During diving, marine mammals initiate a series of cardiovascular changes that include bradycardia and decreased peripheral circulation. Because heat transfer from thermal windows located in peripheral sites of these mammals depends on blood flow, such adjustments may limit their thermoregulatory capabilities during submergence. Here, we demonstrate how the thermoregulatory responses of bottlenose dolphins (Tursiops truncatus) are coordinated with the diving response. Heart rate, skin temperature and heat transfer from the dorsal fin and flank were measured while dolphins rested on the water surface, stationed 5–50 m under water and floated at the surface immediately following a dive. The results showed that heat flow ranged from 42.9+/−7.3 to 126.2+/−23.1 W m(−)(2) and varied with anatomical site and diving activity. Upon submergence, heat flow declined by 35 % from the dorsal fin and by 24 % from the flank. An immediate increase in heat flow to levels exceeding pre-dive values occurred at both sites upon resurfacing. Changes in heart rate during diving paralleled the thermoregulatory responses. Mean pre-dive heart rate (102.0+/−2.6 beats min(−)(1), N=26) decreased by 63.4 % during dives to 50 m and immediately returned to near resting levels upon resurfacing. These studies indicate that heat dissipation by dolphins is attenuated during diving. Rather than challenge the diving response, heat transfer is delayed until post-dive periods when the need for oxygen conservation is reduced.

REFERENCES

Elsner
R.
,
Kenney
D. W.
,
Burgess
K.
(
1966
).
Diving bradycardia in the trained dolphin
.
Nature
212
,
407
–.
Hampton
I. F. G.
,
Whittow
G. C.
(
1976
).
Body temperature and heat exchange in the Hawaiian spinner dolphin, Stenella longirostris
.
Comp. Biochem. Physiol
57
,
196
–.
Hampton
I. F. G.
,
Whittow
G. C.
,
Szekerczes
J.
,
Rutherford
S.
(
1971
).
Heat transfer and body temperature in the Atlantic bottlenose dolphin, Tursiops truncatus
.
Int. J. Biometeorol
15
,
247
–.
Handrich
Y.
,
Bevan
R. M.
,
Charrassin
J.-B.
,
Butler
P. J.
,
Putz
K.
,
Woakes
A. J.
,
Lage
J.
,
LeMaho
Y.
(
1997
).
Hypothermia in foraging king penguins
.
Nature
388
,
64
–.
Hill
R. D.
,
Schneider
R. C.
,
Liggins
G. C.
,
Schuette
A. H.
,
Elliott
R. L.
,
Guppy
M.
,
Hochachka
P. W.
,
Qvist
J.
,
Falke
K. J.
,
Zapol
W. M.
(
1987
).
Heart rate and body temperature during free diving of Weddell seals
.
Am. J. Physiol
253
,
344
–.
McGinnis
S. M.
,
Whittow
G. C.
,
Ohata
C. A.
,
Huber
H.
(
1972
).
Body heat dissipation and conservation in two species of dolphins
.
Comp. Biochem. Physiol
43
,
417
–.
Schmidt-Nielsen
K.
,
Schmidt-Nielsen
B.
,
Jarnum
S. A.
,
Houpt
T. R.
(
1957
).
Body temperature of the camel and its relation to water economy
.
Am. J. Physiol
188
,
103
–.
Scholander
P. F.
,
Schevill
W. E.
(
1955
).
Counter-current vascular heat exchange in the fins of whales
.
J. Appl. Physiol
8
,
279
–.
Skrovan
R. C.
,
Williams
T. M.
,
Berry
P. S.
,
Moore
P. W.
,
Davis
R. W.
(
1999
).
The diving physiology of bottlenose dolphinsT. M. WILLIAMSANDOTHERS2769 Thermoregulation in diving dolphins (Tursiops truncatus). II. Biomechnaics and changes in buoyancy at depth
.
J. Exp. Biol
202
,
2749
–.
Thompson
D.
,
Fedak
M. A.
(
1993
).
Cardiac responses of grey seals during diving at sea
.
J. Exp. Biol
174
,
139
–.
Williams
T. M.
,
Friedl
W. A.
,
Haun
J. E.
(
1993
).
The physiology of bottlenose dolphins (Tursiops truncatus): heart rate, metabolic rate and plasma lactate concentration during exercise
.
J. Exp. Biol
179
,
31
–.
Williams
T. M.
,
Haun
J. E.
,
Friedl
W. A.
(
1999
).
The divingphysiology of bottlenose dolphins (Tursiops truncatus). I. Balancing the demands of exercise for energy conservation at depth
.
J. Exp. Biol
202
,
2739
–.
Wilson
R. P.
,
Grant
W. S.
,
Duffy
D. C.
(
1986
).
Recording devices on free-ranging marine animals: does measurement affect performance?
.
Ecology
67
,
1091
–.
Zapol
W. M.
,
Liggins
G. C.
,
Schneider
R. C.
,
Qvist
J.
,
Snider
M. T.
,
Creasy
R. K.
,
Hochachka
P. W.
(
1979
).
Regional blood flow during simulated diving in the conscious Weddell seal
.
J. Appl. Physiol
47
,
968
–.
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