604 



Abstract.— We used fishery population 

 models to assess the potential for ma- 

 rine fishery reserves, areas perma- 

 nently closed to fishing, to enhance 

 long-term fishery yields. Our models 

 included detailed life history data. They 

 also included the key assumptions that 

 adults did not cross reserve boundaries 

 and that larvae mixed thoroughly 

 across the boundary but were retained 

 sufficiently to produce a stock-recruit- 

 Aent relationship for the management 

 area. We analyzed the results of these 

 models to determine how reserve size, 

 fishing mortality, and life history traits, 

 particularly population growth poten- 

 tial, affected the fisheries benefits from 

 reserves. We predict that reserves will 

 enhance catches from any overfished 

 population that meets our assumptions, 

 particularly heavily overfished popula- 

 tions with low population growth po- 

 tential. We further predict that re- 

 serves can enhance catches when they 

 make up 40^r or more of fisheries man- 

 agement areas, significantly higher 

 proportions than are typical of existing 

 reserve systems. Finally, we predict 

 that reserves in systems that meet our 

 assumptions will reduce annual catch 

 variation in surrounding fishing grounds. 

 The fisheries benefits and optimal design 

 of marine reserves in any situation de- 

 pended on the life history of the spe- 

 cies of interest as well as its rate of fish- 

 ing mortality. However, the generality 

 of our results across a range of species 

 suggest that marine reserves are a vi- 

 able fisheries management alternative. 



Fisheries benefits and 



optimal design of marine reserves 



Joshua Sladek Nowlis 



Galium M. Roberts 



Eastern Caribbean Center 



University ol the Virgin Islands 



St Thomas, Virgin Islands 00802-9990 



Present address (lor J Sladek Nowlis) Center for Manne Conservation 



580 Market Street, Suite 550 

 San Francisco, California 94104 



E-mail address (for J Sladek Nowlis) JSNowlisMcacmcorg 



Manuscript accepted 28 August 1998. 

 Fish, Bull. 97:604-616 (1999). 



Fishing activity impacts the marine 

 environment in several ways. Indi- 

 vidual species risk severe declines 

 from overexploitation. Over two- 

 thirds of all fisheries world-wide are 

 classified as fished beyond capacity 

 or in danger of becoming so (FAO, 

 1995 ), and higher trophic levels are 

 particularly affected (Pauly et al,, 

 1998). Along with target species, 

 fishing can reduce the populations 

 of nontarget species that are caught 

 and discarded. The ecosystems that 

 support the fisheries also face risks. 

 Fishing can cause biological dam- 

 age to ecosystems when the reduc- 

 tion of key species or trophic levels 

 causes ecological shifts (e.g. Hay, 

 1984; Castilla and Duran, 1985; Hay 

 and Taylor, 1985; Duran and Castilla, 

 1989; McClanahan and Shafir, 1990; 

 Roberts, 1995; McClanahan et al„ 

 1996;Paulyetal., 1998). Fishing can 

 also cause physical damage to ecosys- 

 tems, particularly when dwindling 

 fish catches promote the incentive to 

 use damaging fishing practices 

 (McAllister, 1988), 



Reserves can protect the ecosys- 

 tems within them from damaging 

 fishing practices and have the po- 

 tential to reestablish a natural eco- 

 system balance (Russ, 1985; Plan 

 Development Team, 1990; Roberts 

 and Polunin, 1991; Dugan and 

 Davis, 1993; Roberts and Polunin, 

 1993; Rowley, 1994; Roberts et al„ 

 1995; Bohnsack, 1996). Field stud- 



ies have generally demonstrated that 

 fish stocks build up within a protected 

 area (Roberts and Polunin, 1991; 

 Dugan and Davis, 1993; Rowley, 

 1994; Bohnsack, 1996, and references 

 within) but much less information 

 exists on fishery enhancements. 



In theory, reserves can maintain 

 productive fisheries by protecting a 

 critical stock within their borders. 

 These stocks may enhance catches 

 through adults that grow larger in 

 the reserve and then migrate to 

 fishing areas (adult spillover), or 

 through enhanced recruitment in 

 fishing areas due to increased popu- 

 lation fecundity from the reserve 

 (larval transport). In practice, fish- 

 eries benefits from reserves have 

 rarely been demonstrated or even 

 measured. This lack of field evi- 

 dence reflects the difficulty of per- 

 forming controlled and replicated 

 experiments in unpredictable politi- 

 cal and biological systems. 



The few existing field studies ad- 

 dressing fisheries benefits from re- 

 serves show promise, A marine fish- 

 ery reserve encompassing over 60% 

 of the former fishing grounds north 

 of Mombasa, Kenya, showed a 110'^ 

 increase in catch per unit of effort 

 after only two years (McClanahan 

 and Kaunda-Arara, 1996). Total 

 catches had not yet met those prior 

 to reserve establishment, but trends 

 looked favorable. On Apo Island, 

 Philippines, total fish density and 



