Marine Mammals

Phylogeny of Marine Mammals

Four groups of marine mammals are separate evolutionary lines – each entering the marine environment independently

Whales share a common ancestor with even-toed ungulates (cattle)

Sirenians share a common ancestor with the Proboscidea (elephants)

Otters are a separate evolutionary line from the walruses, seals and sea lions – all of which share a common ancestor with other carnivores

Whales

Sirenians

Sea

Otters

Pinnipeds

Marine mammals,

birds,and reptiles are

all classified in the

Phylum Chordata,

Subphylum Vertebrata.

Know the Class and

Order associated with

each of the groups of

marine mammals.

Order Cetacea – The Whales

The Whales Group of mammals which includes whales, dolphins,

and porpoises

Natural selection forces have produced convergent evolution for the cetaceans – stream-lined body form

Cetaceans’ front flippers have the same bone structure found in other mammals

Cetaceans have reduced pelvic girdle

1. lost hind limbs as adults

2. hind limbs are present in the embryonic stage

Natural selection on different marine organisms has produced an

efficient, streamlined body form with counter shading in three

separate evolutionary lines. This is called convergent evolution.

Fetus of a white-sided

dolphin. Two pairs of

limbs are present at

this stage of

development. The

limbs will disappear

before birth.

The Whales No external ears – holes are plugged with wax

(in some)

Flukes are horizontal on tail (contrast this with the vertical upper and lower caudal fins in fish)

Blow holes – nose migrated to the top of the head

Blow spouts - water condensation in the lungs, sea water, and mucous; exhale when surfacing then inhale

Cetaceans can fill a lung volume 3000X larger than a human in one half of the time

The Whales

All Cetaceans have a blubber layer

1. increases buoyancy

2. provides insulation against cold water

Very little body hair, produce milk, nurse their young

Mostly marine (approximately 90 species of marine mammals), 5 species of freshwater dolphins

Whale diversity: Baleen and toothed whales

Great whales can be identified from a distance by their blowing

pattern their surface outline at the start of a dive, and how they

dive (portion of their body visible at the end of the dive (fin or

fluke)).

Baleen Whales

Baleen whales have fibrous plates on the upper jaws

1. baleen is made of keratin (protein)

2. there are different types of baleen plates

3. large surface area, strain small planktonic organisms out of the

sea water

4. tongue is used to scrape the plankton off of the baleen plates

Baleen whales are the largest organisms which have ever

lived

Baleen Whales

Among the baleen whales, the females are

much larger than the males

1. females – 110 feet in length

2. males - 80 feet in length

3. weight - 90 to 100 tons (remember that 1 ton

= 2000 lbs)

Bale

en W

hale

sHumpback

Bowhead

Gray

Fin

Blue

MinkeRight

Sei

Baleen Whales Feeding StylesGulping feeding style - huge gulps of water,

accordion pleats on the abdomen (Blue Whale)

Skimming feeding style - leave the mouth open, water moves through the baleen as the whale swims (looks like it is smiling!) - Right Whale

Bottom feeder - stir up sediment on the bottom, filter out the benthic organisms – creates “feeding pits” on the ocean bottom – Gray Whale

Humpback Whales make “bubble curtains” analogous to a net – small plankton will not pass through the bubble curtain – whales take turns feeding in the enclosed area

Comparison of the diet composition of several great whale species.

Comparison of baleen plate filtering mechanisms in great whales.

Toothed Whales

Includes dolphins, porpoises, killer whales

(Orcas), sperm whales

In contrast to the herbivorous baleen

whales, the toothed whales are carnivorous

(have teeth)

70-80 species of toothed whales

Largest toothed whale is the Sperm Whale

Tooth

ed W

hale

s

Sperm Whale

Killer Whale

Dolphins &

Porpoises

Sperm Whale Factoids

Eat giant squid

Can dive 3000 meters and stay submerged

for up to 90 minutes

“Moby Dick” was a sperm whale, based

upon a real rouge Sperm Whale which

ranged off of the Massachusetts coast in

1830's and 1840's which attacked whalers

Sperm Whale Factoids

sperm whales have a substance called

“spermaceti” in their heads which was used for

lamp oil

ambergris - sticky material found in the gut of

sperm whales derived from squid beaks and other

undigested proteins; ambergris is used in the

manufacture of VERY expensive perfume (Older

French scents such as Joy, White Shoulders, etc.)

Toothed Whales

Orca’s striking black and white pattern - counter shading; common to many marine organisms (light on the bottom, dark on the top)

1. eat seals, penguins, large fish

2. will tip over ice flows to get at the seals on the ice

3. travel in pods (small social groups of related members)

4. mate for life

Porpoises have blunter faces than dolphins (extended noses)

Spinner dolphin (Stenella Longirostris)

in the eastern Pacific photographed

alongside a ship.

Dolphins

Highly social

Live in pods

Ride bow waves from boats and whales –allows them to swim fast with very little effort.

Dolphins use echolocation to find prey…similar to the mechanism used in bats.

Pacific white-sided dolphin (Lagenorhynchus obliguidens) cruises

in the bow wake of a research vessel.

Echolocation in dolphins uses a series of clicks created by pushing

air through the melon and internal passages.

Naval SONAR research in

the Hawaiian islands has

negatively affected the

ability of whales in the area

to hunt and navigate. Whale

strandings in areas of

SONAR research have

increased. Calls for a

moratorium on SONAR

testing in areas where

whales and dolphins feed,

breed, and migrate have

increased.

Dolphin

Beluga

Humpback

Day 2

Cetacean Social Interactions Toothed whales are very social and form

social groups

Killer Whales (Orcas) and Sperm Whales form tight pods ( 10 to 40 individuals)

Among Orcas, pods are usually 10 or fewer individuals

a. dominant male

b. mature females

c. calves

d. subordinate males

Cetacean Social Interactions

Sperm whales – pod sizes very in accordance

with the season

a. harem pods

b. nursery pods

c. bulls/schools of mature males

d. schools of calves and juveniles

e. bachelor pods - schools of immature males

Sperm whales will surround an injured pod

member to protect it

Spying behavior in Orcas (a), Sperm Whales surrounding an

injured pod member (b), and bottlenose dolphins carrying a stunned

pod member to the surface so that it can breathe.

Cetacean Social Interactions

Most whales mate belly to belly…this behavior serves other social functions in addition to mating.

Humpback whales have long intricate mating songs (10-15 minutes in length).

Whales songs appear to be socially transmitted; dialects of the songs are specific to regions of the world’s oceans.

Mating behavior in Gray

Whales (a) and Humpback

Whales (b). Mating pair

(a) belly to belly and

supported with the

assistance of a third whale.

Humpbacks actually

surface belly to belly, roll,

and slap flukes as part of

the courtship rituals

leading to mating.

Humpback Whale Songs

For 10 years, Humpback songs off of the eastern Australian coast were consistent.

Two new males appeared from the western Australian coast with a different song pattern.

Within three years, the entire 2000 male population had incorporated themes from common to the western dialect.

This suggests that Humpback Whale song patterns are learned behavior!

Whale Reproduction

whale gestation takes 11-12 months, sperm

whales - 16 month gestation

born tail first to prevent the calf from

breathing in water

once the calf is born, swims to the surface

to breathe

Commerson’s dolphin (Cephalorhynchus commersoni) giving

birth in captivity.

Whales feed in colder polar regions during the summer and migrate to

warmer tropical areas to give birth during the winter. Note that because the

seasons are reversed, northern and southern hemisphere whales never meet.

Whale Reproduction

Birth weight/size in whale calves is relatively large compared to the parent in the mammal world, grow very rapidly

Blue Whale calves gain 200 lbs/day for the first 17 months.

Whale milk is extremely rich, 16-40% fat.

Calves nurse for 4-8 months depending upon the species, calves may also nurse from related females.

Can drink the equivalent of 400 glasses of milk a day

Whale Reproduction

Sperm Whale and Gray Whale mothers are

extremely defensive of their calves.

Whales have very low reproductive rates; this

makes it difficult to replace members removed

from the population at rates exceeding natural

mortality – such as hunting

Mature females reproduce every 1 to 4 years,

baleen whales every 2 years, dolphins every 3-4

years.

Whale Life History Facts

Age at maturity – averages 20 years (9

years for female sperm whales, 20 years for

male sperm whales)

Whale life span: 20 to 40 years on average;

may live to 80 years in the larger baleen

whales

1. Right, bowhead, blue, fin, and humpback whales remain endangered even

though there is an international whaling ban.

2. Seals and sea birds which competed with the great whales for food have all

increased in population size as a result of the demise of the great whales.

Whale Strandings

Occurs more often among the toothed whales –

may relate to the social nature of toothed whales

1. injury to a pod member

2. navigational error

3. food

4. toxins

5. parasites

6. percentage returned to the water is very low, they may

re-strand themselves

Whale Strandings

sperm whales, pilot whales, orcas,

bottlenose dolphins, false killer whales are

the most commonly stranded toothed

whales

20-30 strandings on the GA coast annually,

most frequently bottlenose dolphins or

pigmy killer whales

Order Pinnipedia – Sea

Lions, True Seals,

Walrus

Order Pinnipedia

Streamlined bodies with flippers

Excellent swimmers

Unlike Cetaceans, must come onshore to rest and mate

Restricted to cold water habitats

Layers of blubber – for buoyancy and insulation as in Cetaceans

Predaceous – feed on fish and large swimming invertebrates (nekton)

Pinnipeds

True Seals Sea Lions Walrus

True Seals

Largest group of pinnipeds

Hind flippers can not move forward

Swim by undulating their entire body

No external ears

Harbor seals, elephant seals (largest – males 20 ft), monk seals (Hawaii, Mediterranean – all endangered)

Seals have been hunted traditionally for meat, oil, fur – hunting has been limited to a few native Inuit tribes, seal populations are recovering

Weddell Seal

Leopard Seal

Munk Seals

Elephant Seal

Tru

e S

eals

Sea Lions Can be distinguished from seals by the presence of

external ears

Can turn their rear flippers forward, use front flippers for locomotion (in contrast to seals)

Includes fur seals and the California Sea Lion

Sea lions are killed in fishing nets; killed/shot by fisherman who believe that they are competing with the sea lion for commercial fish.

Sea lions practice harem breeding. Large males are territorial and protect a group of reproductively mature cows.

Steller’s Sea Lion

California

Sea Lion

Northern

Fur SealSea

Lio

ns

&

Eare

d S

eals

Walrus

Only one species of walrus, found in

the Arctic Ocean

No external ears

Tusks appear to be largely used for

mating displays/territorial defense

Benthic feeders

Walrus (Odobenus rosmarus) relaxes on Artic ice.

Order Carnivora – Sea Otters

Sea Otters

spend their entire life in the water (except in the event of severe storm)

no blubber, fur which traps air

eat sea urchins, abalone, mussels, crabs

hold babies on their bellies

live in kelp forests, wrap themselves in fronds of kelp which prevents them from being carried away by currents

Sea Otters

Abalone fishers protest the protection of the sea

otters.

Important relationship between the sea otters, the

sea urchins, and the kelp (keystone predator).

1. Sea otters decline, feeding on sea urchins decline, sea

urchin populations explode.

2. As the sea urchin numbers increase, destruction of the

kelp forests increases.

3. Abalone need the kelp forests to survive.

Order Sirenia – Manatees

and Dugongs

Manatees and Dugongs

Four species (all endangered)

Dugong in East Africa, Western

Pacific Islands and Manatee in

Amazon basin, West Africa, and

the Southeastern United States.

Spend entire life in the water

Herbivorous: graze on Manatee

Grass (Syringodium)

Manatees and Dugongs

Blubber layer present, very wrinkled skin, few

hairs present on face

Extremely slow moving

Nose on top of head at anterior, blow air out when

it surfaces (you can hear it if you are close

enough).

Can reach 15 feet in length, 1300 lbs.

Sirenians produce one calf every three years.

Manatees and Dugongs

The majority of manatee deaths in the US:

boating accidents, especially in Florida as

coastal development increases.

Order Sirenia,

“Sea Cows”

Manatee

Dugong