunting was considerably smaller: in South Holland, 40 seals were caught in the 12 years that the seal premium existed.

Seal hunting also existed in both Friesland and Groningen. No premiums were paid for it. Seal hunters used to live in Westernieland, a village close to Pieterburen. Documentation showed that between 1859 and 1899 they caught between 100 and 250 seals per year.

National seal bounty

In 1900, a national seal bounty started. The cause was again due to complaints from the fishing industry. Fishermen saw the seal as a common tern and destroyer of their fishing nets, although the exact damage caused by seals to the fishery had not been investigated. Despite the lack of evidence, the national seal bounty went ahead anyway. For example, the government gave you 3 florins for a killed female seal and 2.50 florins for a killed male seal.

Criticism of seal hunting

The image that people had of seals and the seal hunt eventually came under discussion during this period. At the end of 1920, the opposing voices became somewhat louder. Some people did not think it wise to spend state money on seal hunting during the general depression.

Other insights also emerged about nature and that animals can also have an indirect use. Even "harmful" animals - as was thought of the seal - have their role in nature. Nature and animal protection became increasingly important and the method of killing seals also received criticism.

Seal hunt with pens

However, this still had little impact on daily practice. Only the gruesome hunting with pens stopped on Terschelling. This form of hunting went as follows: a beam with sharp pins was placed at the tide line. Seals were frightened from a sandbar and fled into the water. There, they got into the pens and were injured. Hunting with a rifle and bat was still allowed (see image 3).

  • Zeehondenjacht

    Image 3

  • Zeehondenjacht

    Image 3

Image of children clubbing a seal from an early 20th century school book. Photo of pleasure hunters with their shot seals. Source: Seal hunt in the Netherlands 1591-1962

The hunt continued

Despite the criticism, bounty payments continued uninterrupted. In the period from 1900 to 1942 (with a stop for a number of years), between 800 and 1600 seals were killed per year. Seal hunting was abolished by the German occupiers in 1942, but resumed after World War II. In 1954, a new hunting law was even introduced in which all existing rules regarding hunting were canceled: the hunting season applied both throughout the year and throughout the country.

Sealant

Just as people used to heat whale blubber to make whale oil, this used to be done with seals. By heating the fat layer of a seal, a tear was created that people could use in different ways. After the Second World War, the demand for tear quickly declined again. Petroleum then became increasingly popular and took the place of seal tear.

Sealant was used for:

  • Fuel in lamps
  • A kind of oil for frying food
  • Grease to keep leather supple
  • Raw material for margerine and soap

The seal as a fashion trend

Before World War II, hunters shot young and older seals. This changed after the war. Back then, young seals were mainly hunted. The fur industry paid much better for a seal than the government did. According to Groninger Hendrik Teerling from the documentary Other Times you got 30 to 45 guilders for the fur of a young seal. People started to hunt seals for the fur industry.

Seal fur was fashionable. The sealskin has been used for clothing and shoes for centuries. But the demand for seal fur grew when the Groningen fur trader Van Daal & Meijer (1938 – 1973) came into the picture. The big breakthrough came after the war: the company had devised a processing process in which the seal skins did not become stiff, but remained flexible and soft. This lead made them one of the largest seal fur traders in the world.

Zeehondenbont

Image caption: Lady in seal fur coat, designed by Jacques Fath from the collection of Bonthandel Van Daal & Meijer (1950-1954). Source: Groninger Archieven.

The supply of sealskin from the Netherlands was not enough. Van Daal & Meijer expanded into seal hunting in Canada, Greenland and Iceland (see figure 5). There they hunted the hooded seal and the harp seal. After the seal hunting ban in the Netherlands after 1962, they continued to hunt seals abroad until the 1970s.

Vangplekken van zeehonden bij Canada, Groenland en IJsland

Map with trapping locations of various species of seals near Canada, Greenland and Iceland, from Bonthandel Van Daal & Meijer (1950-1954). Source: Groninger Archieven.

The seal as a protected species

People started to work to help the seal. Before the seal hunt stopped, seal rehabilitation had already started. Gerrit de Haan and Annie de Haan-Langeveld were the pioneers and were the first in Europe to set up a seal rehabilitation center (see video). This started in 1952 on the Wadden Island of Texel at the Texel Museum, which is now called Ecomare .

Video from Ecomare with video footage of founder Annie de Haan. Source: Youtube channel Ecomare Texel – De Koog.

In 1961  In 1961, the Wentzel family also started saving seals. They lived in the village of Uithuizen in the province of Groningen. After the death of Mrs. Wentzel, Lenie ’t Hart was asked to take over the seal sanctuary in 1971. That was the start of Sealcentre Pieterburen. You can read more about the history of Sealcentre Pieterburen here .

Zeehondenopvang in Uithuizen

René and Anneke Wentzel in their backyard where they rescued seals in Uithuizen. Source: Peter Wentzel.

Things went badly for the seals

Things went very badly for the seals when the seal rehabilitation centers on Texel and Uithuizen started. This can be clearly seen with a graph of the counts of seals in the Dutch Wadden Sea. From the year 1900 it can be seen that the number of seals has decreased enormously: from about 15,000 seals to about 2,000 seals in 1960. The fact that the seals were doing so badly was taken seriously by the government in the 1960s. In the end, the government decided to ban seal hunting in the whole of the Netherlands after 1962. 

Grafiek zeehondenpopulatie 20e eeuw in Nederlandse Waddenzee

Graph showing the number of seals in the Dutch Wadden Sea. The light blue line represents the harbor seal and arises from the dark blue line; the orange line represents the number of gray seals that returned in the 1980s.

Serious pollution of sea water

The number of seals in the Wadden Sea remained low. The seawater was seriously polluted and commercial shipping and water tourism caused a lot of disruption. The harmful substances PCBs in the water in particular had a negative influence on the reproduction of the seals.

After an outbreak of a virus in which half of the seals died in 1988 and in 2002, seals were given the opportunity to grow in numbers again – and they succeeded. There was more good news: grey seal re-established itself in the Wadden Sea in the 1980s. Conclusion: the seal has made a comeback!

The relationship between humans and seals has changed a lot over the past few centuries. It's actually amazing how differently we thought about seals compared to now. By changing our image of the seal and by committing ourselves to its protection, we as people ensured that we did not lose the seal in the Netherlands. One thing is clear from a look at history: we must ensure that the seals have a future. We will therefore continue to work for a healthy seal in a healthy sea. Day in day out. Are you in?

Sources:

  1. Zeehondenjacht in Nederland 1591 – 1962. Pieter ’t Hart.
  2. Aflevering Zeehondenjacht van het programma Andere Tijden (2004). https://anderetijden.nl/aflevering/472/Zeehondenjacht
  3. Het begin van de zeehondenopvang op Texel. https://www.ecomare.nl/ontdek-ecomare-op-texel/dieren/zeehonden-bij-ecomare/begin-zeehondenopvang-op-texel/
  4. Reijnders, P. J. H. 1986. Reproductive failure in common seals feeding on fish from polluted coastal waters. Nature 324:456-457
  5. Gewone en grijze zeehond in Waddenzee en Deltagebied, 1960 – 2020. https://www.clo.nl/indicatoren/nl123117-gewone-en-grijze-zeehond-in-waddenzee-en-deltagebied

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Sea lions (Otariidae)

Geschreven door Marco Boshoven op . Gepost in Informatie over zeehonden.

Knowledge repository

A family very close to seals (Phocidae) is the sea lion family. They may look very similar to seals at first glance, but there are big differences. Do you know the difference? On this page, you will get to know the sea lion family a little better.

See also

  • Zeeleeuwen

  • Zeeleeuw op strand

  • Zeeleeuwenpopulatie

Otariidae

The sea lion family is also known as eared seals. They derive this name from their auricles. In the scientific world, we call this family Otariidae. Like seals , sea lions belong to the order Carnivora, or carnivorous mammals. Bears, lions, wolves and walruses are also members of this order. Sea lions are carnivores. They hunt fish, crustaceans and shellfish in shallow coastal waters.

Sea lions, seals and walruses are often placed in a special group of marine mammals. This group is called the pinnepeds (Pinnipedia). You might have guessed it: this group gets their name from the shape of the legs. In these animals, the legs are very short, but with very long toes and fingers. This makes them look like they have fins.

How do you recognize sea lions

Sea lions are often confused with seals. Do you have any idea how you can actually distinguish a sea lion very easily? Their name (eared seals and Otariidae) kind of gives it away: the ears. You can see little auricles protruding from the side of their heads. Seals and walruses do not have these; they have holes as ears.

De lichaamsbouw van zeeleeuwen lijkt wel wat op dat van zeehonden. Ze hebben een lang lichaam met een grote borstkas. Ze zijn over het algemeen wat slanker gebouwd dan zeehonden, met een spitsere kop. De voorpoten van zeeleeuwen zijn een stuk langer dan die van zeehonden.

Sea lions can move a lot more smoothly over land than seals. This is because they can fold their rear flippers forward. By leaning on their front and rear flippers, they can simply walk on land. And when needed, for example to flee, they can even run quite fast!

You can usually clearly see the difference between males and females in adult sea lions. Males are a lot bigger, with a very large chest, thick neck and larger head. This distinct difference between males and females is called sexual dimorphism.

Did you know...

Sexual dimorphism can look very different in different animal species? In many birds, males are very colourful, while females have more camouflage colours. Also, it is not always the males that are bigger or more colourful than the females. In fact, many insect and spider species have larger, more colourful, or more venomous females.

Flying over the seabed

Sea lions are incredibly good swimmers. Just like other pinnipeds, for that matter. They just take a slightly different approach from seals and walruses. Seals and walruses use their hind flippers to gain speed and their front flippers to steer. Sea lions do the opposite.

Sea lions have very long front flippers. Instead of their rear flippers, they use these long front flippers to gain speed. They move their front flippers up and down, like wings. By doing this, they push themselves forward through the water. They then use their rear flippers to steer.

Because they swim this way, sea lions are a lot more agile than seals. But, they cannot swim as long and deep as seals.

Together in big groups

Sea lions are social animals: they often live together in huge groups. These groups are also called colonies. During the mating season, an entire colony often lies together on the coast. Within a colony, there are smaller groups consisting of a male and his harem. These harems can sometimes consist of dozens of females!

Especially when hunting, sea lions are a lot more social than seals. Sea lions often hunt schools of fish in groups. By working together, they can easily catch fish from schools. This is much more difficult for seals, which hunt alone.

Did you know...

Some sea lions are so good at hunting together that other animals take advantage of it too? Galápagos Sea Lions (Zalophus wollebaeki) go after whole schools of fish while hunting. Then birds, sharks and other sea lions often lurk as well. Once the Galápagos Sea Lions have chased the fish together, the other predators quickly snatch a few!

Where do sea lions live?

In the Pacific, sea lions are fairly widespread. They live mostly in tropical and subtropical seas (California and Galápagos, for example), but also in the more temperate and sub-Antarctic regions (such as South America and New Zealand).

Sea lions always mate and have their pups on land. Therefore, there are no species found in the Arctic. The only places in the Atlantic where sea lions live are the southern tip of the African continent, and along the South American coasts. So here in Europe, you cannot see sea lions in the wild.

How many sea lion species are there?

The family of sea lions (Otariidae) consists of 14 species in total. These are often divided into 2 groups based on their appearance. The fur seals or sea bears (Arctocephalinae) are slightly smaller and get their name from the longer fur around the chest and neck. In these animals, you can see an extreme size difference between males and females (sexual dimorphism). This group consists of eight species. The sea lions (Otariinae) are a bit larger, have smoother fur and have a somewhat smaller difference between males and females. This group consists of 6 species.

Did you know...

At the time of writing, there is an ongoing debate in science about the classification and designation within the sea lion family (Otariidae)? New analyses have shown that the division between fur seals (Arctocephalinae) and sea lions (Otariinae) is no longer correct.

However, this outdated division is still often used, as it is convenient to divide the sea lion family based on their external characteristics. Once a scientific consensus is reached, this article will be updated.

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Arctocephalinae

Northern fur seal (Callorhinus ursinus)
South American fur seal (Arctocephalus australis)
New Zealand fur seal (Arctocephalus forsteri)
Antarctic fur seal (Arctocephalus gazella)
Galápagos fur seal (Arctocephalus galapogoensis)
Juan Fernández fur seal (Arctocephalus philippi)
Cape fur seal (Arctocephalus pusillus)
Subantarctic fur seal (Arctocephalus tropicalis)

Otariinae

Steller sea lion (Eumetopias jubatus)
Australian seal ion (Neophoca cinerea)
South American sea lion (Otaria flavescens)
California seal ion (Zalophus californianus)
Galápagos sea lion (Zalophus wollebaeki)
New Zealand sea lion (Phocarctos hookeri)

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