WHAT IS A MARINE MAMMAL Member of Class

WHAT IS A MARINE MAMMAL? • Member of Class: MAMMALIA • All possess major adaptations that allow them to live in the water (to a greater or lesser extent) • Some marine mammals live entirely in the marine environment, others may come on land for part of their lives • However, all marine mammals derive all (or most) of their food from the marine environment

POLAR BEAR Ursus maritimus

SEA OTTER Enhydra lutris

SIRENIANS - Manatees and dugongs

PINNIPEDS - Seals, sealions and walruses

CETACEANS Whales, dolphins and porpoises

PINNIPEDIA (Seals) CARNIVORA CANIDAE (Dogs) FELIDAE (Cats) PAENUNGULATA SIRENIA PROBOSCIDAE (Elephants) HYDRACOIDEA (Hyraxes) PERISSODACTYLA (Odd-toed ungulates) UNGULATA ARTIODACTYLA (Even-toed ungulates) CETACEA (Whales and dolphins) CRETACEOUS 65 PALAEOCENE 55 EOCENE OLIGOCENE 39

Whales, dolphins and porpoises are all members of the mammalian order CETACEA There are currently 84 (±) recognised species in the order.

Order: CETACEA Sub-Order: MYSTICETI The Baleen or “filter-feeding” Whales 10 or 13 species

• The Baleen whales all possess hundreds of plates of baleen instead of teeth. • Baleen is made of keratin and hangs from the upper jaw. • The fringed baleen plates trap engulfed prey and filter out water.

Order: CETACEA Sub-Order: ODONTOCETI The Toothed Whales 69 to 73 species recognised

The sub-order ODONTOCETI is split into ten families: Order Sub Orders Archaeoceti CETACEA Mysticeti Odontoceti Sperm whales Physeteridae Pygmy sperm whales Kogiidae Beaked whales Ziphioidea Indian river dolphins Platanistoidea Amazon river dolphin Iniidae Yangtze river dolphin Lipotidae Franciscana dolphin Pontoporiidae Beluga & Narwhal Monodontidae Dolphins Delphinidae Porpoises Phocoenidae

Cetaceans have adapted to a wide range of aquatic habitats RIVERS, LAKES, LAGOONS AND ESTUARIES: eg River, Irrawaddy and humpback dolphins INTERTIDAL (mudflats and mangroves): eg bottlenose & humpback dolphins SUBLITTORAL (continental shelf) – c. 45 miles from coast <200 m deep BATHYAL ZONE (continental slope) to 3, 500’ (1, 100 m): eg beaked whales ABYSSAL ZONE – flat and low productivity av. 13, 000’ (4, 000 m): eg sperm whale and beaked whale

Cetaceans have adapted to a wide range of aquatic habitats • TEMPERATURE: 40 o. C – humpback dolphins in the Arabian Gulf -1. 9 o. C – cetaceans in Antarctic • DEPTH: <5 m – river dolphins 2, 000 m – sperm whales 200 x atmospheric pressure

TEMPERATURE ADAPTATIONS COLD TEMPERATURES • Insulating blubber layer • Counter-current system reduced heat loss through flukes and fins as blood flows from body gives heat to cooler, parallel blood vessel entering body HOT TEMPERATURES • Vasodilation (blushing) • Increased blood vessels in skin

SWIMMING ADAPTATIONS • • Closable blowhole on top of head Fore limbs → flippers No hind limbs (or minute vestiges) No zygapophyses → back bone flexible Cartilaginous flukes Thick cornea & thick eye mucus Hydrodynamic (reduced drag)

HYDRODYNAMIC • • • Low Surface Area: Volume ratio No hair (facial bristles on some young) Skin replaced every 2 hours (keeps smooth surface) Genitals and gonads internal Blubber smoothes contours (tapered shape) Shape indicates speed: – Spinner dolphin: long beak (concorde) – Risso’s dolphin: blunt head (jumbo jet) – Sperm whale: square head (submarine)

BOUYANCY CONTROL • • • Buoyant blubber layer Flippers act as hydroplanes (produce lift) Porous bones Fat filled bones (eg mysticeti vertebrae) Dense bones (eg rib cages) Spermaceti organ – Waxy spermaceti changes density with temperature - adjustable buoyancy

DIVING ADAPTATIONS • High level of myoglobin (O 2 storage) • Blood diverted to essential organs • Retae mirabila: extra circulatory system → greater blood volume • High anaerobic tolerance in tissues • Blood storage in spleen – released in dives • Reduced blood viscosity • Bradycardia (25% in bottlenose dolphins) and decreased metabolic rate

DIVING ADAPTATIONS • Brain and heart most vulnerable to lack of oxygen • Cetacean brains operate at O 2 concentrations where a human would be unconscious • High levels of anaerobic respiration in brain at end of dive • Heart activity decreases (& O 2 demand) • Blood flow fluctuates (high/none) to periodically flush out anaerobic by-products • High levels of anaerobic respiration

AVOIDING THE BENDS • ‘The Bends’ are caused by dissolved nitrogen being absorbed into the blood stream under high pressure. • When pressure decreased the dissolved nitrogen come out of solution as tiny bubbles. • These bubbles can block blood capillaries – causes pain, paralysis etc.

AVOIDING THE BENDS • Rib cage collapsible & lungs can compress. • Air squeezed out of lungs and thorax into windpipe. • Windpipe thickened, does not absorb air (or dissolved nitrogen). • Rapid transfer of nitrogen from blood into lungs • Some absorption of nitrogen in mucus • Reduced circulation of blood to muscles – less risk or capillary block

OSMOREGULATORY ADAPTATIONS • High in take of salt • Saline surroundings (high OP) absorbs water from cetaceans • Specialised globular kidney (reniculi) looks like bunch of grapes • • High surface area for filtration Water produced by fat metabolism Seawater desalinated by kidney Very concentrated urine

SLEEP • Voluntary breathing – must be conscious to open blow hole. • A few species sleep as such: – Right whales (very buoyant) – Sperm whales (float – do not have to breathe for hours at a time) • Duplication of brain function – part of brain can sleep while another part awake.

HEARING • Odontocete vocalisations produced in windpipe • Focussed by fatty melon (acts like a lens) • In water sound would reach dolphin ears simultaneously – would not be able to pinpoint direction. • Sound received through lower jaw. • Two halves of lower jaw separated by insulating tissue. • Sound travels through jaw and vibrations passed to inner ear.

MIGRATIONS • Many large whale species migrate from polar region (to feed) to tropics (to breed) • Accumulation of stored fat before start • Vast distances – up to 50% weight loss • High speed: blue and fin whales 17 kmph for 3, 700 km. Why?

MIGRATIONS • Breed in warm waters as weather calmer for calves. • Calves loose heat easily as have a high surface area: volume ratio BUT – half of humpbacks, belugas, bowheads, orcas and narwhals never migrate (always polar) • Escape predators (killer whales) – although in tropics other predators (sharks) • Possible behavioural relic from when breeding and mating grounds closer unlikely

REPRODUCTION • Seawater is a spermicide – water tight valves • Prehensile penises • Some polygynous (eg orca, dominant male) • Almost all cetaceans promiscuous (multimate polygynandry) • Male competition -aggression (eg humpback - fin slapping) -vocalisations (eg humpback song – territories) -sperm competition (on average testes 25 x larger than expected - dusky dolphins testes relatively 100 x larger than humans)

REPRODUCTION • Most species sexually mature after 5 -6 years • However, may be denied mating by more dominant animals for several years • Always single calves are born • Some species have calving seasons, some species give birth year round • Usually 2 -3 year calving interval • Low reproductive rate

REPRODUCTION • Calves are born in water and pushed to surface. • Stay with mothers for six months to 10 years or more • Lactation via retractable nipples • Milk has very high fat content (40% only 4% in cow milk) • Calves may suckle for several years even after weaning (- bonding) • Females go through menapause

LONGEVITY • Harbour porpoise – 15 years • Bottlenose dolphin – 50 years • Killer whale – 90+ years • But only 20 -25 years in captivity • Blue whales - 100+ years • Bowhead whales – 218 years + Long life cycles and low reproductive rate means that the recovery of depleted populations is slow

West African manatee Similar to W. Indian manatee but: blunter snout more protruding eyes more slender body West Indian manatee

Dugong Tusks Cetacean-like tail No nails on flippers Totally marine Amazonian Manatee <3 m long White patches Totally freshwater

SIRENIAN ADAPTATIONS Ø All sirenians are totally aquatic - like cetaceans but unlike otters & pinnipeds Ø Herbivorous - unique amongst marine mammals Ø Various adaptations to aquatic environment

AQUATIC ADAPTATIONS • • • No pelvic limbs Reduced/paddle-like pectoral fins Fusiform (streamlined/spindle-shaped) body Very large - reduced heat loss Thick impermeable skin - reduced water loss Lobular kidney - improved water extraction/salt excretion • Nostrils on top of muzzle • Thick heavy bones (pachyosteosclerotic) – ballast • Lungs dorsal with two horizontal diaphragms – buoyancy control

MANTEE ECOLOGY • Nutritionally poor diet • Metabolic rate 20 -30 % lower than expected • Primarily plant diet -some times eat fish captured in nets & tunicates • Predation low: crocodiles/alligators and sharks • Most mortality: cold red tides boat collision by-catch

Pinniped = pinna (wing) + ped (foot) Comprise 25% of the 115 marine mammal species More than 50 million pinnipeds worldwide

Order: PINNIPEDIA Family: OTARRIDAE Eared seals Fur seals (9 species) Sealions (5 species)

Otarrids all have certain characteristics in common Visible external ears Hinged hind flippers Used fore flippers like wings – flying through the water = mobility on land

Order: PINNIPEDIA Family: OBENIDAE Walruses 1 species

Order: PINNIPEDIA Family: PHOCIDAE True seals Northern seals (Phocinae) 10 species Southern seals (Monachinae) 9 species

Phocids also have certain characteristics in common No external ears Use hind flippers for propulsion (side to side) Fore flippers used to direct Hind flippers not hinged = less mobility on land

Although they feed in the sea all seals give birth on land They “haul up” onto beaches to breed Seal pups are very vulnerable so they grow and are weaned quickly Seal milk is 30 -60% fat (vs 4% in cow milk) Pups gain weight & a thick blubber layer quickly

AQUATIC ADAPTATIONS • Webbed toes and fore limbs have developed into paddle-like pectoral fins • Fusiform (streamlined/spindle-shaped) body • Thick blubber layer - reduced heat loss • Insulating hair layer (especially in fur seals) • Flippers enervated with blood vessels – radiate heat when on land to avoid overheating

AQUATIC ADAPTATIONS • Counter current system to prevent heat loss via limbs in water • Nostrils on top of muzzle • Sensory vibrissae (whiskers) help to detect movement in water • Reflecting layer or TEPETUM in eye- allows low light vision

DIVING ADAPTATIONS • Can store large amount of oxygen in blood and tissues • Can withstand high concentrations of lactic acid (product of anaerobic respiration) • Can reduce their heart rate (BRADYCARDIA) and metabolic rate – reduces rate oxygen is used up • Lungs collapse when they dive – no absorption of nitrogen under pressure – no “BENDS”