Abstract. -The potential use of 

 marine fishery reserves (MFRs) for 

 managing fisheries on tropical Pa- 

 cific coral reefs was assessed with 

 an extension of the Beverton-Holt 

 model. The effects of year-round 

 fishery closures on harvests in adja- 

 cent, exploited areas were evaluated. 

 Potential changes in spawning stock 

 biomass per recruit (SSB/R) and 

 yield per recruit (Y/R), when vary- 

 ing fractions of exploitable reef area 

 were closed to fishing, were esti- 

 mated from published data, approxi- 

 mated natural and fishing mortality 

 rates, size- and maturity-at-age dis- 

 tributions, and "transfer" (emigra- 

 tion and immigration) rates. For se- 

 lect cases, fundamental transfer 

 rates were adjusted for possible 

 density-dependent emigration from 

 closed areas as relative densities de- 

 creased in surrounding non-closed 

 areas because of continued fishing. 

 Three hypothetical "fish types" were 

 constructed, bracketing the likely ex- 

 tremes in fundamental transfer 

 rates and related life-history param- 

 eters of Pacific coral reef fishes: a 

 small-bodied, fast-growing and 

 short-lived, strongly philopatric spe- 

 cies of damselfish was contrasted 

 with a large-bodied, relatively slow- 

 growing, long-lived, vagile species of 

 jack. A "surgeonfish" type was used 

 to represent intermediate parameter 

 values. 



Simulations corroborate previous 

 observations that MFRs contribute 

 little, if anything, towards increas- 

 ing Y/R. Results for the highly vagile 

 jack confirm that rapid transfer 

 rates will negate potential gains in 

 SSB/R resulting from closures. At 

 the opposite extreme, small reef 

 philopatriots like damselfishes would 

 almost never be harvested, because 

 of negligible transfer rates, unless the 

 MFR was periodically opened to fish- 

 ing. The simulations suggest that the 

 SSB/R of the surgeonfish type is the 

 most likely to benefit from MFRs, be- 

 cause moderate vagility allows bio- 

 mass to accumulate within the clo- 

 sure despite harvesting in the 

 non-closed area. Results further sug- 

 gest that growth rate, fishing effort 

 in the non-closed (open) area, natu- 

 ral mortality, and maturity and har- 

 vesting schedules importantly influ- 

 ence the potential of MFRs to 

 augment SSB when transfer rates are 

 low to moderate. 



Manuscript accepted 5 March 1993 

 Fishery Bulletin 91:414-427 L993 



Modeling the potential of fishery 

 reserves for managing Pacific coral 

 reef fishes 



Edward E. DeMartini 



Honolulu Laboratory, Southwest Fisheries Science Center 



National Marine Fisheries Service, NOAA 



2570 Dole Street. Honolulu, Hawaii 96822-2396 



Marine fishery reserves (MFRs), ar- 

 eas closed to harvesting and adjacent 

 to fished areas, have recently been 

 touted as enforceable and cost-effec- 

 tive alternatives to conventional 

 fisheries management measures such 

 as size and bag limits, closed seasons, 

 and limited entry (Davis, 1989; Plan 

 Development Team 1990; Polacheck, 

 1990; Bohnsack, in press; Davis et al. 1 ; 

 Russ et al., in press). MFRs are rec- 

 ognized worldwide as providing sanc- 

 tuaries in which local populations of 

 desirable species can increase in abun- 

 dance or attain larger body sizes 

 (McCormick and Choat, 1987; Alcala, 

 1988; Buxton and Smale, 1989; Clark 

 et al, 1989; Russ 1985, 1989; Alcala 

 and Russ, 1990; Cole et al, 1990; 

 Bennett and Attwood, 1991). In con- 

 trast, harvesting is known to alter the 

 abundance and body size distributions 

 (Craik, 1981; Katnik, 1982; Koslow et 

 al, 1988; Plan Development Team 

 1990) and assemblage structure (Bell, 

 1983; Russ and Alcala, 1989) of fishes 

 on coral reefs and other localized re- 

 gions of fishery exploitation. 



By providing havens from exploi- 

 tation within which organisms can 

 attain large adult body sizes, desig- 

 nated refuges protect the most valu- 

 able segments of spawning stocks 

 (Plan Development Team, 1990). For 

 most marine organisms with lengthy 



' Davis, G. E., S. C. Jameson, and J. E. Dugan. 

 Potential benefits of harvest refugia in Chan- 

 nel Islands National Park and Channel Is- 

 lands Marine Sanctuary. Unpubl. manuscr., 25 

 p. U.S. Natl. Park Service, Channel Islands 

 National Park. CA 93001. 



(>2 wk-long) planktonic larval stages, 

 MFRs can function as sources of 

 benthic recruits to exploited, often 

 distant, sink populations. The sub- 

 sequent contribution of these recruits 

 to the fishery might counteract (or 

 forestall) the effects of recruitment 

 overfishing (Carr and Reed, in press; 

 Russ et al., in press). Through the 

 directed movements of settled stages, 

 MFRs might also augment the stand- 

 ing biomass of stocks, including 

 spawning adults, in exploited areas 

 adjacent to MFRs as well as within 

 the MFRs themselves (Polacheck, 

 1990; Roberts and Polunin, 1991). 

 MFRs thus might provide a manage- 

 ment tool that addresses growth over- 

 fishing, particularly for multispecies 

 fisheries on tropical coral reefs where 

 conventional management is ineffec- 

 tive (Roberts and Polunin, 1991). 



Despite the recognized importance 

 of MFRs as sanctuaries for conserv- 

 ing biomass, their contribution to 

 fishery stocks and yields in adjacent 

 exploited areas is poorly understood 

 (Davis, 1989; Polacheck, 1990; Rob- 

 erts and Polunin, 1991; Russ et al., in 

 press). An introduction to the prob- 

 lem is provided by Polacheck (1990), 

 who expands the Beverton-Holt equa- 

 tion (Beverton and Holt, 1957) de- 

 scribing the effects of a year-round 

 refuge on the spawning stock biomass 

 (SSB) and yield of a cohort in a sur- 

 rounding exploited area. Although ar- 

 eal closures on coral reefs are one 

 identified application, Polacheck's 

 (1990, Table 1) simulations use 

 empirical data on the growth, matu- 



414 



