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First published online July 20, 2007
Journal of Experimental Biology 210, 2618-2626 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003855

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Differential heating and cooling rates in bigeye tuna (Thunnus obesus Lowe): a model of non-steady state heat exchange

Hans Malte¹, Christina Larsen^1,*, Michael Musyl² and Richard Brill^3,,

¹ Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, Denmark
² Joint Institute for Marine and Atmospheric Research, Pelagic Fisheries Research Program, University of Hawai`i at Manoa, Honolulu, HI 96822, USA
³ Honolulu Laboratory, Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, Honolulu, HI 96822, USA

View larger version (18K): [in this window] [in a new window]   Fig. 1. 3-day depth record for Fish 241, illustrating the typical pattern observed in bigeye tuna not associated with floating objects or seamounts (from Musyl et al., 2003). The black horizontal bars indicate the night time.

View larger version (28K): [in this window] [in a new window]   Fig. 2. Ambient (Ta) and sensor (Ts) temperature records (the latter located within the body of an archival tag placed in the visceral cavity) during a typical daytime period for Fish 241, along with the fitted Ts data. (A) An entire daytime period; (B) the 300–400 min portion in A expanded.

View larger version (30K): [in this window] [in a new window]   Fig. 3. The fitted values of khigh and klow for each daytime period of each fish from the entire data records. Missing values typically resulted from the fish being associated with a Buoy 3 (Fish 301, Fish 390, Fish 392) or Cross Seamount (Fish 224), making fitting impossible. Fish 224 had an apparent constant displacement of the recorded ambient temperature. When this was adjusted by a constant value, such that the night-time sensor temperature excess was similar to that of the other fish, it gave similar fitted values for klow and khigh and therefore the results were included in the figure.

View larger version (7K): [in this window] [in a new window]   Fig. 4. The fitted klow values from all fish plotted as a function of khigh.

View larger version (27K): [in this window] [in a new window]   Fig. 5. (A) Red muscle temperature (Trm) of Fish 241 (calculated from the measured sensor temperature) as a function of ambient temperature (Ta) during one day. The data points are joined to illustrate the behavior of the fish and how this affects its Trm. (B) The distribution of calculated Trm for an ambient temperature interval of 10.0–25.5°C. (C) Density plot of the number of observations (i.e. the number of observations per °C2) of a given combination of ambient and calculated red muscle temperature. This plot is based on the combined set of observations (all days and nights for the entire time of deployment) for Fish 241, Fish 290, Fish 292, Fish 301 and Fish 625, for a total of 921,592 observations. The dotted straight lines in A and C show Ta=Trm.

View larger version (20K): [in this window] [in a new window]   Fig. 6. Vertical swimming speed as a function of depth during one day for Fish 241. As indicated by the arrows, the left side of the figure shows descents and right side ascents.

View larger version (5K): [in this window] [in a new window]   Fig. 7. Mean of all the observed maximal ascent and descent speeds (± s.e.m) during vertical excursions for (from left to right) Fish 390, Fish 392, Fish 301, Fish 298, Fish 625, Fish 241 and Fish 224, plotted as a function of size (fork length, FL). The regression lines were fitted with a weighted linear least-square procedure using the reciprocals of the s.e.m. as weight and are: y=3.627–0.0192x (for descents, r2=0.985, P=0.00015) and y=3.439–0.0195x (for ascents, r2=0.945, P=0.001). Note that the s.e.m. for each point is so small that it is not distinguishable from the symbol. Also the maximal vertical speeds observed for each fish during their entire tag deployment period are shown (filled triangles).