323 



Abstract — Standard and routine 

 metabolic rates (SMRs and RMRs, 

 respectively) of juvenile sandbar 

 sharks iCarcharhinus plumbeus) were 

 measured over a range of body sizes 

 (n=34) and temperatures normally 

 associated with western Atlantic 

 coastal nursery areas. The mean SMR 

 Qii, (increase in metabolic rate with 

 temperature! was 2.9 ±0.2. Heart rate 

 decreased with increasing body mass 

 but increased with temperature at a 

 Q,Q of 1.8-2.2. Self-paired measures 

 of SMR and RMR were obtained for 

 15 individuals. Routine metabolic rate 

 averaged 1.8 ±0.1 times the SMR and 

 was not correlated with body mass. 

 Assuming the maximum metabolic 

 rate of sandbar sharks is 1.8-2.75 

 times the SMR (as is observed in 

 other elasmobranch species), sandbar 

 sharks are using between 34V( and 

 100*^ of their metabolic scope just 

 to sustain their routine continuous 

 activity. This limitation may help 

 to explain their slow individual and 

 population growth rates, as well as 

 the slow recoveries from overfishing 

 of many shark stocks worldwide. 



Standard and routine metabolic rates of 

 juvenile sandbar sharks iCarcharhinus plumbeus), 

 including the effects of body mass and 

 acute temperature change* 



W. Wesley Dowd' 



Richard W. Brill^ 



Peter G. BushnelP 



John A. Musick' 



' Department ol Fisheries Science 

 Virginia Institute ol Marine Science 

 1208 Create Road, PO, Box 1346 

 Gloucester Point, Virginia 23062 

 Present address (for W W. Dowd): Department ol Wildlife, Fish and Conservation Biology 



University of California Davis 



One Shields Avenue, 



Davis, California 95616 

 E-mail address (for W W Dowd) wwdowd gucdavisedu 



^ Virignia Cooperative Marine Education and Research Program 

 Virginia Institute of Marine Science 

 1208 Create Road, PO, Box 1346 

 Gloucester Point, Virginia 23062 



^ Department of Biological Sciences 

 Indiana University South Bend 

 1700 Mishawaka Avenue 

 South Bend, Indiana 46634 



Manuscript submitted 21 August 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



26 September 2005 by the Scientific Editor. 



Fish. Bull. 104:.323-331 (2006). 



Shark populations continue to suffer 

 from overfishing throughout the North- 

 west Atlantic and worldwide (Baum et 

 al.. 2003). The sandbar shark iCarcha- 

 rhinus plumbeus) can serve as a model 

 for overfished coastal shark species, 

 many of which share ecological and 

 ecophysiological characteristics. After 

 the rapid expansion of the Atlantic 

 coastal commercial shark fishery in 

 the mid-1980s, sandbar shark num- 

 bers declined 66% by 1991 (Musick 

 et al., 1993; Sminkey and Musick, 

 1995). Like many of their K-selected 

 relatives, sandbar sharks grow slowly 

 and mature after a minimum of 13-15 

 years (Casey and Natanson, 1992; 

 Sminkey and Musick, 1995). Demo- 

 graphic models of these species predict 

 very slow rates of population increase 

 even in the absence of fishing pressure, 

 and elasticity analyses of these models 

 demonstrate that the juvenile stage 

 is the most critical life history stage 

 (Sminkey and Musick, 1996; Cortes, 

 1999; Brewster-Geisz and Miller, 

 2000). It is necessary, therefore, to 



understand the actual and potential 

 contributions of various juvenile nurs- 

 ery areas to recovery of the Northwest 

 Atlantic sandbar shark population 

 and to recovery of other coastal shark 

 stocks (Branstetter, 1990). 



Bioenergetics models can be used to 

 assess the impacts and requirements 

 of juvenile sharks as apex predators. 

 Metabolic rate is the largest and most 

 variable component of the energy bud- 

 get for active fish species, and it is 

 critical that it be determined accu- 

 rately in order to construct realistic 

 bioenergetics models (Ney, 1993). 

 Systematic metabolic rate data for 

 elasmobranchs are only rarely avail- 

 able, and previous models of sandbar 

 shark bioenergetics have relied upon 

 metabolic rate data from unrelated 

 species (Medved et al., 1988; Stillwell 

 and Kohler, 1993). 



' Contribution number 2720 from Depart- 

 ment of Fisheries Science, Virginia 

 Institute of Marine Science, College of 

 William and Mary, 1208 Create Road, 

 Gloucester Point, VA 23062. 



