The cardiorespiratory, metabolic, and thermoregulatory physiology of juvenile northern elephant seals (mirounga angustirostris)

• Main Author: Andrews, Russel D.
• Format: Thesis
• Language: English
• Published: 1999
• Subjects: Elephant Seals
• Online Access: http://hdl.handle.net/2429/9934

Heart rates, respiratory frequencies, field metabolic rates (FMR) and body temperatures of northern elephant seals diving at sea and during apnoea on land were monitored to gain insight into the ability of elephant seals to make repetitive, long duration dives. Juvenile northern elephant seals were captured at Afio Nuevo, CA, instrumented, and translocated to release sites around Monterey Bay. Data were recorded with custom data loggers and analogue Holter monitors during the seals' return to Ano Nuevo and during apnoea and eupnoea on land after they hauled out on the beach. Diving patterns were very similar to those of naturally migrating juveniles. The heart rate response to apnoea at sea and on land was a prompt bradycardia, but only at sea was there an anticipatory tachycardia before breathing commenced. Heart rate at sea declined by 64% from the surface rate of 107±3 beats min⁻¹ (mean ± SD) while heart rate on land declined by 31% from the eupnoeic rate of 65±8 beats min⁻¹. Diving heart rate was inversely related to dive duration in a non-linear fashion, best described by a continuous, curvilinear model, while heart rate during apnoea on land was independent of apnoea duration. Occasionally, instantaneous heart rate fell as low as 3 beats min⁻¹ during diving. Although bradycardia occurred in response to apnoea both at sea and on land, only at sea was heart rate apparently regulated to minimise eupnoeic time and to ration oxygen stores to ensure adequate supplies for the heart and brain not only as the dive progressed normally, but also when the dive was abnormally extended. The mean respiratory frequency (fR) during the first min after a dive was 22.0 ± 2.0 breaths min⁻¹, which was 2.4 times greater than fR after an apnoea on land, despite that the mean dive duration was not different from the mean duration of apnoea on land. The higher f[sub R] at sea permits elephant seals to spend only short periods at the surface for gas exchange, resulting in quick recovery from long dives and a high percentage of time spent submerged. The at-sea FMR was no different from the onshore FMR, even though seals at sea were swimming almost continually in cold, highly conductive water and seals onshore were usually just resting. This may be partially due to a regulated heat loss and temperature reduction at the onset of long duration diving that possibly reduces diving metabolic rate through a reduction in thermoregulatory costs and a Q₁₀ related decrease in metabolism. Science, Faculty of Zoology, Department of Graduate