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Marine Mammals—Cetaceans and Sirenians

Marine Mammals—Cetaceans and Sirenians. Lecture 9. Marine Mammals—Cetacean origins . Share a common ancestor with the modern hippopotamus. Pakicetus > 50 mya —whale-like skull Mainly terrestrial, foraged in freshwater. Ambulocetus < 50 mya —vertebrae suggest undulation swimming.

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Marine Mammals—Cetaceans and Sirenians

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  1. Marine Mammals—Cetaceans and Sirenians Lecture 9

  2. Marine Mammals—Cetacean origins • Share a common ancestor with the modern hippopotamus Pakicetus > 50 mya—whale-like skull Mainly terrestrial, foraged in freshwater Ambulocetus < 50 mya—vertebrae suggest undulation swimming Coastal species—still bred on land

  3. Marine Mammals—Cetacean origins Protocetids—a diverse group 45-35 mya Larger global distribution—open water Large nasal openings—higher on head; eyes lower Dorudontids < 40 mya— over 15 feet long Dorsal nasal openings; tail fluke Toes still evident; vestigial hind-legs

  4. Order Cetacea • Two major groups of cetaceans • Mysticeti—baleen whales • 15 species • Odontoceti—toothed whales (and dolphins) • 75 species—5 freshwater • Possess all mammal characteristics— • ____________ evolution  more fish like

  5. Cetacean Characteristics • Well developed tail—undulations dorsoventral • Why dorsoventral? • Vestigial hind limbs • Hair eliminated—streamlining

  6. Cetacean Characteristics • Nostrils  top of head—blowhole • No pharynx • Most odontoceteshave lost smell • Blubber—insulation, buoyancy, energy storage • Up to 1 foot thick • Capillaries constrictable

  7. Blubber • Historically, whales hunted for blubber • Food, lamp oil, soap, margarine, cosmetics, candles • Harpoon tip (1880) in bowhead whale

  8. Echolocation • Natural SONAR system • Odontocetes • Sounds (clicks, whistles) produced—phonic lips

  9. Echolocation • Odontocetes vary frequency and duration of clicks • Can produce > 1000 per second • Frequency often too high for humans • Higher frequency  short range & small prey • Differences in echo timing  density differences • Solid structures • Fish buried in sand http://swfsc.noaa.gov/textblock.aspx?Division=PRD&ParentMenuId=148&id=5776 Melon acts as a lens—direction and width of sonic signals can be modified

  10. Echolocation—Sperm Whales https://www.youtube.com/watch?v=W_PuO7gzfqI

  11. Minke Whale Cetacean Hearing • Inner ear outside skull • External ear canal vestigial • Acoustic fats—channel sound toward inner ear • Amplified Dolphin

  12. Mysticete sound production • Lack phonic lips and melon • No echolocation • Boat collisions • Sound produced with larynx • Supported by cartilage and muscles • Tissue folds vibrate—resonation chamber • Air recycled • Variable among species http://whalewatch.com/research/sounds.php

  13. Humpback vocalizations Whalesong—males on breeding grounds repeat 5-20 minute-long “song” • Projects > 20 miles • Song is population-specific • Evolves over time Bubble-net feeding

  14. Mysticete Feeding Baleen—fibrous-keratin plates hang from upper jaw • Inner surface bristled • Evolved 25 to 30 mya • Embryonic mysticetes have teeth precursors • Tongue removes strained prey • Largest animals in history

  15. Mysticete Feeding—Family Balaenidae Right Whale

  16. Mysticete Feeding Gray whale Rorqual Whales Pleats

  17. Odontocete hunting • Coordinated group hunting common • Population & individual-specific hunting tactics • Learned behavior & innovation • Foraging specialists— • Reduces competition • Pacific & Antarctic Killer whales • Dolphins in Florida Bay • Common odontocete hunting tactics • Chasing, herding, echolocating buried prey, stealing from fisherman

  18. Odontocete hunting Strand feeding

  19. Odontocete hunting Mud-ring feeding prey-specific strategy

  20. Osmoregulation • Poorly understood compared to other vertebrates • Water gained from prey • Well developed kidneys • Seawater is not ingested • Unless fasting • Concentrated urine eliminates salt • Respiration loss minimized  efficient O2 extraction • Metabolic water—

  21. Cetacean diving Oxygen storage ability • Some species have large lungs • Large tidal volume—highest among vertebrates • Large airways  • High blood volume • concentration of RBCs • RBCs with hemoglobin • Muscles myoglobin • Narwhal ½ O2 in muscles Up to 40’

  22. Cetacean diving • Breath holding at surface— • Heart rate slows when diving • Blood flow to extremities and guts restricted • Lungs collapsible, air  nonrespiratory areas • Rib cage flexible Artery • Counter-current heat exchange in tongue Veins

  23. Migration More common among mysticetes • Breeding/calving areas in tropical latitudes • Feeding in temperate or polar regions

  24. Reproduction • Poorly documented in most species • Internal fertilization • Internal—protrusible penis • 10 feet long in blue whale • Males aggressive with eachother • Courtship displays common • Fat-rich milk • Blue whale calf  up to 200 lbs. per day

  25. Reproduction—vulnerable life-history • Age at maturity variable—average 10 years • Males later for some species • One calf • Gestation 10 - 12 months • Timed with migration for mysticetes • Breed every other year at most • Some species females  5 year interval • 1+ years of infant care • Life-span variable • 40 to 130+ years

  26. The Mighty Manatees • Order Sirenia(dugongs & manatees) shares common ancestry with elephants • 1rst appear 50 mya • Peak diversity ~20 mya • Only herbivorous fully aquatic mammals in history • Two genera • 3 sp. manatee • 1 sp. dugong

  27. Manatee Characteristics Dorsal placed nostrils Nails on flippers Vestigial hind limbs

  28. Manatee Characteristics Small brains Manipulative lips https://www.youtube.com/watch?v=6c6yYq1wjOU Tactile sensory whiskers

  29. Manatee Characteristics • Osmoregulation • Need to drink freshwater • Freshwater springs • Effective kidneys • Diving physiology • Large dorsal lungs • Short dive duration • < 20 min

  30. Manatee Characteristics—feeding • High food intake—5-7% of body wt. per day • Aquatic plants—non algae • May consume animals—tunicates, entangled fish • ~60’ of intestines • Gut microbes • Tooth replacement throughout life • Slow metabolism Marching molars

  31. Florida Manatee • The largest Sirenian • > 3000 lbs, 12 feet • Restricted to Florida during winter • Freshwater springs • Migrate as far north as Virginia in summer • Possess layers of blubber • Less developed than cetaceans

  32. Manatee Threats • Slow population growth • 1 calf per female every 2-3 years • Hunted for meat • Presently very rare in Florida • Habitat loss/deterioration • Fishing gear interactions • Boat strikes—25% of FL mortality • Florida Manatee ~5000 individuals • Endangered

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