236 



Abstract.— Sandbar sharks iCarcha- 

 rhinus plumbeus) support an impor- 

 tant commercial fishery. They are man- 

 aged as a component of a multispecies 

 group, termed large coastal sharks, by 

 the National Marine Fisheries Service 

 (NMFS) under the Fishery Manage- 

 ment Plan (FMP) for Atlantic sharks. 

 Currently, large coastal sharks, gener- 

 ally, and sandbar sharks, specifically, 

 are considered overfished. Several man- 

 agement options, including nursery 

 ground closures and size limits, are 

 being considered to conserve the fish- 

 ery. We explored the implications of 

 management options for large coastal 

 sharks within the framework of a stage- 

 based model. Based on biological crite- 

 ria, the life cycle of the sandbar shark 

 was represented as five stages: neonate, 

 juvenile, subadult, pregnant adults, and 

 resting adults. The model followed only 

 females. From a fishing mortality rate 

 (F) of 0.20, estimated in the 1996 stock 

 evaluation workshop (SEW), the model 

 projects a population decline to 13% of 

 its current abundance within 20 years. 

 The population is not stabilized until 

 F is reduced to 0.07. In one run of the 

 model, we assumed that F on neonates 

 and pregnant adults was zero in order to 

 assess the impact of a "perfect" nursery 

 ground closure. Under this scenario, the 

 population continued to decline unless 

 F on the remaining stages was reduced 

 to 0.097. Even with the closure of nurs- 

 ery grounds or the introduction of size 

 limits to protect neonates and juveniles, 

 F has to be reduced substantially. The 

 model is highly sensitive to the dynam- 

 ics of juveniles and subadults, which 

 implies that management should pro- 

 tect these immature sharks to rebuild 

 the stock. 



Management of the sandbar shark, 

 Carcharhinus plumbeus: 

 implications of a stage-based model* 



Karyl K. Brewster-Geisz 



Highly Migratory Species Management Division 



National Manne Fisheries Service 



1315 East West Highway 



Silver Spring. Maryland 20910 



E-mail address Karyl Brewster Geisz 3 noaa gov 



Thomas J. Miller 



Chesapeake Biological Laboratory 



University of Maryland Center for Environmental Sciences 



P O Box 38 



Solomons, Maryland 20688-0038 



Manuscript accepted 26 November 1999. 

 Fish. Bull. 98:236-249 (2000). 



The sandbar shark (Carcharhinus 

 plumbeus) is a species of primary 

 importance in the Atlantic and Gulf 

 of Mexico shark fishery (NMFS, 

 1993; NMFSi; Branstetter and Bur- 

 gess- ). It is managed as a part of the 

 large coastal shark group defined 

 under the Atlantic shark Fishery 

 Management Plan (FMP; NMFS, 

 1993). Since the mid 1980s, the 

 demand for shark has increased 

 (NMFS, 1993). The fishery peaked 

 in 1989 with landings of approxi- 

 mately 4600 metric tons (t) dressed 

 weight ( dw; NMFS-^ ). Catch per unit 

 of effort of large coastal sharks 

 declined rapidly during the 1970s 

 and 1980s. To prevent overfishing, 

 the FMP imposed an annual quota 

 of 2570 t dw from 1994 to 1996 for 

 the large coastal fishery, required 

 mandatory reporting of landings, 

 and prohibited the removal of fins 

 (NMFS, 1993). At the 1996 stock 

 evaluation workshop (SEW), scien- 

 tists found no evidence of improve- 

 ments in the large coastal stocks 

 and recommended reducing fishing 

 mortality by SC}^ (NMFS, 1996). 

 In response, the National Marine 

 Fisheries Service (NMFS) reduced 

 the annual quota in 1997 by SC^ 

 to 1285 t dw and reported to Con- 

 gress that large coastal sharks were 



overfished (NMFS, 1997). The most 

 recent data indicate that fishing 

 mortality rates have not declined 

 as much as expected and may still 

 be too high to stabilize the sandbar 

 shark stock (NMFS^). A size limit 

 equivalent to approximately 12-13 

 years of age (140 cm fork length) 

 was recommended. 



The NMFS is mandated, through 

 the Magnuson-Stevens Fishery Con- 

 servation and Management Act, to 



* Contribution 3264 of the University of 

 Maryland Center for Environmental Sci- 

 ences Series, Chesapeake Biological Labo- 

 ratory, University of Maryland, Solomons, 

 MD 20688-0038." 



' 1996. Report ofthe shark evaluation work- 

 shop. Southeast Fisheries Science Center, 

 Natl. Mar Fish. Serv., NOAA. Miami, FL, 

 80 p. 



- Branstetter, S., and G. Burgess. 1997. 

 Continuation of an observer program to 

 characterize and compare regional efforts 

 in the directed commercial shark fishery 

 in the eastern Gulf of Mexico and South 

 Atlantic. Gulf and South Atlantic Fisher- 

 ies Development Foundation, Inc.. Tampa, 

 FL. University of Florida, Gainesville, FL., 

 83 p. 



' 1997. Shark evaluation annual report. 

 Southeast Fisheries Science Center, Natl. 

 Mar Fish. Serv.. NOAA, , Miami, FL, 12 p. 



^ 1998. Report of the shark evaluation work- 

 shop. Southeast Fisheries Science Center, 

 Natl. Mar. Fish. Ser\'., NOAA, Panama City, 

 FL. 



