Heart rate and body temperature during free diving of Weddell seals

Abstract

We have developed and successfully used the first microprocessor-controlled monitors for collection of data on depth, heart rate, and body temperature of one fetal and five adult male freely swimming Weddell seals. Adult seals almost invariably experienced a prompt bradycardia at the start of each dive, and the mean heart rate during diving was significantly lower for dives greater than 20 min (P greater than 0.999). The heart rate was also significantly greater during the ascent portion of dives when compared with the descent portion (P greater than 0.95). The fetal seal experienced a slow onset of bradycardia when its mother dived; during diving the fetal heart rate decreased by an average of 1.1 beats/min for each minute of the dive. The fetal heart rate generally took approximately 10 min to recover to predive levels after its mother resurfaced to breathe. The body temperature of one adult male Weddell seal showed a decrease of greater than 1.5 degrees C from resting levels before dives of greater than 15 min were initiated and a drop of over 2 degrees C before dives of greater than 30 min duration.

Deep-diving sea lions exhibit extreme bradycardia in long-duration dives

“…In dives greater than 6 min in duration, minimum ƒ H was usually less than 10 beats min −1 and sometimes as low as 6 beats mins −1 (Fig. 5B), which is similar to extreme divers such as emperor penguins (3 beats min −1 ), elephant seals (3 beats min −1 ), grey seals (2 beats min ), and even as low as what was observed in forced submersion studies (Scholander, 1940;Hill et al, 1987;Thompson and Fedak, 1993;Andrews et al, 1997;Meir et al, 2008). Thus, similar to phocids, the extreme bradycardia exhibited during forced submersions is also a routine component of the sea lion's physiological repertoire, allowing them to perform long-duration dives.…”

“…As in other freely diving mammals and penguins studied (Millard et al, 1973;Hill et al, 1987;Thompson and Fedak, 1993;Andrews et al, 1997;Boyd et al, 1999;Williams et al, 1999;Green et al, 2003;Froget et al, 2004;Meir et al, 2008), California sea lions also exhibited a gradual tachycardia as they began ascent, with the rate of increase escalating during the last 15-30 s of the dive. It has been proposed that the ascent tachycardia may increase blood flow and O 2 delivery to O 2 -depleted tissues, thus lowering the P O2 in the blood and increasing the blood/lung O 2 gradient, resulting in shorter surface intervals by maximisation of O 2 uptake at the surface (Thompson and Fedak, 1993).…”

“…Although California sea lions are not usually considered exceptional divers, they exhibited extreme bradycardia, comparable to that of the best diving phocids (Hill et al, 1987;Thompson and Fedak, 1993;Andrews et al, 1997), during their deep dives. In dives greater than 6 min in duration, minimum ƒ H was usually less than 10 beats min −1 and sometimes as low as 6 beats mins −1 (Fig.…”

Challenges of measuring body temperatures of free-ranging birds and mammals

“…Regardless of such shortcomings, thermometry remains an inexpensive, fast, and attractive method for body temperature recording, especially when cross-sectional data are desirable and subjects can be caught and measured with relative ease. With larger animals, measurements of blood and muscle temperature may be made by percutaneous insertion of a thermistor via a catheter and temperature logged with a surface-mounted recorder [33][34][35]. This allows for continuous monitoring of body temperature while animals are exhibiting natural behaviours but requires recapture of the animal for removal of instrument.…”

In pursuit of Irving and Scholander: a review of oxygen store management in seals and penguins

“…Combined with the relatively mild bradycardias of free-diving Weddell seals (Hill et al, 1987), this finding suggested that muscle blood flow persisted to some degree during free dives and that the blood O 2 store was not isolated from muscle. This contrasted with the severe bradycardia and peripheral vasoconstriction during forced submersions.…”