The effect of hypercapnia on respiratory characteristics and diving behaviour of freely diving seals.

Three trained young seals, one harp seal, Pagophilus groenlandicus, and two hooded seals, Cystophora cristata, have been used to study the effect of hypercapnia on respiratory characteristics and diving behaviour. The seals were allowed free movements within a circular pool, while diving and respiratory behaviour were recorded. During the experiments the alveolar CO2 tension was continually recorded. There was a significant decrease in duration of dives with increasing Paco2 for all animals. Ve increased significantly with increasing Paco2. This increase was caused by more frequent surfacing rather than by a higher respiratory frequency during the breathing periods. Tidal volume increased from 3 to 43% when inspired CO2 was increased from 0.03 to 9 vol%. The seals were all found to be less sensitive to CO2 than man. A decreased sensitivity to CO2 with age is suggested from the results.