MJU.ImN OF NAaJNE SCIEI'«:I. 64(3): 8S)-873. ~ CAN MARINE PROrEcrED AREASRESIORE AND CONSERVE STOCK ATTRIBUTES OF REEF FISHES? Joel C. Trexler and Joseph Travis ABSTRACT Oneof the proposed benefitsof marine protected areas (MPAs)is to conserve genetic diversity for life-history traits and to restore some semblance of the life history that was expressed before intense exploitation.Strongsize-selective mortality from fishing has promoted an earlier ageandsmallersizeat maturity in many species anda concomitant reduction in subsequent adultbodysizes. These attributes areless economically desirable thanthose of fish from less heavilyexploited stocks. Weattempted to determine whether the establishment of marine protected areas, and the resulting relaxationof the direc- tional selection produced by fishing mortality,wouldpromote a substantial restoration of later ages at maturity. Our quantitative geneticmodels,calibrated with historical data from Gulf of Mexico popu\ationtof red snapper, Lutjanuscampechanus, indicated that adequate variationshould remainfor life-history traits like age at maturity to respond to new fitness profiles. Marine species with planktonic 1arvac, including most economi- cally important fIShes, have high gene-flowrates that will preclude genetic differentia- tion between the no-take MPAs and the rest of the population. Any changes in the life history that are promoted by the n()-take areamay therefore ramify through the entire population. The establishment of no-take MPAswill promote substantial increases in the ageat maturity ifrecruitmcnt into themis not limited by density-dependent mortality. If it is, the benefit of n()-take areas for increasing the age at maturity will be decreased. The no-take MPAs must serveas the major source of recruits for nearbyfishing areas to producethe proposed benefits.The creationof MPAs will not replacethe benefits of limiting ageor sizebiases in harvesting by traditionalfisheriesmanagement. The global decline in quantity and quality of fishing stocks has created a need for new methods of stock management (Botsford et al., 1997). Marine protected areas (MPAs) and fishing no-take zones are proving to be valuable tools for management of marine fiShery resources (Roberts, 1997; Allison et al., 1998; Lauck et al:, 1998). The proposed virtues of MPAs include protection of spawning stock, elevation of recruitment rates, maintenance of the age and size structures of stocks, and preservation of a balance in the frequencies of predatory and prey species (Ballantine, 1991; Bohnsack, 1992; Gubbay, 1995; Shackell and Willison, 1995; Bohnsack and Ault, 1996). One possible benefit of no-take reserves that has received little attention is the protection of genetic resources for life-history patterns within stocks (Plan Development Team, 1990). This benefit is re- lated to the attempt to conserve stock structure, as indicated by molecular genetic mark- ers (Avise, 1998), but is distinct in referring to the genetic basis of the attributes of indi- vidual fiSh that make them economically desirable and sustain higher population num- bers (Stokes et al., 1993). The most important life-history characters for fishery stocks include the size and age at which individuals mature, the distribution of reproductive effort during life, and age- specific survivorship. Changes in these traits can change the size and age structure of a stock, altering its population dynamics and economic value. For example, a decreasein age at maturity appearsto entail maturation at smaller sizes and an overall decrease in the adult body-size distribution (Trippel, 1995). Although earlier maturation can be associ- as3