Thermal windows on the trunk of hauled-out seals: hot spots for thermoregulatory evaporation?
Björn Mauck1,*,
Kerstin Bilgmann2,
Daryl D. Jones3,
Ulf Eysel4 and
Guido Dehnhardt1
1 Allgemeine Zoologie & Neurobiologie, ND6/33, Ruhr-Universität
Bochum, D-44780 Bochum, Germany,
2 Institut für Tierphysiologie, Universität Köln, Weyertal
119, D-50931 Köln, Germany,
3 Ocean Sciences Centre, Memorial University of Newfoundland, St John's,
Newfoundland A1C 5S7, Canada
4 Institut für Physiologie, Abteilung Neurophysiologie, MA4/149,
Ruhr-Universität Bochum, D-44780 Bochum, Germany
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Fig. 1. Thermogram of the harp seal Tyler obtained 62 min after leaving the water.
The thermal window on the left side of the seal is clearly visible and
exhibits temperatures up to 24.2 K higher than those of the rest of the body
surface.
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Fig. 2. Series of thermograms of the harp seal Jamie. Thermal windows are numbered
from cranial to caudal and according to order of their appearance. (A)
Arrangement of thermograms recorded after 19 min and 20 min. The first thermal
windows on the seal's trunk have appeared on the right dorsal body side.
Thermal windows are solitary and of more or less circular shape, and no fusion
of thermal windows has occurred yet. The hind flippers show low surface
temperatures. A temperature profile line (inset) reveals a sharp decrease in
surface temperature between thermal windows 1 and 2. (B) Arrangement of
thermograms recorded after 30 min and 31 min. Thermal windows on the right
dorsal side of the seal's trunk have enlarged and partly fused (Nos. 1–3
and Nos. 4, 5; see also temperature profile line in inset), and new thermal
windows have appeared (Nos. 6–10). (C) Arrangement of thermograms
recorded after 51 min and 53 min. Thermal windows have further enlarged and
fused to coherent areas (Nos. 1, 2, 3, 7, 8, 9, 10 and Nos. 4, 5,
respectively; see also inset), and a new thermal window has just appeared (No.
11). Note that, at this time, hind flippers show high surface temperatures as
well (No. 12).
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Fig. 3. Series of thermograms of the harbour seal Nick showing the process of
fusion of thermal windows in detail. (A) Thermogram recorded after 7 min. Two
solitary thermal windows with surface temperatures 15 K higher than those in
the surrounding areas have appeared on the left lateral neck region. A
temperature profile line (inset) shows the first stage of fusion of these
thermal windows. The surface temperature between thermal windows is elevated
(approximately 21°C) but is clearly lower than temperatures within the
thermal windows (approximately 29–31°C; see inset). (B) Thermogram
recorded after 11 min. Fusion of thermal windows 1 and 2 is almost complete,
but both thermal windows can still be identified. A temperature profile line
shows only a slight decrease of temperatures between thermal windows (see
inset). (C) Thermogram recorded after 50 min. Fusion is complete, the
resulting thermal window has further enlarged and former thermal windows 1 and
2 can no longer be identified. A new thermal window (No. 3) with slightly
elevated surface temperatures (see also inset) has just appeared. (D)
Thermogram recorded after 55 min. Thermal windows have further enlarged. The
new thermal window, No. 3, almost reaches the peak temperature of the old
thermal window, while the region in between the thermal windows is still cold
(see inset).
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Fig. 4. Series of thermograms of the grey seal Laslo. (A) Thermogram recorded after
53 min. Thermal windows appear on the back of the head, the shoulder/neck
region and the fore flipper. Thermal windows are clearly separated (see
inset). (B) Thermogram recorded after 77 min. Thermal windows on the seal's
body have enlarged and partly fused (Nos. 4, 5, 7; see also inset), while
thermal windows on the right fore flipper remain comparatively cold. New
thermal windows have just appeared on the seal's back (Nos. 8, 11). (C)
Thermogram recorded after 89 min. Thermal windows on the seal's back have
further enlarged and fused (Nos. 5, 7; see also inset), and thermal window 8
is fully developed.
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Fig. 5. Series of thermograms of the harp seal Jamie. Thermal windows are numbered
from cranial to caudal and according to order of their appearance. (A)
Arrangement of thermograms recorded after 29 min, 30 min and 32 min. Multiple
thermal windows on the seal's trunk have appeared on the left dorso-lateral
body side, contralateral to the side the seal is lying on. Thermal windows are
solitary and of more or less circular shape; no fusion of thermal windows has
occurred yet. The head (Nos. 1, 2) and the hind flippers (No. 13) show high
surface temperatures as well, while the left fore flipper shows rather low
temperatures. (B) Arrangement of thermograms recorded after 43 min and 45 min.
Thermal windows on the seal's trunk have enlarged and partly fused (Nos. 6, 7
and Nos. 8, 9, 10), and new thermal windows have appeared (Nos. 14–16).
(C) Arrangement of thermograms recorded after 62 min and 64 min. Thermal
windows have further enlarged and fused to more or less coherent areas (Nos.
5–11 and Nos. 12, 13).
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Fig. 6. Series of thermograms of the harbour seal Henry obtained in summer
(A–D) and winter (E–F). Note that the temperature range
represented by the colour scale has been altered (16.8–37.0°C in
A–D versus 6.0–33.0°C in E–F) in order to
guarantee the best temperature resolution. (A) Arrangement of thermograms
recorded after 10 min. Thermal windows have appeared on the hind flippers and
in the dorsal neck/shoulder region (temperature range, 29.9–33.7°C),
some comparatively small thermal windows have just appeared on the seal's back
(31.1–32.6°C), while the other body regions are clearly colder
(25.1–29.0°C). (B) Arrangement of thermograms recorded after 20 min
and 21 min. Thermal windows have enlarged with slightly increased temperatures
(30.2–35.1°C), and thermal windows are also visible on the right
fore flipper (31.3–33.8°C). Although the area between thermal
windows on the seal's back is already comparatively warm (approximately
29.3°C), the remaining body surfaces are still rather cold
(25.6–28.1°C). (C) Arrangement of thermograms recorded after 29 min
and 30 min. Thermal windows fuse to a rather coherent area (temperature range,
30.9–35.6°C), while the remaining body surfaces are still clearly
colder (26.3–28.3°C). (D) Arrangement of thermograms recorded after
44 min and 45 min. Thermal windows have completely fused to a coherent area
covering the seal's back and flippers (30.4–37.1°C). The lateral
body regions clearly remain colder (26.2–28.1°C). (E) Arrangement of
thermograms recorded after 44 min and 48 min. Some rather small thermal
windows are visible on the seal's head and hind flipper region, while a fully
developed thermal window covers the dorsal neck region
(22.4–30.3°C). (F) Arrangement of thermograms recorded after 75 min
and 77 min. While thermal windows seem not to have changed size, the thermal
window covering the dorsal neck region shows a similar range of temperatures
(22.3–30.1°C) but, on average, has become clearly cooler because
high temperature areas within the thermal window have decreased in size. It
can be speculated that this thermal window has already been closed and the
respective body surface is now being cooled by the rather cold ambient
air.
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© The Company of Biologists Ltd 2003
