Bewoners van de Waddenzee

Knowledge repository

In het Waddengebied leven heel veel verschillende planten en dieren. Hoeveel van deze soorten zou je kunnen opnoemen? Misschien kom je wel tot een stuk of 5 soorten, of zelfs meer! Maar wist je dat er wel 10.000 soorten in zee en op het land leven? De helft hiervan leeft (deels) in zee¹. Op deze pagina maak je kennis met een aantal van deze zeebewoners. 

See also

  • Kokmeeuw - Waddenzee

  • De wadpier leeft in de bodem van de zee

  • Brandganzen

  • De zeehond is de graadmeter van de zee

Planten van de zee

In zee leven allerlei soorten planten. Alleen zien ze er anders uit dan je misschien gewend bent van de landplanten 

Vaste planten in de Waddenzee 

Er bestaan planten die vastzitten aan de bodem van de zee. Zo heb je de bekende zeewieren, die je wel eens aangespoeld ziet op het strand. Een minder bekende plant is zeegras: dit is een plant die in de Waddenzee veel voorkwam, maar waar het sinds 1930 ontzettend slecht mee ging door onder andere de wierziekte en de bouw van de Afsluitdijk. Er wordt al jarenlang gewerkt aan een project om de zeegrasvelden te herstellen in de Waddenzee.²

Zeewier - Waddenzee

Zwevende platen in de Waddenzee

Daarnaast heb je piepkleine planten die in het water zweven. Kleine, maar zeer fijne plantjes: Fytoplankton. Microscopisch kleine planten die in zee zweven en die dus niet vastzitten aan de zeebodem. In totaal zweven ze met miljarden in alle oceanen. Fytoplankton staan aan het begin van de voedselketen in zee en ze zijn daarom onmisbaar. Niet alleen voor het leven in de zee. Fytoplankton maken voor meer dan de helft van het zuurstof aan op aarde!³ Dus ook voor jou zijn ze onmisbaar.

Plankton - zeevonk

Bodembewoners van de Waddenzee 

Op het eerste gezicht lijkt de bodem van de Waddenzee misschien levenloos. Maar niets is minder waar! Zowel in als op de bodem kun je vele bewoners vinden. 

In de bodem

Een van de belangrijkste dieren die in de bodem van de Waddenzee leven is de wadpier. Deze worm leeft in een u-vormige buis in de zeebodem. The wadpier eet fytoplankton op dat in de bodem zit and poept daarna schoon zand uit. Dat zijn de vele hoopjes die je op de zeebodem kan zien als het eb is.

Schone zandhoopjes van een wadpier in de zeebodem.

De wadpier heeft veel buren in de zeebodem. Zo zijn er verschillende schelpdieren die bescherming vinden in de grond. Denk aan kokkels, nonnetjes of de zwaardschede (zie onderstaande foto). Ze graven zich in de bodem, soms tot wel 30 centimeter diep! [4]  

Hoe komen ze dan aan eten? Dat doen ze met behulp van hun sifo’s. Dat zijn een soort slangetjes waarmee ze met de ene sifo water ‘inslikken’ en fytoplankton opeten, en met de andere sifon het water weer uit hun lichaam halen. 

Schelpdieren

Op de bodem

Zeesterren en krabben zijn voorbeelden van soorten die óp de bodem van de Waddenzee leven. Zeesterren klinken misschien erg tropisch, maar ze komen ook zeker in de Waddenzee voor. Zij eten bijvoorbeeld schelpdieren zoals oesters en mosselen us.  

Did you know...

Zeesterren op een hele bijzondere manier mossels eten? Met de vele zuignappen die aan de armen vastzitten trekt een zeester de schelp open, duwt zijn maag uit zijn lichaam, de schelp in en eet zo de mossel op. 

In de Waddenzee leven verschillende soorten krabben. Krabben zijn alleseters: ze eten zeewieren, plankton, wormen, kleine schelpdieren en garnalen. Ze eten ook (delen van) dode dieren op. Hun voorste poten zijn de grote scharen. Met deze scharen kunnen ze hun prooi te pakken krijgen, in kleine stukjes scheuren of een schelp kraken.

Een krab op het strand

Zwemmers

Er komen zo’n 140 soorten vissen voor in de Waddenzee. [5] Bekende vissoorten als kabeljauw en haring ken je waarschijnlijk wel. Maar ken je ook platvissen, zoals tong en schol? Zij leven op de bodem van de zee. Zij hebben een goede camouflage, zodat ze niet opvallen. Sommige vissen blijven hun hele leven lang in de Waddenzee, anderen gebruiken deze zee tijdelijk omdat ze op trektocht zijn of ze komen daar alleen voor als ze nog jong zijn. 

Did you know...

De Waddenzee ook een leefgebied is voor haaien? De gevlekte gladde haai en de ruwe haai zijn hier voorbeelden van.

Watch this video

In deze video zie je hoe wij in 2016 een gevlekte gladde haai hebben gered.

Wadvogels

Het Waddengebied is van onschatbare waarde voor miljoenen vogels. Veel vogels maken gebruik van de Waddenzee als:

  • pitstop tijdens hun trekvlucht 
  • broedgebied in de zomer 
  • overwinteringsgebied 
  • algemeen leefgebied

Did you know...

De Waddenzee door miljoenen vogels wordt bezocht? 

Waarom kiezen ze voor de Waddenzee om te eten, te rusten en om te broeden? Dat heeft te maken met het feit dat de Waddenzee een getijdengebied is. Tijdens laagwater is de Waddenzee een lopend buffet! Als het eb wordt stroomt het water uit de Waddenzee weg en ligt de zeebodem open en bloot. Met hun dunne lange snavel kunnen de wadvogels hun eten uit de bodem halen.  

Scholeksters hameren bijvoorbeeld met hun snavel de schelp open om die te eten. Zodra het weer vloed wordt kunnen de vogels rusten op hoogwatervluchtplaatsen (hvp’s), de plekken die dan nog droog blijven liggen.  

Onderzoek naar de Waddenzee

Zeeroofdieren

In de Waddenzee zwemmen drie soorten zeezoogdieren rond. Een daarvan is de bruinvis. De bruinvis is een kleine walvissoort die jaagt op vis. De andere twee kun je misschien al wel raden: de common and grey seal. Zij staan aan de top van de voedselketen in de Waddenzee. De zeehond is een vleeseter en hun dieet bestaat uit vissen, garnalen, inktvissen en krabben. Er zijn zelfs berichten bekend van volwassen grijze zeehonden die bruinvissen aanvallen [6] en soms zelfs jonge grijze en gewone zeehonden [7]. 

Zeehond onder water


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zadelrob

Harp seal

Knowledge repository

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

See also

  • 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

Knowledge repository

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

  • Longwormpatient

  • 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

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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 microCTScientific 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

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Pup roept

Sound of a seal

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

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 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?

Source:

  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)

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.

The physique of sea lions is somewhat similar to that of seals. They have a long body with a large chest. Sea lions are generally built a bit slimmer than seals, with a more pointed head. Sea lions' front legs are a lot longer than those of seals.

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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Walruses (Odobenidae)

Knowledge repository

A family close to seals (Phocidae) is the walrus family. In terms of behaviour and body shape, they are very similar to seals and sea lions. Yet many walruses have one very recognisable feature: their tusks. Read on to get to know walruses a little better.

See also

  • Walrus

  • Walrus op ijs

  • Walrus op sneeuw

Odobenidae

The family of walruses is also known in science as the Odobenidae . Like seals, walruses belong to the order Carnivora, the carnivorous mammals. This order also includes animals such as wolves, bears and lions.

Walruses are one of the three members of the Pinnipedia (pinnipeds). This group of mammals is special because they spend much of their lives in the water. Their front and hind legs have turned into fins after millions of years of evolution, allowing them to move very well in water. The other two members of this group are sea lions (Otariidae) and seals (Phocidae).

This family is a bit special because it only has one relative! It might be a bit confusing, but the only species in the walrus family (i.e. the Odobenidae) is the walrus (Odobenus rosmarus). All other species have unfortunately been extinct for a long time.

How do you recognize walruses?

Walruses, like other pinnipeds, have a large, rounded thorax. Their abdomen is relatively small, giving them a cone-shaped body. They have shorter front flippers than sea lions. Nevertheless, walruses can lean on these, allowing them to lift their head and thorax off the ground.

Walruses have a lot less fur than seals and sea lions. Adult males sometimes look as if they have no fur at all. To stay warm, walruses have a thick layer of blubber. It often looks like walruses have extremely many small rolls of fat, especially the adults.

The only species still alive today (Odobenus rosmarus) has very recognisable tusks protruding down from the upper jaw. Fossils of very old walrus species show that many of their extinct relatives also had tusks.

Walking and swimming

Walruses on land

Walruses, like sea lions, can fold their rear flippers forward. This allows sea lions to lift their entire body off the ground to walk. Walruses cannot do that: they are too heavy for that.

Walruses move over land by dragging themselves forward with their front flippers. In the process, they push off with their rear flippers. The belly does not come off the ground in the process, so it slides over the ground. On land, they are somewhat more clumsy than sea lions.

Walruses in water

The way walruses move in the water is very similar to how seals do. They use their rear flippers to gain speed, but do not hold them flat against each other. They paddle alternately with their rear flippers while moving the abdomen back and forth.

Happily together

Walruses are social animals. On land, they lie down together in very close groups to rest. They also like to swim in groups in the water. Outside the mating season, males and females will usually live separately from each other. Walruses are pregnant longer and take care of their pups a lot longer than seals and sea lions.

During the mating season, different groups of males and females come together in a large group. The males then fight each other for a piece of territory. These fights can be fierce.

Where do walruses live?

The only walrus species alive today is found around the Arctic. They need shallow water with a soft seabed to hunt well. Therefore, they usually do not go very far from the shore. Walruses often rest in groups on sandy or rocky shorelines, as well as on the ice.

Walruses also used to occur a lot further south. Archaeodobenus, a primordial walrus, lived around Japan about 6 million years ago. At the same time, species also lived around California, such as the Gomphotaria. It seems they all lived in the northern hemisphere, as did the only surviving species.


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True seals (Phocidae)

Knowledge repository

What is a seal? What do seals look like and do you know how seals differ from sea lions? How many species of seals are there and where do they live? On this page you will learn more about the seal family.

See also

  • Gewone zeehond - Moeder zoogt pup

  • Gewone zeehond in de Waddenzee

  • Seals

Phocidae

The group of animals that we call true seals are all members of the family Phocidae .

Pinnipedia (pinnipeds)

Seals are mammals that live in the ocean, also known as marine mammals. Together with the family of sea lions and the family of walruses they are placed in a special clade of marine mammals. This clade consists of so called pinnepeds (Pinnipedia).

Pinnipeds got their name from the shape of their flippers. These animals have very short flippers, but with very long fingers and toes. This makes it look as if they have fins.

Carnivora

Seals belong to the order of mammals that mostly eat meat: CarnivoraThis order also includes animals such as bears, lions, wolves, sea lions and walruses .

Did you know...

Seals do not spend all their life in the water? The land is where they rest, warm up, mate and birth their pups. That is why we call them semi-aquatic: spending a part of their lives on land and in the sea!

Seals are carnivores, which means that they must eat other living animals to survive. They often eat fish, crustaceans and shellfish. Some species can eat very small animals such as krill. Others hunt for even bigger prey such as birds and other mammals.

How do you recognise seals?

You can partially recognize seals by their special physique. They have a long body with a broad chest and a small lower body. This gives them a streamlined, cone-shaped body. Their flippers are very short and wide and they have five digits which are webbed. This makes them perfectly suited for aquatic life.

H3: How do seals differ from sea lions and walruses?

Sea lions and walruses have similar physiques and adaptations, so what makes seals stand out? First of all, seals’ hind flippers cannot be folded underneath their body to walk on. Sea lions and walruses are able do this, which it easier for them to "walk" on land.

Seals have to hobble on their bellies to move on land. The way in which seals move is also referred to as caterpillar-like motion.

Another difference between sea lions and seals are their ears. Sea lions have small external ear flaps. Seals don't have such visible ears, they have ear holes on the side of the head.

Did you know...

That most seal species are larger than sea lions and walruses? The largest seal is the southern elephant seal (Mirounga leonina). Male southern elephants can weigh up to two tons!

Like a duck takes to water

Seals are strong swimmers. They have to be, as seals spend a lot of time in the water. In general seals can stay underwater for a longer period of time than sea lions and walruses. To hunt for food, some seal species must be able to dive very deep.

A seal has a special way of swimming. To speed up, seals swim with their hind flippers by holding them flat against each other and moving them quickly side to side. You could compare this to how fish swim. Fish also whip their tail to the side to move through the water. The front flippers of seals are a lot smaller than the back flippers. They also don't use it to move forward, but to steer.  

Did you know...

The northern elephant seal (Mirounga angustirostrisis a champion in deep diving? They have reached depths as great as 1500 meters. In these depths they hunt for prey such as squid and other deep sea animals. Northern elephant seals can hold their breath for a very long time: almost 2 hours!

(A)social

Most seal species live a solitary lifestyle. This means that they prefer to do almost everything on their own. The only exception is during the mating season, because then the animals congregate in large numbers to birth pups and mate. When mating season is over, the seals moult together, after which they each go their separate ways.

You can see seals resting in groups on beaches and sandbars, but that does not mean that they like to be together. Because seals are less agile on land, they cannot run away from large predators. Therefore, when the seals are on land it is safer for them to be with other seals. Additionally, often times there is not enough space to lie far apart so they are “forced” to be closer than they would want to.

Where do seals live?

Seals can be found in every ocean of the world. They often live along the coasts or on the ice of the North or South Pole. There is even a species of seal that does not live in the sea, but in the freshwater Lake Baikal in Russia! Each species is adapted to live in certain areas and not one seal species can be found all over the world.

Did you know...

There are two seal species living in the Netherlands? The common seal (Phoca vitulina) and the grey seal (Halichoerus grypus).

How many seal species are there?

The true seal family (Phocidae) is often divided into two subfamilies: northern seals (Phocinae) and southern seals (Monachinae). The group of northern seals consists of ten species. The southern seal group is made up of eight species. Worldwide there are a total of eighteen different seal species.


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Northern hemisphere seal species

Bearded seal (Erignathus barbatus)
Hooded seal (Cystophora cristata)
Harp seal (Pagophilus groenlandicus)
Ribbon seal (Histriophoca fasciata)
Baikal seal (Pusa sibirica)
Ringed seal (Pusa hispida)
Caspian seal (Pusa caspica)
Largha seal (Phoca largha)
Common seal (Phoca vitulina)
Grey seal (Halichoerus grypus)

Southern hemisphere seal species

Leopard seal (Hydrurga leptonyx)
Weddell seal (Leptonychotes weddellii)
Crabeater seal (Lobodon carcinophaga)
Ross seal (Ommatophoca rossii)
Northern elephant seal (Mirounga angustirostris)
Southern elephant seal (Mirounga leonina)
Hawaiian monk seal (Neomonachus schauinslandi) Mediterranean monk seal (Monachus monachus)

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Carnivora

Knowledge repository

Seals belong to the order Carnivora. This is a special group of animals within the class Mammalia (mammals). Carnivora are mammals that are specialized in eating other animals, better known as carnivores.

See also

  • Zeeleeuw

  • Wasbeer

  • Sneeuwluipaard

Did you know...

When scientists study the evolution of certain species, it helps to divide them into categories. This categorization is called classification or taxonomy. For example, the scientific classification of the common seal (Phoca vitulina) is this:

Domain (Eukarya) -> Kingdom (Animalia) -> Phylum (Chordata) -> Class (Mammalia) -> Order (Carnivora) -> Family (Phocidae) -> Genus (Phoca) -> Species (Phoca vitulina)

Ancestors of the Carnivora

Millions of years ago, dinosaurs were the dominant animals on Earth. During that time there were mammals, but their fossil records showed that they were the size of tiny shrews. They specialized in living nocturnal lives, a feature that mammals still have to this day.

The first mammals ate insects in order to survive. After the massive extinction of the dinosaurs there was room for mammals to expand and evolve. This resulted in various mammals with all kinds of specializations. This gave rise to the specialization of eating meat; the birth of the order Carnivora.

Miacis Congitus

The oldest Carnivora fossils that have been found are from the Miacis congnitus. These predators somewhat resembled modern civets with their long, agile bodies and long tails. Miacis most likely lived in trees and ate small invertebrates, reptiles and birds. They lived during the late Paleocene and early Eocene epoch (62 – 34 million years ago). All modern Carnivora descend from these prehistoric animals, including seals.

Phocidae: the pinnipeds

Do you want to learn more about the evolution of the seal family? Check out our page on the evolutionary history of the Phocidae.

How do you recognize Carnivora?

They are mammals

All the Carnivora are mammals (Mammalia). This means that they nourish their offspring with milk.

They are viviparous

All Carnivora are 'viviparous’. This means that they develop their offspring in the placenta inside the uterus of their mother and give birth to "living” young.

Large skull

Carnivora have a relatively large skull with a large cranium. They have large brains and are considered to be intelligent animals. In general Carnivora have somewhat rounder heads than other mammals. These rounder heads ensure that their eyes are well positioned for hunting other animals.

Position of the eyes

The shape and position of their eyes are striking. Carnivora have relatively large eyes that are close together. Because both their eyes face forward, Carnivora such as seals have a very good depth perception. This is extremely important for carnivores. After all, in order to hunt other animals they must be able to see exactly how far away their prey is.

Sharp teeth

But the easiest way to recognize Carnivora is by their teeth. Because Carnivora eat meat, their teeth have been adapted to killing and eating animals. They have large, pointed canine teeth and sharp, serrated molars. This helps carnivores to cut muscles and tendons and even crack bones.

Zelfs zeehondenpups hebben al scherpe tanden

Foto: Martina Zilian

Did you know...

That Carnivora does not have the same meaning as carnivores?

Carnivora and carnivores

Thes two words can be confusing, because they seem very similar. They do not have the same definition.

The Carnivora are an order of mammals that are adapted to eating meat. To survive, they must kill animals or find carcasses. When talking about Carnivora we are talking about the classification of carnivores in relation to other mammals. Examples are wolves, lions and seals.

But these mammals are not the only animals that eat meat. If an animal's diet consists mainly of meat, we are talking about a carnivore diet. Birds of prey, crocodiles, Tyrannosaurus rex and seals are therefore all carnivores.

How can you live on meat alone?

To eat and digest high-fiber plants (such as grass) you need an extremely long and complex digestive system. This is because plants are very difficult to digest and that take a lot of time. They also have very few nutrients, therefore herbivores are almost constantly eating.

Meat, on the other hand, is easier to digest. Carnivora therefore have very short, simple digestive systems. Meat is also very rich in energy and protein, so they can spend less time eating compared to herbivores.

But depending on energy alone is not enough to survive. As you may know, animals also need vitamins, fats and minerals. Therefore, Carnivora not only eat the meat from their prey, but also their organs, fat, skin and sometimes even their bones. It contains all the nutrients an animal could wish for. Seals, for example, swallow many of their prey whole. Skeleton and everything else.

Did you know...

That the seal is the largest predator of the Netherlands?

Do Carnivora only eat meat?

Not always. There are species that eat almost exclusively meat, but there are also Carnivora with a mixed diet. Yet we still call them carnivores, because their bodies are mainly specialized in eating and digesting meat.

Hypercarnivores

If the diet of a Carnivora consists of at least 70 percent meat, we call them hypercarnivores. They cannot digest other foods properly or at all. Seals and the other Pinnipedia are hypercarnivores. They only eat meat, so no plant materials.

Hypocarnivores

There are also Carnivora with a mixed diet. If they consume meat for less than 30 percent of their diet, we call them hypocarnivores. They often eat mushrooms and fruit in addition to meat. These contain little fiber and a lot of sugars and proteins, so they are quite easy to digest for Carnivora. Brown bears (Ursus arctos) are known hypocarnivores. For their hibernation they have to build up a lot of reserves. That is the reason why they eat everything they come across.

Mesocarnivores

In between the hyper- and hypocarnivores you have so-called mesocarnivores. Their diet consists of 50-70 percent meat. Many canids are mesocarnivores. They mainly eat meat, but they can also digest certain plants as long as they don't contain too much fiber.

Did you know...

The giant panda (Ailuropoda melanoleuca) is a bear species from the order Carnivora that eats almost exclusively high-fiber bamboo? If you look closely at the teeth of a giant panda, you will see that the serrated molars are a lot flatter than those of other Carnivora. This helps the panda to crush these woody plants.

Families in the order Carnivora

Within the order Carnivora there are 16 families and 296 species. The families are divided into two suborders : the Caniformia and the Feliformia.

Caniformia

The suborder Caniformia consists of nine families:

Feliformia

The suborder Feliformia consists of seven families:

  • Felidae (felines)
  • Eupleridae (Madagascarian carnivorians)
  • Herpestidae (mongooses)
  • Hyaenidae (hyenas)
  • Nandiniidae (African palm civets)
  • Prionodontidae (Asiatic linsangs)
  • Viverridae (civets and genets)

Did you know...

That the largest species within the order of Carnivora is the southern elephant seal (Mirounga leonina)? These seals can be more than 6 meters long and weigh 3,700 kilos!


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