72 10.6 Marine Mammals: Seals, Sea Lions, Walruses, Sea Otters, and Manatees
Suborder Pinnipedia: seals, sea lions and walruses
- As a group, they are fairly young, having been around for only about 25 million years
- They consist of three families:
- Otariidae: sea lions
- Phocidae: true seals
- Odobenidae: walruses
Otariidae (sea lions) have:
- small, but obvious external ears
- long, flexible necks
- independent and mobile hind limbs that permit substantial movement on land
- nostrils that are located at the tip of the snout
- a dense and soft undercoat of fur protected by a layer of long and close guard hairs
- several layers of blubber for thermal protection
Phocidae (true seals) differ from sea lions in that they have:
- no external ears
- smooth, coarse hair with no underfur
- a hind limb geometry that restricts their ability to move on land
- fore flippers that are smaller than those of sea lions
Diving behavior and adaptations:
- can shut off their nostrils completely while diving
- can restrict the flow of blood to vital organs
- can store lots of oxygen
- routinely dive for 30 minutes
Odobenidae (Walruses):
- These creatures are limited to the Arctic waters of the Atlantic and Pacific
- Their hind limbs are similar to those of sea lions, but they have no external ear
- The most characteristic feature is the set of enlarged canine teeth – tusks
- They may weigh up to 4000 pounds
- They have air sacs in their cheeks that are used for support like a life preserver because they sleep in the water
- They also use their tusks to hoist themselves out of the water onto the ice
- They are becoming rare; estimates of their numbers world-wide are around 170,000 to 190,000 individuals
Suborder Fissipedia: sea otters
- These members of the weasel family are included in the list of marine mammals because they do live in the sea and are obviously mammals
- They have the distinction of having the most valuable fur of any animal – their dark brown underfur is extraordinarily dense and rich
- Trade in sea otter fur dates back at least to 1786, under the Spanish
- This became the most important industry of the California coast and most otters were gone by 1850
- In 1900, a small population was discovered near Bixby Creek on the central California coast
- Today, the otter’s range has expanded along much of the Pacific coast of the U.S., especially since their protection under the Marine Mammal Protection Act of 1972
- They grow to lengths of about 5 ft and weights up to about 80 pounds
- They live for up to about 20 years
- They live by foraging for urchins, abalone, mussels, clams, crabs and other tidbits in relatively shallow water, rarely diving deeper than 60 ft
- They frequently consume their food in an attitude of leisure as they float gently on their backs
- They will use stones to smash open shellfish by placing them on their stomachs as they float on their backs
- They have very high metabolic rates and must consume up to 25% of their body weight each day in order to maintain an internal temperature of 100 degrees
- This works out to be about 140 to 190 calories per kilogram of body weight per day, compared to the average human who must consume about 32 calories per kilogram of body weight per day
- If a sea otter doesn’t eat for a day, it will lose up to 10% of its body weight
- They live in the kelp forests and use the kelp as a tether while resting at the surface
- They help protect the kelp forest by eating the sea urchins that feed on the kelp
- They also use the kelp as protection from their enemies, including sharks and killer whales
- Making them a keystone species in this habitat
Order Sirenia: Sea Cows
- This group includes the manatees, which are found in the shallow bays and estuaries of North America and Africa, and the dugongs, which are found in the Indo-Pacific regions
- They’re common in the winter in the warm-springs of Florida’s west coast including the Crystal River
- These lovable rascals feed on water plants (especially the hyacinths in southern canals) – they’re strictly vegetarians
- They show little fear of man and, as a result, many are killed or severely injured each year by boat propellers, as they have a habit of swimming just below the surface
- They form family groups and appear to show great care and affection for family members
The Sirenians were named after the Sirens, the mermaids that Ulysses encountered on his return from the Trojan wars – apparently they resembled mermaids to sailors who had been too long at sea or were drunk (or maybe both)…
Dr. Cristina Cardona