How marine mammals dive

Oxygen travels in more than the lungs

Deep-diving mammals do not solve a dive merely by taking an enormous breath. Large blood volumes and high concentrations of hemoglobin carry oxygen in circulation, while myoglobin holds oxygen inside working muscle. The balance among lung, blood, and muscle stores differs by lineage and develops with age, which is why the capacities of an adult deep-diving seal cannot be assigned to every marine mammal. [3][5][6]

The dive response budgets a finite supply

During apnea, heart rate can slow and blood flow can be redistributed, helping match delivery to tissues while muscles draw on local myoglobin. Modern biologging shows that this response is not a single on-off reflex: heart rate and circulation vary with anticipation, exercise, dive duration, depth, and behavior. Many routine dives remain largely aerobic, while longer efforts can increase reliance on anaerobic metabolism. [1][2][3]

Pressure changes the respiratory system

Hydrostatic pressure compresses gas spaces during descent. Flexible chests and pressure-related movement of air away from gas-exchanging regions can reduce pulmonary gas exchange at depth, influencing both oxygen access and nitrogen uptake. Species do not all begin with the same lung volume or use the lung store in the same way, so the shorthand that every whale exhales and collapses its lungs before diving is inaccurate. [2][4]

A dive is one part of a repeated cycle

Descent, foraging, ascent, and surface recovery draw on the same oxygen budget. Tags that record depth, movement, heart rate, and oxygen have revealed gliding, variable cardiac responses, and species-specific dive profiles that a surface observer cannot see. Time at the surface replenishes oxygen and clears metabolic products, so duration, depth, activity, and recovery interval are more informative together than any record dive quoted alone. [1][2][4][5]

Related guides

• Tidepooling without harm
• Food webs and trophic levels