Marine Mammals – Diversity

General Characteristics of Mammals Nurse young with mammary glands Insulation to maintain endothermy (hair, blubber) All marine forms with internal development (via

placenta) All marine forms evolved from terrestrial ancestors

Diversity of Marine MammalsOrder Cetacea: whales, dolphins, and porpoises

Suborder Odontoceti (toothed whales): echolocation and teeth Suborder Mysticeti (baleen whales): strain food with baleen

Order Pinnipedia: true seals, eared seals, and walrusOrder Sirenia (sea cows): manatees and dugongOrder Carnivora: sea otter (insulation with dense fur) and

polar bear

Marine Mammals – Cetaceans Baleen Whales (Mysticeti): baleen (whalebone)

composed of keratin, filters plankton and small fishes Rorquals: with pleated, expandable throats; include Blue,

Finback, Humpback, Sei, Bryde’s, and Minke Whales Blue Whale: largest animal, with low-frequency calls Humpback Whale: long, white pectoral flippers; males sing Minke Whale: currently hunted (ex., Japanese “scientific

whaling”) Right Whales: first to be hunted (slow, float when dead)

Southern Right Whale: males with oversized testes (sperm competition; females with multiple partners)

Northern Right Whale: critically endangered (migratory routes in shipping lanes)

Bowhead: Arctic; over-hunting led to calls for protection in 1800s

Gray Whale: migration from Bering Sea (feeding) to Baja (mating and calving in lagoons); western population extinct (?)

Figure 5-105

Marine Mammals – Cetaceans Toothed Whales (Odontoceti): lack baleen; teeth present

Sperm Whales (incl. pygmy and dwarf sperm whales) Males with larger head, filled with spermaceti wax (clean burning and fine

lubricant); dives to 4000 meters (90 min) to hunt giant squid; ambergris (digestive fluid) perfumes; “Moby Dick” whale

Beaked Whales: oceanic, deep divers, uncommon to rare (several species); males often with tusks (used aggressively)

Arctic Whales – Narwal: male with long single tusk, and Beluga: white whale, found in large pods; sing

Dolphins - include killer whale (note resident orcas of Pacific North-west), bottlenose (coastal), common (offshore),

spinner and spotted (tropical), pilot whales (mass strandings), and river dolphins: boutu (Amazon), susu (India), beiji (China, likely extinct due to habitat loss re. Three Gorges Dam)

Porpoises: spade-like teeth, lack snout; include harbor porpoise, Dall’s porpoise, and vaquita (smallest cetacean; Gulf of California; endangered)

Figure 5-108

Marine Mammals - Cetaceans Fully aquatic: horizontal tail fluke, blowhole, vestigial hind limbs

Extensive fossil record with intermediate forms (re. loss of hind limbs and evolution of blowhole)

Large-scale migrations common between feeding and calving groundsEndothermic: blubber (thick layer of subcutaneous fat); counter-

current heat exchange and rete mirabile (“beautiful net”) Diving: lungs collapse before dive (reduces nitrogen/bends);

dive reflex (blood shunted to core) and bradycardia (heart rate slows); blowhole under voluntary control; efficient gas

exchange (muscles with myoglobin)Intelligence and Communication: easily trained (entertainment

and research); cooperative hunting and birthing documented in the wild; social groups with shifting relationships; communication via signature whistles (dolphins), songs of humpbacks and low- frequency moans of other baleen whales; echolocation for detection and tracking of prey, sensing surroundings

Figures 7-30 and 7-31

Marine Mammals - Pinnipeds Most with polygynous mating systems (harems with rookeries)True Seals (Family Phocidae): no external ears, swim with rear

flippers, crawl on belliesNorthern Elephant Seal: dives to 1250 m; males with proboscis

and large canine teeth; population bottleneck in recent pastHawaiian Monk Seal: critically endangered; preyed on by sharksOthers: harbor seals; ringed and harp seals (Arctic); Weddell,

crab- eater, leopard seals (Antarctic)Eared Seals (Family Otaridae): external ears, swim with front

flippers, walk with hind flippersCalifornia Sea Lion: protected by Marine Mammal Act;

overpopulated?Stellar Sea Lion: North Pacific; population declines due to fish lossFur Seals: Northern, Galapagos fur seals

Walrus: lack external ears, but walk on hind flippers; males with twin tusks; Arctic habitat

Figures 5-104b and 15-18

Marine Mammals - Others Order Sirenia (sea cows): large, flat tails; eat surfgrasses; all

endangered due to over-hunting; mermaid legendsManatee: Florida and Caribbean; swim up rivers; often hit by boatsDugongs: Indo-Pacific; marine (coastal wetlands and mangroves)Stellar Sea Cow: extinct by 1768; fed on kelps; over-hunted by whalers

Order Carnivora: defined by carnassial tooth (shears flesh)Sea Otter: Alaska south to Central California; use rock tools to open

shellfish; insulated by coat of fine hairs (lack blubber); must eat 25% of body weight per day; very social

Polar Bear: truly marine due to adaptations (webbed feet, transparent eyelids); Arctic habitat; declared threatened (re. declining time periods between seal pup births and ice breakup)

The Aquatic Ape Theory (Hardy, 1960): humans adapted for aquatic life and possessed an aquatic ancestor; supported by anecdotal evidence (hairlessness, breath control, oil glands)

Figure 5-109

Marine Mammals – Modern Whaling International Whaling Commission (IWC): formed in 1946 in

response to the near extinction of large whales (to manage the fishery; voluntary membership, no enforcement)Banned whaling in 1982 (took effect in 1986); Japan signed

with allowance to kill 500-600 Minke whales a year; Norway once a member but later withdrew, continued hunting Minke whales

Established Southern Ocean Whale Sanctuary in 1994 Island nations in Caribbean receiving millions of dollars in aid

from Japan and joining IWC as pro-whaling nationsMarine Mammal Protection Act (U.S., 1972): protects all

marine mammals from direct hunting in U.S. waters; preceded U.S. Endangered Species Act (1973)

Explosive harpoons replaced with electrocution and thermal harpoons (5000⁰ instant combustion snaps spine)