Marine Mammal Respiration & Diving Physiology MARE 390 Dr. Turner

Diving Most marine mammals spend a significant potion of their time underwater Foraging for food Increase swimming efficiency Reducing metabolic costs Minimizing risk of predation during sleep

Diving Capabilities Measured as maximum depth or duration Phocid N. elephant seal 1530(m) 77(min) S. elephant seal 1430(m) 120(min) Otariid Cal. sea lion 482(m) 15(min) Odobenid Walrus300(m) 13(min)

Diving Capabilities Odontocete Sperm whale 3000(m) 138(min) Mysticete Fin whale500(m) 30(min) Bowhead352(m) 80(min) Sirenian W.I. manatee600(m) 6(min) Dugong400(m) 8(min) Sea otter100(m)

Diving Capabilities

Diving Adaptations Cease breathing during diving events apneic conditions – conflicting conditions 1. O 2 stores ↓ with ↑ activity (O 2 demand) 2. CO 2 & lactate ↑ in blood & muscle During hypoxic events, muscle activity is maintained anaerobically results in ↑ accumulation of lactate

Low-Impact Aerobics In the past yrs – research emphasis on anaerobic dive physiology Recent on aerobic dive limits and how animals stay within these limits Know that aerobic diving is the only way to facilitate multiple sequential dives over a short period of time

Under Pressure Tolerate ↑ in water pressure 1 atmosphere (atm) for each 10m Sperm whale – 3000m (300atm) Squeezes air-filled spaces Absorbing gases at high pressure can be toxic – damage from bubbles Effect upon central nervous system

Out of Circulation Heart similar to other mammals – few adaptations Retia mirabilia – (wonderful net) tissue masses containing extensive spirals of blood vessels (mainly arteries) “red muscle”

Total Body Oxygen Stores Largest O 2 stores in diving marine mammals Hemoglobin – O 2 binding molecule of red blood cells; can deliver O 2 where needed Myoglobin – O 2 binding molecule of muscle cells; delivers O 2 directly to muscles Hematocrit – packed red blood cell volume; hemoglobin volume – higher in mammals with increased diving capacity

Total Body Oxygen Stores Resp – Cardio – Cellular = All Equal Fewer mitochondria Cellular dominant More mitochondria

Total Body Oxygen Stores

Total (L, M, B)

Respiratory System Deep diving marine mammals have flexible chest walls – allow for collapse; lungs airless Trachea supported by cartilaginous rings maintains rigidity while alveoli collapse Lungs not larger than terrestrial mammals but important adaptations

Pinniped Lungs Multiple alveolar sacs in deep diving phocids Phocid OtariidOdobenid

Cetacean Lungs Cetacean lungs – greater elasticity Volume lower in deeper diving species Inability of respiratory tract to store gas WHY? Risks of embolism; bends Efficient air renewal - > 90% in single breath Sirenians – similar Humans – 10%

Total Body Oxygen Stores

Cetacean Lungs Oblique position – empties more completely efficient gas exchange Mysticete Odonticete

Da Bends! Neither pinnipeds or cetaceans use lung volume to supply O 2 during dive Pinnipeds – exhale before dive Cetaceans – inhale before dive Air pushed out of lungs at depth into trachea, bronchi Helps to stave off both bends (gas bubbles in blood) & nitrgogen narcosis (euphoria) “Mini-Ditka, Tirty-tree, New York Giants, Twenty eight” – Bill Swerski

Dugongs & Otters & Bears (Oh My!) Sirenians – long, extend posteriorly to kidneys - 2° buoyancy control Otters – 2.5 times terrestrial mammals; buoyancy control Polar Bear – little to no adaptations

Aerobic Dive Limit Longest dive that does not lead to an increase in blood lactate concentration If dive within ADL, can dive again immediately without recovery period If dive exceeds ADL and accumulate lactate; surface recovery period is required to “burn-off” (remove) lactic acid from the body

Aerobic Dive Limit ADL = Total O 2 store (mLO 2 ) / (Metabolic rate during dive (mL O 2 x min -1 ) Total O 2 store = O 2 in blood, muscle, lungs ↑ ADL = longer and / or deeper the dive Foraging capacity related to the balance b/w total O 2 store and metabolic rate

Dive Response During dive, available O 2 ↓ (hypoxia) and CO 2 ↑ (hypercapnia) Together create asphyxia Counteract with several adaptations: Anaerobic diving – no O 2 ; lactic acid & H+ ions accumulate Bradycardia – decline in heart rate Ischemia – preferential distribution of blood to O 2 sensitive organs; temperature & metabolic rate

Bradycardia Decreased heart rate - modest (sirenians), moderate (cetaceans) extreme (phocids) Measured in diving mammals, birds, and reptiles Ringed Seal

Ischemia A decrease in the blood supply to a bodily organ, tissue, or part caused by constriction of blood vessels Preferentially to “core” organs – Brain, heart Away from skin, muscles, lungs

Aerobic Dive Limit Brain Abdomen Dorsal muscle Declining metabolism during dive

Aerobic Dive Limit During a dive, lactic acid accumulates as a waste product in the muscles; depletes O 2 stores from myoglobin due to ↓ pH

Aerobic Dive Limit O2O2 Lactate Heart

Aerobic Dive Limit Information from archival tag recorders greatly expanded information regarding ADL and dive routine

Aerobic Dive Limit

My Seal Is Broken! Phocids – correlation between body size & dive behavior (larger – longer) Hawaiian monk – typically shallow; deep diving recently identified (550m) Otariids – not as much time diving few minutes, shallow depths

Pinniped Diving Strategy 1. Apnea with exhalation (phocids) or inhalation (otariids) 2. Bradycardia 3. Peripheral vasoconstriction & hypoperfusion 4. Hypometabolism in ischemic tissues 5. Enhance O 2 carrying capacity 6. Spleen for regulating hematocrit (large- phocids; typical - otariids)