Relationship between red blood cell lifespan and endogenous carbon monoxide in the common bottlenose dolphin and beluga

Certain deep-diving marine mammals (i.e., northern elephant seal (Mirounga angustirosis), Weddell seal (Leptonychotes weddellii)) have blood carbon monoxide (CO) levels that are comparable to those of chronic cigarette smokers. Most CO produced in humans is a by-product of heme degradation, which is released when red blood cells (RBC) are destroyed. Elevated CO can occur in humans when RBC lifespan decreases. The contribution of RBC turnover to CO concentrations in marine mammals is unknown. Here, we report the first RBC lifespans in two healthy, marine mammal species with different diving capacities and heme stores, the shallow diving bottlenose dolphin (Tursiops truncatus) and deep-diving beluga (Delphinapterus leucas) and relate the lifespans to the levels of CO in blood and breath. The belugas, with high blood heme stores, had the longest mean RBC lifespan compared to humans and bottlenose dolphins. Both cetacean species were found to have three times higher blood CO content compared to humans. The estimated CO production rate from heme degradation indicates some marine mammals may have additional mechanisms for CO production, or delay CO removal from the body, potentially from long duration breath-holds.