I. HYDRODYNAMICS Properties of Water Affect Locomotion Mammals neutrally buoyant in H 2 O Gravity not important Resistance in H 2 O > resistance in air 800x denser 30x more viscous Drag (resistance) increases with velocity
I. HYDRODYNAMICS Drag: Physical force resisting forward motion = ½ r V 2 A Cd
I. HYDRODYNAMICS Swim Speed vs. Effort in Dolphins (Yazdi et al. 1999)
I. HYDRODYNAMICS Types of Drag 1. Frictional Drag 3. Induced Drag 2. Form Drag 4. Wave Drag
I. HYDRODYNAMICS Types of Drag 1. Frictional Drag 3. Induced Drag 2. Form Drag 4. Wave Drag
I. HYDRODYNAMICS 1. Frictional Drag: interaction of H 2 O with animal s skin - Forces are tangent - Important if animal small (i.e., plankton) Water is like syrup
I. HYDRODYNAMICS Types of Drag 1. Frictional Drag 3. Induced Drag 2. Form Drag 4. Wave Drag
I. HYDRODYNAMICS 2. Form Drag: displacement of H 2 O equal to animal s frontal surface area - Forces are perpendicular - Body shape is important
Streamlining increases Large area of flow separation Drag Turbulent Drag Drag Drag Laminar
I. HYDRODYNAMICS Turbulent vs. Laminar Flow Turbulent: water flow past skin comes off in eddies = rough flow Laminar: water flow past skin flows in parallel streams over entire body = smooth flow Laminar flow minimizes drag, which minimizes energy used for swimming
I. HYDRODYNAMICS Types of Drag 1. Frictional Drag 3. Induced Drag 2. Form Drag 4. Wave Drag
I. HYDRODYNAMICS 3. Induced Drag: redirection of flow due to lift - Increases with angle of attack
5 O angle of attack drag 45 O angle of attack drag
I. HYDRODYNAMICS 3. Induced Drag: redirection of flow due to lift - Increases with angle of attack - Appendages maximize lift-to-drag ratio
I. HYDRODYNAMICS Types of Drag 1. Frictional Drag 3. Induced Drag 2. Form Drag 4. Wave Drag
I. HYDRODYNAMICS 4. Wave Drag: energy lost while splashing at surface - less drag when swim submerged
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
Surface Submerged Drag forces 4x higher at the surface!
I. HYDRODYNAMICS 4. Wave Drag: energy lost while splashing at surface - less drag when swim submerged - breath-holding at a premium
Challenges I. Hydrodynamics II. Energetics Adaptations III. Morphology IV. Swimming Mechanics V. Behavior
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)
Metabolic rate II. ENERGETICS Cost of Transport Swimmer Runner Speed
II. ENERGETICS Predicted Optimal Range of Speed for Dolphins Yazdi et al. (1999)
II. ENERGETICS Effect of Body Size on COT Larger animals have lower relative locomotion costs (Full and Tu 1991)
II. ENERGETICS Effect of Phylogeny on COT COT = metabolic rate / speed Why is it higher? (Full and Tu 1991) Cost of ENDOTHERMY!
II. ENERGETICS Effect of Locomotion Mode on COT
II. ENERGETICS Bird Mammal Fish Effect of Locomotion Mode on COT This study was confounded by phylogeny
II. ENERGETICS Effect of Locomotion Mode on COT All mammals
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
III. MORPHOLOGY Streamlining - Reduces pressure drag - Measured using Fineness Ratio
III. MORPHOLOGY Fineness Ratio index of streamlining FR = body length / body diameter Optimum FR range = 3 7 Ideal FR = 4.5
4.0 11.0 Fineness Ratio 3.3 6.0 9.0+
Fineness Ratio Northern right whale dolphin = 9-11
III. MORPHOLOGY Specialized appendages for propulsion - Increased surface area over evolutionary time - Inter-digital webbing, to fins, to large SA flukes
Case Study: Humpback Whales Longest flippers: 1/3 body length! Tubercles on leading edge
Case Study: Humpback Whales Longest flippers: 1/3 body length! Tubercles on leading edge WHY?
Frank Fish discusses humpback whale tubercles and Whale Power http://videos.howstuffworks.com/planet-green/32998-g-word-gotta-be-thetubercles-video.htm
Humpback Whales Decreased drag Enhanced lift High maneuverability
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
V. BEHAVIOR Catching a Free Ride Wave (or Wake ) Riding Bow Riding
Bow Riding
Wave Riding Dolphins Respiration Rate Lactic Acid Heart Rate
V. BEHAVIOR Catching a Free Ride Echelon Position - Used by immature cetaceans - Free ride from mother s wake Calf can swim farther and faster