Marine Mammals—Cetaceans and Sirenians

Lecture 9

Marine Mammals—Cetacean origins • Share a common ancestor with the modern

hippopotamus

Pakicetus> 50 mya—whale-like skullMainly terrestrial, foraged in freshwater

Ambulocetus< 50 mya—vertebrae suggest undulation swimming

Coastal species—still bred on land

Marine Mammals—Cetacean origins

Dorudontids< 40 mya— over 15 feet long

Dorsal nasal openings; tail flukeToes still evident; vestigial hind-legs

Protocetids—a diverse group45-35 myaLarger global distribution—open waterLarge nasal openings—higher on head; eyes lower

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

Cetacean Characteristics• Well developed tail—undulations dorsoventral– Why dorsoventral?

• Vestigial hind limbs• Hair eliminated—streamlining

• Nostrils top of head—blowhole – No pharynx– Most odontocetes have lost smell

• Blubber—insulation, buoyancy, energy storage– Up to 1 foot thick– Capillaries constrictable

Cetacean Characteristics

Blubber• Historically, whales hunted for blubber– Food, lamp oil, soap, margarine, cosmetics, candles

• Harpoon tip (1880) in bowhead whale

Echolocation• Natural SONAR system– Odontocetes

• Sounds (clicks, whistles) produced—phonic lips

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

Echolocation—Sperm Whales

https://www.youtube.com/watch?v=W_PuO7gzfqI

Cetacean Hearing• Inner ear outside skull– External ear canal vestigial

• Acoustic fats—channel sound toward inner ear– Amplified

Minke Whale

Dolphin

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

Humpback vocalizationsWhalesong—males on breeding grounds repeat

5-20 minute-long “song”– Projects > 20 miles

• Song is population-specific– Evolves over time

Bubble-net feeding

Mysticete FeedingBaleen—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

Mysticete Feeding—Family Balaenidae

Right Whale

Mysticete Feeding

Rorqual WhalesPleats

Gray whale

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

Odontocete hunting

Strand feeding

Odontocete hunting

Mud-ring feeding prey-specific strategy

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—

Cetacean divingOxygen 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’

• Breath holding at surface—• Heart rate slows when diving– Blood flow to extremities and guts restricted

• Lungs collapsible, air nonrespiratory areas– Rib cage flexible

Cetacean diving

• Counter-current heat exchange in tongue

Artery

Veins

MigrationMore common among

mysticetes– Breeding/calving areas

in tropical latitudes– Feeding in temperate

or polar regions

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

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

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

Manatee Characteristics

Vestigial hind limbs

Dorsal placednostrilsNails on flippers

Manatee Characteristics

Tactile sensorywhiskers

Small brains

Manipulative lipshttps://www.youtube.com/watch?v=6c6yYq1wjOU

Manatee Characteristics• Osmoregulation–Need to drink freshwater• Freshwater springs

– Effective kidneys• Diving physiology– Large dorsal lungs– Short dive duration• < 20 min

• 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

Manatee Characteristics—feeding

Marching molars

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

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