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Fishery Bulletin 101(1) 



(A'=0.188), Ralston (1987; Ar=0.188), and Edwards (1985; 

 /i'=0.219) were somewhat similar to that observed in this 

 study (A'=0.187). However, the asymptotic lengths report- 

 ed by Richards' and Ralston (1987) were larger than our 

 estimates, which were again similar to those of Edwards, 

 1985). In contrast, the estimates of A' derived by Brouard 

 et al. (1984), Brouard and Grandperrin (1985), and Mohsin 

 and Ambak ( 1996), which ranged from 0.28 to 0.50, provid- 

 ed overestimates of the growth potential off! multidens as 

 observed in our study. Clearly, methodological differences 

 in age estimation have the potential to unduly influence 

 growth parameter estimation and may provide misleading 

 impressions of the production potential of these fishes. 



The similarity of growth in length-at-age between sexes 

 indicates that there is little trade off in energetic invest- 

 ment into reproductive activity after sexual maturity at 

 the expense of somatic growth as there is for some Lutja- 

 nus species (Newman et al., 1996, 2000b). Information on 

 energy partitioning in the Pristipomoicles is not known. 

 However, females with a large body size would be repro- 

 ductively "fitter" if they could accommodate a large mass 

 of hydrated eggs prior to spawning, especially in a mul- 

 tiple male, multiple female spawning system. 



The long life span of P. multidens and other lutjanid 

 species (Loubens, 1980; Newman et al., 1996, 2000a; New- 

 man and Dunk, 2002; Rocha-Olivares, 1998) may be an 

 evolutionary adaptation that supports iteroparity. Many 

 demersal reef fish are highly fecund, but egg and larval 

 survivorship is low; therefore, spawning over numerous 

 years may be necessary to maintain stable populations. 

 In addition, numerous years of reproductive output may 

 also be required to contend with environmental variability 

 (e.g. the incidence of cyclones. El Nino-La Nina cycling), 

 which may substantially influence recruitment success. 

 Extended periods of high exploitation results in decreases 

 in the spawning stock biomass and constriction of the 

 age structure of fish populations, and thus diminishes 

 the number of effective spawnings. Any reduction in the 

 number of effective spawnings may result in a decrease 

 in ecological fitness and hence limit the adaptive capacity 

 of the species to combat environmental or anthropogenic 

 induced stress. 



Variation in life expectancy due to fishing pressure has 

 the potential to bias estimates of M used in our study. To 

 account for any Af associated difference, a range of M es- 

 timates have been considered in our study. Pristipomoides 

 multidens were fully recruited to the commercial fishery 

 in the NDSF by age 6. Catch-at-age data showed relative- 

 ly consistent estimates of Z among years from 1995-96 

 through to 1997-98 and a relatively broad age structure 

 in the landed catch. 



Fishery management implications 



Throughout much of its range P. multidens composes a 

 significant proportion of the demersal catch of tropical 

 multispecios fisheries. Within these multispccies fisheries 

 P. multidens is taken as part of the directed targ(>t catch 

 or as a part of the retained catch. In fish trawl-based fish- 

 eries, P. multidens can be harvested at all stages of their 



life history from juvenile to adult, making them especially 

 vulnerable to overexploitation. In contrast, fisheries that 

 use trap and line methods of capture (using bait to attract 

 fish) only have the capacity to harvest fish in the subadult- 

 to-adult phase of their life history. Hence, the method of 

 capture and harvest strategy adopted has the capacity to 

 influence the sustainable exploitation of the P. multidens 

 resource. 



Of particular relevance to fishery managers is the ca- 

 pacity that fish trawl-based fisheries have in being capa- 

 ble of continuing to function and to be economically viable 

 (driven by the more productive, lower value species) while 

 populations of higher valued species such as P. multidens 

 become depleted. Thus, careful monitoring of the P. multi- 

 dens resource will be required, particularly in trawl-based 

 fisheries. Fishery managers need to be responsive to the 

 intrinsic vulnerability off! multidens to overhai-vesting as 

 a corollary of its life history characteristics. Furthermore, 

 fish such as P. multidens, which have low rates of natural 

 mortality, low growth potential, extended longevity, ma- 

 ture relatively late in life and are either dead or moribund 

 as a consequence of internal hemorrhaging when the 

 physoclistous is ruptured during capture, are likely to be 

 particularly sensitive to exploitation pressure. The appar- 

 ent low survival rate for released fish in the fishing depths 

 of the NDSF fieet indicates that the traditional use of legal 

 minimum sizes to increase survival to spawning sizes and 

 hence increase overall yields is not a practical option. 



Populations off! multidens have a low productive capac- 

 ity and hence are vulnerable to overfishing as a conse- 

 quence of slow gi-owth, extended longevity, late maturity, 

 and low rates of natural mortality The demersal fish re- 

 sources of the NDSF, of which P. multidens is a significant 

 part, is currently being managed with an innovative total 

 allowable effort system that allocates individually trans- 

 ferable effort units equitably to each licensee. However the 

 highly mobile, efficient, and wide-ranging capacity of the 

 NDSF fleet may require more complex management ar- 

 rangements to maintain future breeding stock levels. The 

 incorporation of appropriately targeted spatial or temporal 

 (or both spatial and temporal) closures within the existing 

 effort management framework is likely to provide an addi- 

 tional useful and robust mechanism to maintain spawning 

 stock biomass and protect against recruitment overfishing. 

 In the wider Indo-Pacific region, fishery managers should 

 consider han'est strategies of low frequency or low intensi- 

 ty in conjunction with targeted spatial or temporal closures 

 to protect the spawning stock biomass of these fishes. 



Harvest strategies such as setting fishing mortality at 

 or hear natural mortality (F=A/) were often prescribed 

 prior to the 1990s (GuUand, 1970). Recently, the adop- 

 tion of harvest strategies such as setting F = F„ , were 

 thought to be quite conset-vative, but usually resulted in 

 F = M harvest strategies (Walters, in press). Following 

 the meta-analysis of Myers et al. (1999), who examined 

 stock-recruitment cui-ve slopes expressed as maximum 

 reproductive rates per spawner at low spawner biomass, 

 Walters (in press) has reported that optimal fishing mor- 

 tality rates are substantially lower than natural mortality 

 rates for most species and stocks. Furthermore, Patterson 



