You are currently browsing the tag archive for the ‘seals’ tag.

Ribbon Seal (Histriophoca fasciata)

Ribbon Seal (Histriophoca fasciata)

Here is a beautiful marine mammal which is somewhat underappreciated. The ribbon seal (Histriophoca fasciata) is a gorgeous medium sized true seal (Phocidae) which lives in the Arctic edges of the North Pacific. Populations of the seal range from northern Alaska down the Aleutians and from the Kamchatka Peninsula down along the coast of Asia to the Koreas and the northern tip of Japan. The ribbon seal is the sole surviving member of its genus and it is notable for its lovely yet bizarre coat—the adult seals are black with undulating ribbons of white running around their entire bodies.

Ribbon Seal, Photo by Michael Cameron.

Ribbon Seal, Photo by Michael Cameron.

Ribbon seals dive deep into the pelagic depths to hunt their prey. The diving mammals live on pollacks, eelpouts, cod, and cephalopods which they hunt at depths of 200 meters. The seals themselves are preyed on by polar bears, orcas, and large sharks—including sleeper sharks—huge predators of the benthic depths.

Pacific Sleeper Shark (Somniosus pacificus)

Pacific Sleeper Shark (Somniosus pacificus)

The seals are approximately human size: both males and females grow to about 1.6 m (5.2 ft) long, and weigh 95 kg (210 pounds). In ideal circumstances they can live longer than 25 years. Ribbon seals reach sexual maturity somewhere between the ages of two and six (depending on gender, diet, and heredity). They give birth to adorable fluffy white/silver pups who nurse for only four weeks before being forcd to hunt on their own!

Ribbon Seal Pup

Ribbon Seal Pup

Ribbon seals were overhunted by humans for their fur, but they live in such remote regions that they have probably never been in real danger of extinction. Their real numbers of ribbon seal populations are somewhat unknown but are estimated to be around 250,000. I can’t find any information about why they have such remarkable coats, so I will go ahead and guess that it is because they are fashionable!

ribbonSeal

A Crabeater Seal on an Iceberg (photo by Rob Wilson)

A Crabeater Seal on an Iceberg (photo by Rob Wilson)

The crabeater seal (Lobodon carcinophagus) is a pale-colored seal which lives on the pack ice around Antarctica.   Adult crabeater seals have an average length of 2.3 meters (7 and-a-half feet) and weigh around 200 kg (440 pounds) however the largest male crabeater seals can weigh up to 300 kg (660 lb).  The seals’ mass alters considerably over the course of a season as they gorge themselves in preparation for lean times (or—in the case of mothers—for nursing).  Like other Antarctica seals, crabeater seals have slender bodies and long snouts.  They are gifted swimmers—a talent which allows them to escape their two main predators, killer whales and leopard seals.  They infrequently venture beyond the continental shelves of Antarctica (although very rarely one is spotted at New Zealand, Patagonia, or South Africa).  They hunt along the pack ice and travel far inland to give birth.   The seals give birth to one pup annually and they can live up to 40 years.

A Crabeater Seal (Lobodon carcinophagus)

A Crabeater Seal (Lobodon carcinophagus)

Crabeater seals can slither over land fairly well and they range farther onto continental Antarctica than any other indigenous mammal.  Crabeater seal carcasses have been found up to 100 kilometers from the coast. So crabeater seals have whole swaths Antarctica to themselves (well aside from big weird penguins, lichens, and Norwegian explorers).   Although they may theoretically eat a crab every now and then, the seals are misnamed.  Their main prey is Antarctic krill, which they eat in huge quantities (as an aside, Antarctic krill is believed to have the greatest biomass of any single species on Earth).  Although they do not have baleen like the great rorquals, crabeater seals have specialized krill-filtering cusps on their teeth which trap the krill and allow water to escape.  When krill are not available, the seals can also feed on fish and squid.

Crabeater Seal Teeth

Crabeater Seal Teeth

Perhaps the most remarkable thing about crabeater seals is their sheer numbers.  Other than humans (and our livestock) they are the most numerous large mammals on the planet.  Caribou and wildebeests exist in herds of hundreds of thousands, but the crabeater seal population numbers in the millions.  The full population of crabeater seals is unknown.  Estimates range from 7 million to 70 million.  Since they are pale colored seals darting between the crushing pack ice of an uninhabited continent we have a population estimate which is off by a factor of ten.  The fact that so few people have seen them might explain why they are still so successful.

A Crabeater Seal enjoys sunbathing on a southern beach.

A Crabeater Seal enjoys sunbathing on a southern beach.

Walrus (Odobenus rosmarus) in Nunavut,Canada (photo by Mark Carwardine)

Today we feature one of everyone’s favorite animals–the great toothwalkers of the northern oceans, the mighty walruses (Odobenus rosmarus).  Adult Pacific male walruses can weigh more than 2,000 kg (4,400 pounds) and grow to lengths exceeding 13 feet.  The huge pinnipeds live in vast colonies ringed around the Arctic Ocean.  Females separate themselves from the fractious males in order to protect their calves from the squabbling and dueling of the bulls.  The tusks (which can grow to 1 m (3 ft 3 in) in length) are also used by both genders to leverage their great weight out of the water—hence the name “toothwalker.” The word walrus comes from the Old Norse word “hrossvalr” which means horsewhale.

(photo by Max Smith)

The distinctive face of the walrus is a mass of large coarse bristles properly known as vibrissae.  Like the barbells of a catfish, these vibrissae are extremely sensitive tactile organs which help the walrus find shellfish on the dark and turbid ocean bottom.  Walruses are capable of diving deep to find the invertebrates they like to eat.  Scientists have recorded dives of 113 meters (371 feet) which lasted for about 25 minutes.  Once the walruses have located a food source to their liking, they dislodge their prey with jets of water and then suction up the creatures.  Apparently they are most partial to bivalve mollusks, snails, sea cucumbers, and crabs, but in extreme circumstances they can hunt large fish or even smaller seals.

Walruses can sleep in the water, their heads supported by an inflatable pouch which allows them to bob comfortably in the choppy near-freezing water.  Additionally they change color with the temperature—their surface skin can be pink, as blood rushes near to the surface when they are hot, or they can turn grey brown when cold.

Walrus colony. Source (U.S. Fish and Wildlife Service)

All pinnipeds, including walruses, are in the order Carnivora where they seem to most closely share a common ancestor with bears back in the Oligocene. Walruses are the only species in the only genus of the family Odobenidae.  Once the Odobenidae were a sprawling family with at least twenty species spread across three several subfamilies (the Imagotariinae, Dusignathinae and Odobeninae), but something went wrong and walruses are all that’s left of the saber-toothed seals.

Polar bear attacking walruses (from the BBC's series "Planet Earth")

Walruses’ only natural predators are polar bears and killer whales, but even the world’s largest land predator and the most formidable ocean predator find adult walruses intimidating.  Except in extraordinary circumstances the huge predators only hunt calves or weakened walruses. Predictably, humans are the walruses’ main problem.  In the 18th, 19th, and 20th century immense numbers of walruses were killed for blubber, skin, meat, and ivory.  Today this commercial exploitation has ended and worldwide populations have rebounded somewhat–though certain geographic areas remain depopulated.

Perhaps because they move ponderously on land and because their whiskers suggest comic uncles, some people underestimate walruses. I have been fortunate enough to see a young adult walrus in captivity (he was orphaned as a pup and would have died if not taken in by an aquarium) and it is a mistake to underestimate these animals.  The walrus (whose name was Ayveq) was as large as a midsized truck, yet he could move with shark-like speed but ballet-like grace in the water.  Bull walruses come into maturity at the age of 7, but they don’t usually get to mate with cows until they are 15 or so and have bested many competitors in savage sword duels with their tusks. Ayveq had access to a harem of walrus cows from a much younger age, and his comic attempts to understand himself and his relation to the females was a source of much surprised astonishment among aquarium-goers.  As a peripheral point, I neglected to mention that male walruses have a uniquely large baculum which can measure up to 63 cm (25 inches)—larger than that of any other land mammal.  The apparatus supported by this bone is similarly oversized.

A tame picture of Ayveq the Walrus (he liked to mush his face against the glass)

Ayveq could produce a remarkable series of shrieks, grunts, whistles, bellows—apparently communication is important in the teaming masses of walrus colonies. Whether drinking herring through a straw, mugging for a crowd, or using his back flippers to amuse himself, Ayveq was always remarkable. His death saddened me considerably and I could not write about walruses without mentioning his extravagant personality.  Knowing Ayveq also left me convinced that walruses might be perverts but they are also highly intelligent and gregarious beings.  This conviction is born out by the painstaking work of biologists and zoologists who are just beginning to recognize how complicated walrus society is.  It is no wonder, that so many poets, artists, and musicians have referenced the remarkable tusked creatures.

The Walrus and the Carpenter from Alice in Wonderland (Walt Disney)

Ye Olde Ferrebeekeeper Archives

September 2019
M T W T F S S
« Aug    
 1
2345678
9101112131415
16171819202122
23242526272829
30