Dowd et a\ Metabolic rates of juvenile Carcharhinus plumbeus 



327 



sandbar sharks recover rapidly from angling stress 

 (6-10 h; Sparge et al.-). There was no evidence of sys- 

 tematic decreases in RMR (relating to recovery from 

 handling stress) during individual RMR experiments, 

 which averaged 16.2 ±2.0 hours in length. Using only 

 the final trial for each individual, we fitted RMR to the 

 allometric equation: 



RMR = 203 (±35) X Af"  



= 16, r'- = 0.78 (9) 



Routine (average ±SEM) swimming speeds decreased 

 with increasing body size according to the exponential 

 equation speed (bl/s) = 3.54 TL"" " (r^^O.lS) (Fig. 4). In 

 most cases the animal maintained a swimming speed 

 and direction along the outer wall of the chamber for 

 5-20 minutes before turning around. Because each 

 shark swam at a relatively constant speed, the effect 

 of swimming speed on metabolic rate could not be 

 determined. 



Paired standard and routine metabolic rates 



Paired SMR and RMR measurements were obtained for 

 15 sharks (1.025-7.170 kg) (Fig. 3). The mean ratio of 

 RMR to SMR at 24°C was 1.8 ±0.1. The mean ratio of 

 RMR^i to SMR was 1.6 ±0.1. There was no significant 

 correlation between body mass and the ratio of RMR to 

 SMR (P=0.93, r'-<0.01}. The allometric exponents for 

 RMR and SMR at 24°C were also not significantly differ- 

 ent (likelihood ratio test, xi=0.002, P=0.96; ANCOVA, 

 logmassxtype interaction, F^ ^5 = 0. 33, P=0.57). 



Discussion 



Effects of body mass and temperature on SMR and RMR 



This study presents the first direct measures of SMR 

 and expands the size range over which SMR and RMR 

 have been reported for continuously active shark spe- 

 cies (Fig. 5). Sandbar shark metabolic rate, like that 

 of a wide variety of species, increases with increasing 

 body mass according to the allometric equation MR = 

 aM'>, with a 6 of ~0.71-0.79 (Schmidt-Nielsen, 1997), 

 The effects of body mass on SMR, RMR, and RMR^, 

 (6 in Eqs. 1-3 and 7-9) in sandbar sharks were simi- 

 lar to published values for other elasmobranchs (e.g., 

 Pritchard et al., 1958; DuPreez et al., 1988; Sims, 1996). 

 The temperature independence of 6, previously reported 

 for the lesser sandshark (Rhinobatos armulatus) and the 

 bullray (Myliobatus aquila) (DuPreez et al., 1988), was 

 evident overall in sandbar sharks. However, there was 

 a significant effect of mass on SMR Qjg for the 24-28°C 



2 Sparge, A. L., N. Kohler, G. Skomal, and R. Goodwin. 

 2001. The physiological effects of angling on post-release 

 survivorship in juvenile sandbar sharks ^Carcharhinus 

 plumbeus). (Abstract.) American Elasmobranch Society 

 17'*' Annual Meeting, State College, PA. Website:http://www. 

 flmnh.un.edu/fish/organizations/aes/abst2001d.htm [accessed 

 on 26 September 2005.] 



70 



100 



110 



80 90 



Total length (cm) 



Figure 4 



Mean (±1 SE) voluntary swimming speeds of sandbar 

 sharks (Carcharhinus plumbeus) during RMR experi- 

 ments. The solid line represents the best-fit equation: 

 speed (BL/s) = S.bixUotal length)-'>^\ 



1000 

 800 



600 

 400 



^ 300 



200 



100 

 80 



60 

 0.3 0.4 0.6 0.8 1 2 3 4 6 8 10 



Mass (kg) 



Figure 5 



Standard metabolic rates of active elasmobranch species 

 and tunas as a function of body mass: Isurus oxyrinchus 

 18 = (•, Graham et al., 1990); Sphyrna lewini 21°C 

 (■), 26^0 (0», and 29°C (D) (Lowe, 2001); Negaprion 

 brevirostris 22-25°C (T, Bushnell et al., 1989) and 25°C 

 (0, Scharold and Gruber, 1991); Carcharhinus acrono- 

 tus 28°C (♦, Carlson et al., 1999); C. plumbeus 18°C 



( ), 24°C( ), and 28°C ( ) (present study); 



kawakawa iEuthynjius affinis) 25°C ( , Brill, 1987); 



yellowfin tuna iThunnus albacares) 25"C (-  -, Brill, 

 1987); skipjack tuna iKatsuwonus pelamis) 23.5-25.5°C 

 (-  -, Brill, 1979). Lines are best-fit allometric equa- 

 tions at the stated experimental temperatures. 



range. These two findings appear to contradict each 

 other, but the 24-28°C pattern may be influenced by 

 small sample sizes at larger body masses (only 2 sharks 

 >7.5 kg). 



