Marine Mammal Bioacoustics Cetacean Gross Anatomy

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Marine Mammal Bioacoustics Cetacean Gross Anatomy

• Peter M. Scheifele MDr, PhD, LCDR USN (Ret.)
• University of Cincinnati
• Communication Sciences and Disorders,
  Neuroaudiology Dept.
• University Medical Center
• scheifpr_at_uc.edu

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CETACEAN GROSS ANATOMY

• Fully aquatic mammals
• More auditory than visual

Photo P.M. Scheifele
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Adaptations for Aquatic Life

• Skin increased insulation through the
  development of blubber.
• Circulatory System- increased metabolic rates,
  countercurrent heat exchange systems and
  shunting to allow for prolonged deep dives.
• Echolocation- production and hearing of high
  frequency sound for navigation and foraging.
• Limbs- changes to enhance locomotion
• Heavily Lobulated Kidneys- for conservation of
  water and efficiency at concentrating urine.
• Respiratory System- modified to allow for
  prolonged deep dives.

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Skull

• Primate skull not telescoped with greatly
  inflated cranium and absent rostral area
• Occipital
• Temporal bone and ear are one.
• Skull is symmetrical.
• Two nares.
• Mandible

• Skull is telescoped.
• Occipital bone forms the back of the skull with
  nasal, frontal and parietal bones in between
  (premaxilla and maxilla extend posteriorly and
  laterally such that they override the frontal and
  parietal bones).
• Temporal bone and ear (Bulla) are not connected
• Mysticete maxilla extends posteriorly under the
  orbit.
• Odontocete skull is asymmetrical.
• Two nares in Mysticetes one in Odontocetes.
• Pan Bone present in Odontocetes.

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Minke Whale(Balaenoptera acutorostrata)
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Beluga Whale(Delphinapterus leucas)
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Dentition

• Formula 2/2,1/1,2/2,3/3 32
• Teeth are heterodont and highly specialized.
• Teeth consist of inner material (dentine) covered
  by enamel.

• Formula varies in Odontocetes and total tooth
  number for each side of the jaw is combined as a
  single number such as 0/25 for Sperm Whales and
  65/58 for the Spotted Dolphin.
• Teeth are nearly homodont.
• Exceptions are the Narwhal and Mysticetes.
• 3. Tooth material same as other mammals.

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Dentition Mysticetes

• Complete absence of teeth except in fetal whales.
• Baleen plates protrude ventrally from the outer
  edges of the maxilla.
• Base of the Baleen plates are embedded in the
  epidermal pad of the palate
• Plates grow continuously and are worn down by the
  tongue.
• Plates are covered by sheaths of keratin-filled
  cells
• Outer fringes become worn through use and inner
  fringes become frayed and tangled forming an
  extended filtering surface on the inner side of
  each row of plates.
• The number and length of individual baleen plates
  on each side of the mouth varies

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DENTITION MYSTICETE
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SKELETAL SYSTEM CETACEANS
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SKELETAL SYSTEM- PECTORAL
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Minke Pectoral Structure
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Minke Whale Rib Cage and Vertebrae
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Circulatory System Functions in Marine Mammals

• Transport of Respiratory Gases
• Heat Exchange
• Diving

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Blood Volume

• Man 7 of body weight
• Dog 9 of body weight
• Rabbit 7 of body weight
• Harbor Seal 18 of body weight
• Gray Whale 45 of body weight
• Bottlenose Dolphin 71 of body weight

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Blood Cells and Hematocrit in Marine Mammals

• Red blood cells are same size in diving and
  non-diving animals however, diving mammals have
  higher relative blood volumes and more red blood
  cells.
• Each blood cell tends to be inflated by an extra
  load of hemoglobin.
• This leads to increased hematocrit (packed red
  blood cell volume)
• Higher hematocrit levels (increased oxygen
  storage) may cause a decreased capacity for
  oxygen transport and a limited ability to sustain
  fast swimming speeds.

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Conservation of Oxygen During Dives

• Lower metabolic rate
• Increase quantity of circulatory hemoglobin
• Increase circulating blood capacity
• Use of a control mechanism to allow cardiac
  output to selectively distribute to organs and
  tissues that are life-essential and incapable of
  anerobic metabolism

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Heart, Spleen and Circulatory Pathways

• In-general, deeper diving species tend to have
  enlarged hearts.
• Structure of the heart of whales generally
  resembles that of other mammals.
• In some (such as Fin and Sperm Whales) there is a
  bulbous expansion of the aortic arch.
• Circulatory system is characterized by groups of
  blood vessels (retia mirabilia) for heat
  conservation and blood reservoirs.
• Relative to body size veins are not as enlarged
  as Pinnipeds.
• Spleen size is small (0.02 of body weight as
  compared to 0.3 body weight of terrestrial
  animals).

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Oxygen Capacity

• Diving animals tend to have the highest
  blood-oxygen capacity.
• Dive time is roughly proportional to the total
  oxygen capacity of circulating blood volume.
• Acid-Base equilibrium of the blood in cetaceans
  is considerably altered during long dives
• Respiratory Acidosis during dives
• Metabolic Acidosis during recovery

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Cardiac Function

• Heart Rate
• Voluntary slowing or even bradycardia occurs
  during diving.
• Bradycardia may be as much as 50 (90 bpm to 12
  bpm in Orca, Gray, Pilot and Pacific Bottlenose
  Dolphin)
• Progressive cardio rhythmic change during
  prolonged apneic diving
• General bradycardia
• Prolonged diastole
• Gradual diminishing of P waves
• Cardiac Output
• Decreased in proportion to heart rate
• Stroke volume unchanged
• Blood Pressure
• Indicative of widespread vasoconstriction
• Diastolic pressure maintained by stretching of
  elastic arterial walls during and immediately
  following systole
• Expansion of aortic arch

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How Does Blood-Flow Distribution Affect Dives?

• Requirements
• Oxygen stores in blood, lungs, and muscle
  myoglobin at the onset of dives are insufficient
  to meet consumption requirements for the dive
  duration
• Oxygen content of arterial blood decreases
  linearly during dives with the remaining oxygen
  content as the limiting factor on dive time
• Mechanisms
• Oxygen requirements during dives are decreased
• Available oxygen is redistributed so as to
  conserve the total available amount
• Decreased muscle blood flow
• Increased blood flow to the brain

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Venous Structure and Function

• Venous structures of the abdomen of cetacea
  provide for unusually large stores of blood.
• Sphincter located in inferior vena cava at the
  diaphragm is operative during prolonged dives.
• Retia mirabilia are arteriovenous plexuses
  composed of vascular bundles enclosing many small
  branches of mixed arterial and venous branches.
• Major cerebral supply is derived from the dural
  arterial rete network.
• Rete plexuses also located in flippers, fins, and
  tail flukes as a countercurrent heat exchanger
  and for perfusion of peripheral structures.
• Surface integument is also highly vascularized.

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Respiratory System I

• Begins with external nares (blowhole(s)) and ends
  with lungs.
• Most cetaceans have a blowhole (Odontocetes) or
  blowholes (Mysticetes) on top of head. Sperm
  Whale blowhole is located on anterior top end,
  slightly left of center.
• Opening of nares is accomplished by contraction
  of skeletal muscle but closure is a passive
  process via dense fibrous connective tissue (rich
  with adipose tissue).
• The blowhole represents a major adaptation to
  aquatic life.

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Respiratory System II

• Larynx is composed of cartilaginous framework
  held together by a series of muscles.
• Odontocete larynx has two elongate cartilages
  providing a more direct connection between nose
  and trachea than is found in Mysticetes.
• Trachea is short and broad, consisting of several
  cartilaginous rings that are interconnected with
  each other.
• Odontocete tracheal rings are closed and form a
  non-collapsing tube not in Mysticetes.

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Lungs

• Distinct anatomy from all other mammals in shape
  and lack of lobes.
• Occasionally the apical part of the right lung is
  prominent, resembling the apical lobe of the
  lungs of other mammals.
• Right lung usually larger, longer and heavier
  with marked asymmetry from the left lung related
  to heart position in the chest cavity (for
  rorquals, dolphins, Sperm and Beluga whales).
• Comparative lung volume is lower for cetaceans
  than for terrestrials.
• Lungs have greater rigidity and elasticity with
  increased cartilaginous support.
• Septa projecting into the proximal portion of the
  air sacs contain heavy myoelastic bundles in
  baleen, sperm and bottlenose whales.
• In smaller toothed species these bundles are
  atrophied but a series of myoelastic sphincters
  are found in smallest branchioles.
• Sphincters and muscles may act to close air sacs
  while the elastic portion facilitates rapid
  expiration.

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Breathing

• Apneuristic breathing short breath-hold
  ventilatory pattern
• Upward blow of air from blowholes clears water
  from the area also expiration of an emulsion of
  fine oil droplets from cells lining the air
  sinuses, mucus from tracheal glands and
  surfactants from lungs.
• During inhalation extensive elastic tissue in
  lungs and diaphragm are stretched by muscular
  activity in the diaphragm and intercostal
  musculature.
• These fibers recoil during exhalation to rapidly
  and nearly empty the lungs.
• Oxygen uptake within alveoli may be enhanced as
  lung air is moved into contact with the walls of
  the alveoli by kneading action of small muscle
  fibers scattered throughout the lungs.

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Diving

• Cetaceans typically dive with full lungs.
• Lungs and rib cage are modified to allow lungs to
  collapse as pressure increases.
• Any residual air is squeezed out of alveoli and
  into bronchi and trachea.
• Smooth collapse and reinflation of lungs are
  facilitated by the position of the diaphragm,
  which is set at an acute angle to the long axis
  of the body.
• This allows for toleration of extreme pressures
  during deep dives.
• Allows avoidance of decompression sickness
  (bends) and nitrogen narcosis.

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Diving Biochemistry and Metabolism

• Tissues of marine mammals allow them to survive
  hypoxia and/or ischemia.
• Tissues do not have unusually high capacities for
  anerobic glycolysis.
• Most significant difference in tissue
  biochemistry between diving and non-diving
  animals are levels of myoglobin and muscle
  buffering capacity
• Marine mammals have a great buffering capacity.

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DIGESTIVE SYSTEM FEEDING

• Since Mysticetes are so large, the size disparity
  between them and their prey (plankton) has caused
  them to develop anatomical specializations that
  enable them to exploit these lower trophic level
  prey.
• Mysticetes feed on plankton and small pelagic
  fish usually found between 100 and 500 m.
• Odontocetes eat relatively large and less
  abundant animals.

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DIGESTIVE SYSTEM I

• The cetacean digestive system is characterized by
  an extremely long alimentary canal.
• The esophagus is a long, thick-walled tube, the
  length of which is dependent on the size of the
  animal but which is generally one quarter of the
  total body length in toothed whales.
• The stomach is complex with multiple divisions
  resembling that of ruminants except that its
  organization is different.
• The stomach has four major compartments
• Forestomach having no glands
• Fundic Chamber having folded mucosa and gastric
  glands
• Connecting Stomach between the main and pyloric
  stomach
• Pyloric Stomach which is folded on itself and
  contains glands.
• The forestomach contains high concentrations of
  volatile fatty acids and anaerobic bacteria.

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DIGESTIVE SYSTEMS
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FINI
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References

• Berta, A. and J.L. Sumich (1999) Marine mammals
  evolutionary biology. Academic Press, New York
  494 pp.
• http//www.cartage.org.lb/en/themes/Sciences/Zoolo
  gy/ClassMammalia/GeneralMammalian/GeneralMammalian
  .htm
• Ridgway, S.H. and R. Harrison (eds.) (1989)
  Handbook of marine mammals. Academic Press, new
  york

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Minke Fetal Skeleton
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Beluga Whale OdontoceteSkeletal Structure