Marine Mammals – Diversity

1. 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 Mammals • Order 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 walrus • Order Sirenia (sea cows): manatees and dugong • Order Carnivora: sea otter (insulation with dense fur) and polar bear

2. 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 (?)

3. Figure 5-105

4. 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)

5. Figure 5-108

6. 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 grounds • Endothermic: blubber (thick layer of subcutaneous fat); counter- current heat exchange and rete mirabile (“beautiful net”) • Diving: lungs collapse before dive (reduces nitrogen/bends); divereflex (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

7. Figures 7-30 and 7-31

8. Marine Mammals - Pinnipeds • Most with polygynous mating systems (harems with rookeries) • True Seals (Family Phocidae): no external ears, swim with rear flippers, crawl on bellies • Northern Elephant Seal: dives to 1250 m; males with proboscis and large canine teeth; population bottleneck in recent past • Hawaiian Monk Seal: critically endangered; preyed on by sharks • Others: 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 flippers • California Sea Lion: protected by Marine Mammal Act; overpopulated? • Stellar Sea Lion: North Pacific; population declines due to fish loss • Fur Seals: Northern, Galapagos fur seals • Walrus: lack external ears, but walk on hind flippers; males with twin tusks; Arctic habitat

9. Figures 5-104b and 15-18

10. Marine Mammals - Others • Order Sirenia (sea cows): large, flat tails; eat surfgrasses; all endangered due to over-hunting; mermaid legends • Manatee: Florida and Caribbean; swim up rivers; often hit by boats • Dugongs: 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)

11. Figure 5-109

12. 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 nations • Marine 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)