96 



Fishery Bulletin 104(1) 



Results 



The model was able to fit the ENP index of juvenile goli- 

 ath grouper very well but could not reconcile the conflict- 

 ing trends indicated by the DeMaria and REEF indices 



Figure 4 



Selection curves used to represent the vulnerability of 

 goliath grouper [Epinephelus itajarat to (A) the overall 

 fishery and (B) Everglades National Park anglers. The 

 logistic curves shown in (Al were fitted to either age- 

 composition data derived from the Everglades National 

 Park (ENPl creel census or opportunistic samples from 

 offshore fishing trips (Bullock et al., 1992). 



DeMaria 



1970 



Year 

 Figure 5 



Base model fitted to the four indices of abundance for goliath grouper iEpinepheliis 

 itajara) in southern Florida. 



for adult goliath grouper (Fig. 5). The estimated trends 

 in spawning biomass were rather uncertain (Fig. 6A), 

 but nevertheless indicated a rapid decline to about 5% of 

 virgin levels by the time the harvest ban was imposed in 

 1990, followed by a significant increase. The estimates of 

 fishing mortality were also somewhat uncertain, but gen- 

 erally indicated a gradual increase in fishing mortality 

 to moderate levels during the 1970s followed by a rapid 

 increase during the 1980s (Fig. 6B). The harvest mora- 

 torium was estimated to have been about 83% effective 

 in reducing fishing mortality, nevertheless losses owing 

 to human activities (e.g., illegal harvest and release mor- 

 tality of animals caught at depth) were still estimated 

 to be substantial (F =0.05/yr). If, in accordance with 

 the Gulf of Mexico Management Council's generic Sus- 

 tainable Fisheries Act amendment, the limit reference 

 point is taken to be the equilibrium spawning biomass 

 corresponding to a spawning potential ratio of 50% , then 

 the model indicates that current fishing mortality rates 

 are near F^^c, and that there is less than a 50% chance 

 the stock will recover within 15 years (Fig. 7). 



Sensitivity runs were conducted to examine the im- 

 plications of 1) dropping one or more of the indices, 

 2) increasing the assumed minimum age represented 

 in the REEF and DeMaria indices from 6 to 10, 3) 

 assuming that the historical period began in 1950 

 rather than 1900 and using the anecdotal informa- 

 tion as a tuning index and (4) using the alternate 

 fishery selection curve that was fitted to the data from 

 Bullock et al. (1992), where adult animals were much 

 more vulnerable to the fishery than were juveniles. Of 

 these, the results were most sensitive to removal of the 

 DeMaria index — the projected trends being much more 

 optimistic (Fig. 8). This is because the DeMaria index 

 indicates that the adult population increased rapidly 



during the first few years of 

 the harvest ban, but then 

 suffered a set back in 1999 

 and has since leveled off. In 

 contrast, the REEF index in- 

 dicates that the population 

 continued to increase during 

 that time. Thus, when the 

 DeMaria index is removed, 

 the model allows for a faster 

 postmoratorium increase in 

 the adult population by esti- 

 mating a low fishing mortal- 

 ity rate of about 0.01/yr (i.e., 

 a harvest ban that is 97% 

 effective). The fishing mor- 

 tality rate estimates for the 

 1980s are also lower without 

 the DeMaria index inasmuch 

 as the DeMaria index indi- 

 cates a more precipitous de- 

 cline during that time than 

 the ENP index (the REEF 

 index does not begin until 

 1994). 



2000 



Anecdotal 



1950 1960 1970 1980 1990 2000 



