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Marine Mammal Locomotion

Challenges I. Hydrodynamics II. Energetics

Adaptations

III. Morphology IV. Swimming Mechanics V. Behavior

LOCOMOTION

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Challenges I. Hydrodynamics II. Energetics

Adaptations

III. Morphology IV. Swimming Mechanics V. Behavior

LOCOMOTION

I. HYDRODYNAMICS

Properties of Water Affect Locomotion

• Mammals neutrally buoyant in H2O

– Gravity not important

• Resistance in H2O > resistance in air

– 800x denser

– 30x more viscous

• Drag (resistance) increases with velocity

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I. HYDRODYNAMICS

Drag:

= ½ r V2 A Cd

Physical force resisting forward motion

I. HYDRODYNAMICS

Swim Speed vs. Effort in Dolphins

(Yazdi et al. 1999)

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Types of Drag

I. HYDRODYNAMICS

1. Frictional Drag

4. Wave Drag 2. Form Drag

3. Induced Drag

Types of Drag

I. HYDRODYNAMICS

4. Wave Drag 2. Form Drag

3. Induced Drag 1. Frictional Drag

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1. Frictional Drag:

I. HYDRODYNAMICS

interaction of H2O with animal’s skin

- Important if animal small (i.e., plankton)

- Forces are tangent

Water is like syrup

1. Frictional Drag

Types of Drag

I. HYDRODYNAMICS

4. Wave Drag

3. Induced Drag

2. Form Drag

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displacement of H2O equal to animal’s frontal

surface area

I. HYDRODYNAMICS

2. Form Drag:

- Forces are perpendicular - Body shape is important

Turbulent

Laminar

Stre

amlin

ing

incr

ease

s

Large area of flow separation

Drag

Drag

Drag

Drag

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Turbulent vs. Laminar Flow

• Turbulent: water flow past skin comes off in eddies

= rough flow

I. HYDRODYNAMICS

Laminar flow minimizes drag, which minimizes energy used for swimming

• Laminar: water flow past skin flows in parallel streams

over entire body

= smooth flow

2. Form Drag

1. Frictional Drag

Types of Drag

I. HYDRODYNAMICS

4. Wave Drag

3. Induced Drag

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3. Induced Drag:

I. HYDRODYNAMICS

redirection of flow due to lift

- Increases with “angle of attack”

5O angle of attack

45O angle of attack

drag

drag

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3. Induced Drag:

I. HYDRODYNAMICS

redirection of flow due to lift

- Increases with “angle of attack” - Appendages maximize lift-to-drag ratio

3. Induced Drag

2. Form Drag

1. Frictional Drag

Types of Drag

I. HYDRODYNAMICS

4. Wave Drag

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I. HYDRODYNAMICS

energy lost while splashing at surface

4. Wave Drag:

- less drag when swim submerged

Surface

Submerged

Drag forces 4x higher at the surface!

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I. HYDRODYNAMICS

energy lost while splashing at surface

4. Wave Drag:

- less drag when swim submerged

- breath-holding at a premium

Challenges I. Hydrodynamics II. Energetics

Adaptations

III. Morphology IV. Swimming Mechanics V. Behavior

LOCOMOTION

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II. ENERGETICS

Cost of Transport

• Measure of efficiency of locomotion • COT = metabolic cost of moving 1 unit of body mass 1 unit distance at some speed (e.g., kJ / kg*m)

Met

abo

lic r

ate

Speed

Swimmer

Runner

II. ENERGETICS

Cost of Transport

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Predicted Optimal Range of Speed

for Dolphins

Yazdi et al. (1999)

II. ENERGETICS

Effect of Body Size on COT

(Full and Tu 1991)

II. ENERGETICS

Larger animals have lower relative locomotion costs

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Effect of

Phylogeny on

COT

(Full and Tu 1991)

II. ENERGETICS

Why is it higher?

Cost of ENDOTHERMY!

COT = metabolic rate / speed

II. ENERGETICS

Effect of

Locomotion Mode

on COT

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II. ENERGETICS

Effect of

Locomotion Mode

on COT

Bird

Fish

Mammal

This study was confounded by

phylogeny

All mammals

II. ENERGETICS

Effect of

Locomotion Mode

on COT

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Important to Minimize Drag

• Decrease cost of swimming

• Decrease oxygen consumption

• Swimming more efficient over evolutionary time

– Morphological changes in body shape & propulsive

surface area

– Mechanical changes in swim stroke

– Behavioral “tricks”

Challenges I. Hydrodynamics II. Energetics

Adaptations

III. Morphology IV. Swimming Mechanics V. Behavior

LOCOMOTION

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Challenges I. Hydrodynamics II. Energetics

Adaptations

III. Morphology IV. Swimming Mechanics V. Behavior

LOCOMOTION

III. MORPHOLOGY

Streamlining

- Reduces pressure drag - Measured using Fineness Ratio

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III. MORPHOLOGY

Fineness Ratio

– index of streamlining

– FR = body length / body diameter

– Optimum FR range = 3 – 7

– Ideal FR = 4.5

3.3 – 6.0

4.0 – 11.0

9.0+

Fineness Ratio

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Fineness Ratio

Northern right whale dolphin = 9 - 11

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III. MORPHOLOGY

Specialized appendages for propulsion

- Inter-digital webbing, to fins, to large SA flukes

- Increased surface area over evolutionary time

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Case Study:

Humpback Whales

• Longest flippers: 1/3 body length!

• Tubercles on leading edge

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Case Study:

Humpback Whales

• Longest flippers: 1/3 body length!

• Tubercles on leading edge

WHY?

http://videos.howstuffworks.com/planet-green/32998-g-word-gotta-be-the-tubercles-video.htm

Frank Fish discusses humpback whale tubercles and Whale Power

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Humpback Whales • Decreased drag

• Enhanced lift

• High maneuverability

III. MORPHOLOGY

- Turbulence is behind the animal

Propulsion moves from anterior to posterior

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III. MORPHOLOGY

- reduced cost of transport

Large body size

- Increased O2 stores + increased efficiency in O2

use = increased time submerged to minimize

wave drag

Challenges I. Hydrodynamics II. Energetics

Adaptations

III. Morphology IV. Swimming Mechanics V. Behavior

LOCOMOTION

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IV. SWIMMING MECHANICS

Continuous Propulsion

- Propel-recover-propel stroke cycle replaced by

propulsion over entire stroke cycle:

Dog paddling: ½ propulsion ½ recovery

Fluking: down and upswing of flukes

provide equal propulsive force

Polar Bear

•Not streamlined

- Form drag

•Forelimbs pull animal through water

(“crawl”), hind limbs trail behind

•Surface swimmer

–Wave drag

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Polar Bear

Sea otter

• Amphibious

• Pelvic paddle and pelvic undulation

• Surface swimmer -wave drag

• Somewhat streamlined (FR = 6)

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Sea otter

Otariids • Foreflipper locomotion

• Highly stable at low speeds

• FR = 3 – 6 (optimal range)

• Propulsion through most of cycle

• Highly maneuverable

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Otariids

Phocids,Cetaceans, Sirenians

• Thunniform Mode of Swimming:

2. Dorso-ventral = up-down (Cetaceans & Sirenians)

1. Lateral = side-to-side (Phocids)

- Propulsion from posterior ½ to ⅓ of body

- Constant propulsion

- Two Types:

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Phocids

Cetaceans & Sirenians

Phocids

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Sirenians (and Cetaceans)

Pinniped terrestrial locomotion

Phocids: • body undulations

(mostly vertical, some ice seals lateral) • do not use hind flippers

Otariids: • walk on all 4 limbs • reflect hind limbs forward

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Pinniped terrestrial locomotion

Power vs. Maneuverability

IV. SWIMMING MECHANICS

Trade-off: What makes you fast also makes you less maneuverable

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Stability Factors

1. Control surfaces located far

from center of gravity

2. Concentration of control

surface area posterior of

center of gravity

3. Anterior position of center

of gravity

4. Dihedral of control surfaces

5. Sweep of control surfaces

6. Reduced motion of control

surfaces

7. Reduced flexibility of body

- More “stable” design

- More powerful (fast)

- More efficient at fast speeds

- Much more maneuverable!

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Power vs. Maneuverability

IV. SWIMMING MECHANICS

Trade-off: What makes you fast also makes you less maneuverable

Power vs. Maneuverability

IV. SWIMMING MECHANICS

Trade-off: What makes you fast also makes you less maneuverable

How does a dolphin catch a fish??

Fish should be able to out-maneuver the fast but rigid dolphin

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100

1000

10000

0.001 0.01 0.1 1

Dolphins 20% (this study)Fish 20%Dolphins 20% (Fish, 2002)

Tu

rnin

g r

ate

(o/s

ec)

r/LTurning radius (r/L)

dolphins (Fish 2002)

prey fish

(Maresh et al. 2004)

“Pinwheeling”

- Previous studies looked at maneuverability from the perspective of the animal’s center of gravity

- Flexibility around the rostrum more ecologically relevant measure of maneuverability

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100

1000

10000

0.001 0.01 0.1 1

Dolphins 20% (this study)Fish 20%Dolphins 20% (Fish, 2002)

Tu

rnin

g r

ate

(o/s

ec)

r/L

dolphins (Fish 2002)

prey fish

Turning radius (r/L)

dolphins (Maresh et al. 2004)

?

Case Study:

Spinner Dolphins

WHY?

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Case Study:

Spinner Dolphins

• Acoustic communication

• Precise ranging and bearing of schoolmates

• Dominance

• Courtship

• Remora dislodgment

Theories include:

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Challenges I. Hydrodynamics II. Energetics

Adaptations

III. Morphology IV. Swimming Mechanics V. Behavior

LOCOMOTION

V. BEHAVIOR

Increased time submerged

- Drag can increase

4X when swimming at

surface

- Effect of wave drag

disappears at 3 – 4

body lengths beneath

surface

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V. BEHAVIOR

Swimming at Optimal Speeds

– “Cruising” speed: 2.0 – 3.0 m/s

– Olympic swimmer max: 2.3 m/s

– Marine mammal max “sprint” speed varies

Marine mammal swim speeds

Cruise speeds

Sprint speeds

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V. BEHAVIOR

Porpoising at high speeds

• Have to surface to breathe

• Cost due to wave drag

• Less drag in the air than in water (less dense)

V. BEHAVIOR

Stroke-and-Glide Swimming

•Stroking costs energy

• Gliding is “free”

• Gliding takes advantage of natural changes in buoyancy with depth

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V. BEHAVIOR

Wave (or “Wake”) Riding Bow Riding

Catching a Free Ride

Bow Riding

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Wave Riding Dolphins

Heart Rate

Lactic Acid

Respiration Rate

- Used by immature cetaceans

-“Free ride” from mother’s wake • Calf can swim farther and faster

V. BEHAVIOR

Catching a Free Ride

Echelon Position

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Case Study:

Eastern Tropical Purse-Seine Tuna Fishery

Case Study:

Eastern Tropical Purse-Seine Tuna Fishery

- High-speed, long-duration chase

- Historically high dolphin by-catch

- Back-down procedure minimized by-catch

- Populations not recovering …WHY?

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Case Study:

Eastern Tropical Purse-Seine Tuna Fishery

- 75 – 95% of lactating females caught in nets unaccompanied by calves

= Calves cannot achieve and sustain chase speeds

Mom’s evasive behavior + disruption of echelon + calf underdevelopment

Noren et al. 2010

Case Study:

Eastern Tropical Purse-Seine Tuna Fishery

- Dolphin chase: 20 min at 3 m/s

- Escape: 100 min at 3 m/s

RESULT: Mother and calf separated by over 20 km

Noren et al. 2010

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http://www.arkive.org/polar-bear/ursus-maritimus/video-06b.html Watch this video of polar bear swimming:

Watch how sea otters swim:

http://www.arkive.org/sea-otter/enhydra-lutris/video-ne08a.html

http://www.arkive.org/sea-otter/enhydra-lutris/video-ne00.html

http://www.arkive.org/galapagos-sea-lion/zalophus-wollebaeki/video-wo00.html

http://www.arkive.org/galapagos-sea-lion/zalophus-wollebaeki/video-wo06b.html

http://www.arkive.org/galapagos-sea-lion/zalophus-wollebaeki/video-wo08a.html

FAST

http://www.arkive.org/guadalupe-fur-seal/arctocephalus-townsendi/video-00.html

Watch Otariid swimming:

SLOW

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Phocid swimming:

http://www.arkive.org/weddell-seal/leptonychotes-weddellii/video-08.html

http://www.arkive.org/brown-fur-seal/arctocephalus-pusillus/video-09b.html

Walking Otariid: Phocidulating Phocid: http://www.arkive.org/common-seal/phoca-vitulina/video-06.html

http://www.arkive.org/spinner-dolphin/stenella-longirostris/video-lo12b.html

Spinner dolphin aerial spins:

Bow riding:

http://www.arkive.org/hectors-dolphin/cephalorhynchus-hectori/video-00.html

Dugong swimming:

http://www.arkive.org/dugong/dugong-dugon/video-06.html http://www.arkive.org/dugong/dugong-dugon/video-03.html