Phocidea Family of True Seals

One True Seal of the Phocidea Family can be found in this website:

Pacific Harbor Seal, Phoca vitulina richardii. A representative of the Phocidae Family of True Seals.

Phylogeny: True Seals of the Phocidae Family are marine mammals. Like all mammals, they are in the phylum Chordata, the subphylum Vertebrata, the infraphylum Gnathostomata, the megaclass Tetrapoda, and the class Mammalia. They are in the subclass Theria of viviparous (live-bearing) mammals.  They are in the order Carnivora and are thought to be descendants of modern Bears. Phocids are in the suborder Caniforma and the infraorder Pinnipedia.  Pinnipeds include Walrus, True Seals and Eared Seals. The Phocidae Family is one of three families in this infraorder. The Phocidae Family contains fourteen genera and nineteen species. The name Phocidae comes from the Greek and Latin words meaning “seal” or “sea-dog”. Species in this family are also commonly called Earless Seals or Phocids.

Morphology: as pinnipeds, True Seals are large mammals, adapted to an aquatic life. The name Pinniped comes from the Latin for fin-footed, feather-footed, or wing-footed because the fore and hind limbs are shaped like fins or paddles. Their limb bones are long and enclosed within the spindle-shaped body. The torso skeletal structure allows for efficient swimming and still allows for land locomotion. They generally have relatively large eyes for improved vision in low light conditions, and whiskers for tactile sensation. All have a short tail. They have a blubber layer, and varying amounts of hair for warmth. True Seals differ from Eared Seals in that they lack an external ear flap. While they are sometimes called earless seals, this is a misnomer in that they do have internal ears. True Seals swim with their hind-flippers and use their fore-flippers to steer- just the opposite of Eared Seals. On land, they cannot walk on all fours, but drag themselves by pulling with their fore-flippers. This is an effective technique on ice, but less so on rock or sand. They have a thick blubber layer that can make up 25% of their body weight. Adults in the family have short, stiff hair, but also may be almost hairless; some species display spots or bands on their coats. The fore-flippers have well developed claws and are shorter than those of Eared Seals being less than 25% of the body length. The hind-flippers are longer than the fore-flippers and extend straight to the rear. The True Seals range in size from the Ringed Seal (90 kg, 200 lbs.) to the Southern Elephant Seal (3,600 kg, 7,920 lbs.).

Habitat and Distribution: True Seals may be found in open water well-offshore, nearshore, in the surf zone, or in bays. They may also be found on exposed rocky coastlines and sandy beaches. Some are found in rivers, and the Baikal Seal is found only in Lake Baikal in Russia. True Seals are accomplished divers, with the Southern Elephant Seal reaching depths of 2,390 m (7,835 feet). True Seals tend to be less social than Eared Seals. Like Eared Seals, they require access to land in order to breed and give birth, but overall, spend more of their time farther out to sea than Eared Seals. True Seals are found globally in every ocean except the Indian Ocean. Most species in this family are found in either Arctic or Antarctic waters with only a few species venturing into the tropics. Only the Northern Elephant Seal, Mirounga angustirostris, and the Pacific Harbor Seal, Phoca vitulina richardii, are found in Mexican waters.

Reproduction: As mammals, True Seals are gonochoric (male or female for life) and reproduce sexually with internal fertilization. True Seals may be polygynous, promiscuous, or monogamous. Gestation generally last 9-11 months, which usually includes a period of delayed implantation (embryonic diapause). Embryonic diapause is the blastocyst stopping developing for weeks or months, to ensure the pup is born at the most favorable time. The females give birth to one pup, which can swim within hours or days after birth. The lactation period is very short, ranging from 4 days to 6 weeks. Females generally reach sexual maturity between 3 and 7 years of age. Males usually take longer, with some species not breeding until 8-12 years of age.

Ecosystem Roles: True Seals prey on cephalopods, crustaceans, fish, penguins, macroplankton, and other seals. In turn they are preyed upon by sharks, Killer Whales, and other seals.