Diving by Marine Mammals Summary

Lecture focuses on physiological adaptations of diving mammals, integrating concepts of oxygen, carbon dioxide, and internal transport.
Key questions:
- How do marine mammals meet metabolic energy/O2 demands during long periods underwater?
- How do they cope with high pressures at depth?

Weddell seals:
- Extensively studied due to predictable surfacing locations.
- Researchers can collect samples without sedation because they are tolerant of humans.
Elephant seals:
- Migrate long distances and spend most of the year at sea.
- Maximum dive observed for an elephant seal is $1600$ m.

Diving depth depends on diet.
- Crabeater and Leopard seals: brief, shallow dives for krill and penguins.
- Weddell and Elephant seals: deeper dives for fish, squids, and crustaceans.
Sperm whales routinely dive $40-50$ minutes to depths of $1900-2000$ m.
Cuvier’s beaked whales dive for more than $2.5$ h to depths of $2990$ m.

Three major internal O2 stores:
- Bound to blood haemoglobin
- Bound to muscle myoglobin
- Air in the lungs
Tissues function aerobically during short dives but rely on anaerobic metabolism for skeletal muscle during longer dives.
Diving mammals reserve O2 for essential tissues (heart, lungs, brain) via vasoconstriction.
Lactic acid accumulates in muscle cells during dives due to lack of circulation.
Size of total O2 store determines how long a mammal can stay submerged.
- Accomplished divers have higher blood volumes (e.g., elephant seals: $200-250$ ml/kg).
- Higher myoglobin concentrations in skeletal muscles.

Bradycardia: decrease in heart rate during diving.
Regional vasoconstriction
Graded vasoconstriction allows aerobic function to continue during short dives, avoiding anaerobic metabolism.
Some seals modify the number of red blood cells during dives, increasing them while diving and reducing them via storage in the spleen when on land, which reduces blood viscosity.

Reduced metabolic rate during diving reduces O2 consumption and lactic acid buildup.
Tissue cooling reduces brain O2 consumption; Hooded seals don’t shiver underwater.
Delay in food processing.
Limit cost of swimming by gliding and other high efficiency locomotion.
High blood buffering capacities to manage CO2 and lactic acid accumulation.

Alveolar collapse prevents N2 transfer from lung air into blood.
Structural reinforcement in lungs causes respiratory parts to collapse.
Slow ascent may allow N2 to outgas from tissue and body fluid without bubble formation.

Alveolar collapse also prevents O2 transfer to the blood.
Prevents partial pressure from dropping so low when the animal surfaces that the animal loses consciousness.