Craig et al.: Population biology and harvest of Acanthurus lineatus 
687 
Jan Mar May Jul Sep Nov 
Figure 7 
Monthly changes in “condition factor” of juvenile and adult A. lineatus 
(top), and weights of postabdominal fat bodies (bottom). 
larger size class. At these rates, only 1% (2% x 34%) 
of the population would survive their first year on 
the reef. Thereafter numbers of marked adults de- 
clined rapidly at a loss of 48%/yr (Z=0.65). At these 
rates, the life span of combined life history stages 
would only be about 4-5 years. However, longevity, 
as revealed by otolith analysis, indicated that field 
mortality of marked fish was greatly overestimated. 
Mean ages of artisanal catches were 4-6 years (see 
below) and some fish lived up to 18 years. It is there- 
fore likely that some marked fish emigrated from the 
study area rather than died (see “Discussion” section). 
To obtain a more realistic estimate of adult mor- 
tality, the annual loss of fish in each age class of the 
1994-95 fishery was examined by length-converted 
catch curves calculated in two ways: 1) after conver- 
sion with the VBGF parameters for adult fish (Pauly, 
1983), and 2) after graphical conversion of lengths 
to ages based on the weighted length-age relation 
derived by otolith analysis. The latter was included 
because of the variability of the VBGF parameters 
shown in Figure 11. For fish that were assumed to 
be fully recruited to the fishery, total mortality was 
low in both cases (Z=0.24 and 0.23; Fig. 13), equat- 
