Craig et al.: Population biology and harvest of Acanthurus lineatus 
689 
0 8 
06 
0 4 
0.2 
- 
j 
\ K 
f"" 
y" x 
i 1 
♦ ♦ 
22 
21 t" 
20 
0-12 1-12 2-12 3-12 4-12 5-12 6-12 
Selected age range (yr) 
Figure 1 1 
Changes in K and L M based on iterative Ford-Walford re- 
gressions that progressively excluded age classes of 
younger fish. Age-length data used in this calculation were 
derived from a smoothed line of mean size at age. 
Discussion 
The life history traits exhibited by A. lineatus are com- 
mon among coral reef fishes (e.g. Sale, 1991): it is a 
territorial fish that spawns year-round but primarily 
during the austral summer, its pelagic young settle onto 
the reef in a dense pulse and suffer high mortality, sur- 
vivors are sedentary but occasionally relocate to new 
sites, and the fish grow rapidly, have relatively low 
mortality rates after their first year and may live for 
many years. Of particular interest in this study was 
the opportunity to examine fishing pressure on a coral 
reef species. In this instance, the possiblity of emigra- 
tion rates of a “highly site-attached species” and the 
rapid initial growth pattern provide a useful context 
for examining the fisheries data. Additionally, because 
Figure II 2 
Survival index (percentage of fish returning to their terri- 
tories) for newly settled, juvenile and adult A. lineatus at 
the Afao site. 
another data set is available for this species, we were 
able to compare locality-specific demographic traits. 
Emigration 
Acanthurus lineatus is strongly site-attached (adult 
fish have a 99.9%/day return rate to the same site: 
Craig, 1996), but it occasionally switches territories. 
After 3 years of monitoring, 6 of the 45 marked adults 
remained on site (Fig. 12), whereas 23 adults would 
have been present with an annual mortality rate of 
20% as determined by catch curve. The difference 
(17/45) indicates that 38% of the adults that disap- 
peared had probably emigrated to other sites. Craig 
Table 2 
Size, age, maturity, and mortality of A. lineatus in the artisanal fishery in American Samoa, 1987-95. n = sample size. 
1987 
1988 
1990 
1994 
1995 
Mean FL (cm) 
18.2 
17.6 
18.9 
19.3 
18.0 
SE 
0.04 
0.1 
1.0 
0.5 
0.7 
Maximum FL (cm) 
27.7 
28.9 
22.4 
23.0 
23.0 
Mean length-converted age 
4.6 
3.6 
5.7 
6.2 
4.1 
Percent immature 
46 
60 
37 
29 
53 
Total mortality (Z 1 ) 
0.22 
0.23 
0.19 
0.23 
0.25 
(Z 2 ) 
0.25 
0.16 
0.31 
0.23 
0.23 
n 
2,499 
1,126 
329 
720 
745 
Zj = Z derived from a catch curve based on length-converted ages with “adult” VBGF parameters. 
Z 2 = Z derived from a catch curve based on graphical conversion of length to age with the age-length relation. 
