332 



Abstract — Using a bioenergetics 

 model, we estimated daily ration and 

 seasonal prey consumption rates for 

 six age classes of juvenile sandbar 

 sharks (Carcharhinus plumbeus) in 

 the lower Chesapeake Bay summer 

 nursery area. The model, incorporat- 

 ing habitat and species-specific data 

 on growth rates, metabolic rate, diet 

 composition, water temperature (range 

 16.8-27.9 "O, and population struc- 

 ture, predicted mean daily rations 

 between 2.17 ±0.03 (age-0) and 1.30 

 ±0.02 (age-5) % body mass/day. These 

 daily rations are higher than earlier 

 predictions for sandbar sharks but 

 are comparable to those for ecologi- 

 cally similar shark species. The total 

 nursery population of sandbar sharks 

 was predicted to consume -124,000 kg 

 of prey during their 4.5 month stay 

 in the Chesapeake Bay nursery. The 

 predicted consumption rates sup- 

 port the conclusion that juvenile 

 sandbar sharks exert a lesser top- 

 down effect on the Chesapeake Bay 

 ecosystem than do teleost piscivores 

 and humans. 



Estimating consumption rates of juvenile 

 sandbar sharks (Carcharhinus plumbeus) 

 in Chesapeake Bay, Virginia, 

 using a bioenergetics model* 



W. Wesley Dowd^ 



Richard W. BrilP 



Peter G. BushnelP 



John A. Musick' 



' Department of Fisheries Science 

 Virginia Institute of Marine Science 

 1208 Create Road, P.O. Box 1346 

 College of William and Mary 

 Gloucester Point, Virginia 23062 

 Present address (lor W Dowd) Graduate Group in Ecology 



Dept Wildlife, Fish and Conservation Biology 



University of California 



One Shields Avenue 



Davis, California 95616 

 E-mail address (for WW Dowd) wwdowdia)ucdavis edu 



^ Virginia Cooperative Marine Education and Research Program 

 Virginia Institute of Marine Science 

 1208 Create Road, PO. Box 1346 

 College of William and Mary 

 Gloucester Point, Virginia 23062 



' Department of Biological Sciences 

 Indiana University South Bend 

 1700 Mishawaka Avenue 

 South Bend, Indiana 46634 



Manuscript submitted 29 October 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



15 September 2005 by the Scientific Editor. 



Fish. Bull. 104:332-342 (2006). 



The lower Chesapeake Bay, Mid- 

 Atlantic Bight, and adjacent coastal 

 lagoon systems serve as the primary 

 summer nursery areas for the North- 

 west Atlantic Ocean sandbar shark 

 {Carcharhinus plumbeus) population 

 (Musick et al., 1993), Sandbar sharks 

 are the most abundant large coastal 

 sharks in the Mid-Atlantic Bight 

 (Musick et al., 1993) and an impor- 

 tant part of the commercial shark 

 catch. After the rapid expansion of the 

 fishery in the mid 1980s, the sandbar 

 shark population in Virginia's coastal 

 ocean waters declined by approxi- 

 mately 66% by 1991 (Musick et al., 

 1993). Meanwhile, catch rates in the 

 lower Chesapeake Bay, the core nurs- 

 ery area for juvenile sandbar sharks, 

 remained relatively stable (Musick et 

 al., 1993). Because juvenile sandbar 

 sharks return to the coastal or estua- 

 rine nursery grounds for the first four 



to six summers of life (Sminkey and 

 Musick, 1995; Grubbs et al., in press), 

 these nursery grounds are vital to the 

 life history and potential recovery of 

 the Northwest Atlantic sandbar shark 

 stock (Branstetter, 1990; Hoff and 

 Musick, 1990; Sminkey and Musick, 

 1996; Cortes, 1999). 



Despite the abundance and posi- 

 tion of elasmobranchs at the apex of 

 many coastal and pelagic food webs, 

 their energetic demands and the role 

 of elasmobranchs as predators have 

 rarely been quantified (Gruber, 1985; 

 DuPreez et al., 1990; Sundstrom and 

 Gruber, 1998; Lowe, 2002; Schindler 

 et al., 2002). In the Chesapeake Bay, 

 sandbar sharks occupy an apex posi- 

 tion in the food web, preying upon 



' Contribution number 2721 from Virginia 

 Institute of Marine Science, College of 

 William and Mary, Gloucester Point, VA. 



