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Fishery Bulletin 90(4). 1992 



170 



160 



150 



^ 140 



« 130 



i 120 



- 110 



o 



> 100 



90 



80 



70 



DOLPHIN OPTIMUM VELOCITY 

 (Vop,=aL0''3) 



80 100 120 140 

 LENGTH (cm) 



Figure 4 



Estimated optimum sustained swimming speed (curved line) 

 of yellowfin tuna Thunnus albacares and spotted dolphins 

 Ste-nella attenuata from the eastern tropical Pacific Ocean. 

 Lengths: fork length for tuna; rostrum to fluke notch ("total 

 length") for dolphins. Vertical bars indicate range of optimum 

 speeds predicted for sizes of tuna and dolphins occurring in 

 mixed associations. Arrows indicate observed average swim- 

 ming speeds of a radio-tagged 96 cm yellowfin tuna and of 

 tagged individual spotted dolphins swimming in situ. Size- 

 ranges for yellowfin tuna ages I-IV, and for spotted dolphins 

 from birth, are indicated above abscissa. 



The term (1.0 -ME) in conjunction with ACT^p ex- 

 presses the fraction of total active metabolism that is 

 dissipated as heat, rather than converted to mechanical 

 energy. The term Hrsp was taken to be zero when the 

 estimate of Hrsp yielded a negative result. In this case, 

 all passive losses were more than offset by heat 

 generated by metabolism. 



Specific rate of unavoidable passive heat loss (HLuspi 

 calories lost passively as heat ■ calories of animal"' • 

 day ') was estimated following Brodie's (1975) pro- 

 cedure for passive losses in large whales, 



HL 



usp 



((21.18/BD J * (37.0 - Ta) * S^/IOOOO.O) * 24 

 WW„*(CDd/1000.0) 



where '^BDa is average blubber depth, CD^ is caloric 

 density of spotted dolphins, 37.0 (°C) is the assumed 

 core temperature for spotted dolphins (Hampton and 

 Whittow 1976), T^ is ambient temperature (assumed 

 constant at 27°C), 21.18 is the conductivity factor for 

 whale blubber (Brodie 1975), and -"8^ is metabolic 

 surface area, estimated as 



S,, = 0.84 *S». 



where VLa = 20.6 and VLb = 0.43, assuming swimming 

 velocity scales with length in the same manner for both 

 spotted dolphins and yellowfin tuna (Fig. 4). Using the 

 same formula and parameters to predict velocity as a 

 function of length in both the tuna and dolphin models 

 maintains comparability between results from the two 

 models. As geometrically similar swimmers, hydro- 

 dynamic constraints should be approximately the same 

 for both tuna and dolphins. 



Specific rate of residual heat loss (HL^sp; calories 

 heat lost in excess of that generated by active and stan- 

 dard metabolism, and specific dynamic action • calories 

 of animal"' • day')'* was estimated as 



HLrsp = HL,3p-(ACT,p*(1.0-ME) + STD3p + SDAsp), 

 where HLrsp>0, otherwise HLrsp = 0. 



"Because spotted dolphins are warm-blooded relative to their en- 

 vironment and because their blubber layer is not a perfect insulator, 

 they will constantly lose heat to surrounding water. If the sum of 

 estimated heat production generated by muscle activity, standard 

 metabolism, and specific heat of digestion equals or exceeds this 

 unavoidable passive loss, the term has no effect. Otherwise, the 

 additional heat loss was added to the animal's energy cost. In prac- 

 tice, the influence of the term was negligible, as differences be- 

 tween Hj and the sum of STD, ACT, and SDA were < 10%. 



Unavoidable heat loss from fins and head is assumed 

 negligible, as blood flow to these areas can be adjusted 

 to minimize or maximize heat loss, as needed. 



Specific dynamic action Specific rate of specific 

 dynamic action (SDA^p; calories lost as heat of diges- 

 tion • calories of animal' • day') was estimated as 



SDAsp = 



SDA*C 



spi 



where SDA (the fraction of consumption converted to 

 heat energy during digestion) = 0.15 for both yellowfin 

 tuna-' and spotted dolphins--. 



Waste losses Specific rate of waste losses (WL^p ; 

 calories lost as feces or urine • calories of animal"' • 

 day"') were estimated as the sum of fractional losses 

 to egestion (F^) and excretion (Ua) 



"BD, = 0.65cm, based on measurements of blubber depth at max- 

 imum girth for a sample of 72 spotted dolphins measuring 80-190 

 cmTL. 



'"S,„ is the surface area of the body beneath the blubber layer. S„, 

 averaged 84% of S„ in the 4-dolphin sample. 



^' Reflecting the relative high-protein low-carbohydrate diet ingested 

 by yellowfin tunas (Olson and Boggs 1986). 



'" SDA is primarily a function of the protein content of ingested food, 

 and is ~15% for a variety of carnivores, including sea otters eating 

 clams and squid (10-13%, Costa and Kooyman 1984), harp seals 

 eating fish (17%, Gallivan and Ronald 1981). and various terrestrial 

 mammals fed a mixed diet (Kleiber 1961). 



