Craig et al.: Population biology and harvest of Acanthurus lineatus 
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CPUE (kg/h) 
Figure 1 5 
Size and CPUE of A. lineatus in the artisanal fish- 
ery from varied sites around Tutuila Island, 
1994-95. 
Comparison of Samoan and Great Barrier 
Reef (GBR) populations 
There are noteworthy differences between A. lineatus 
populations off Samoa and those on the GBR. Fish 
grow larger and live up to twice as long on the Great 
Barrier Reef than those off Samoa (Fig. 16); they are 
also more sparsely distributed and have lower re- 
cruitment rates of newly settled young (Choat and 
Bellwood, 1985; Choat and Axe, 1996; Craig, 1996; 
Choat, unpubl. data). Reasons for these differences 
are speculative and may be complicated by the ex- 
istence of a fishery in Samoa (see section below). 
Perhaps A. lineatus in Samoa is comparatively short- 
lived and maintains its abundance by a high annual 
input of newly settled young. Why there should be a 
greater abundance of newly settled fish in Samoa, 
an oceanic island, than in the extensive reef network 
of the GBR is unclear. 
Fishing pressure 
For at least the past 18 years, the catch composition 
of fish taken by night spear divers has not changed 
greatly, particularly with respect to the prominent 
catch of surgeonfishes (Fig. 17). Although Wass 8 did 
not identify the species composition of the 1977-80 
subsistence catch, local residents report that A. lineatus 
has always been a plentiful and popular food fish. 
Indicators of current levels of fishing pressure were 
ambiguous. Some evidence indicated that overall 
fishing pressure was low: 1) survival rates of fish 
age 1 year and older were high (80% per year), 2) 
estimates of total mortality and the mean size of fish 
in the fishery changed little over a 9-year period, 3) 
there was no relation between fish size and CPUE, 
and 4) an estimate of natural mortality was similar 
to that of total mortality. However, some of these 
points are not overly persuasive. First, estimates of 
natural mortality were derived from empirical equa- 
tions that embody considerable variability (Gulland, 
1984). Second, trends based on fish size are of uncer- 
tain value as indicators of fishing pressure due to 
fish behavior. At night, when A. lineatus is harvested, 
there is an apparent spatial separation of small and 
large fish. Fish less than about 14 cm are not often 
encountered in the areas fished (senior author, pers. 
obs.), perhaps because they remain in shallower ar- 
eas or hide within smaller crevices during the night. 
Thus the larger sizes of fish taken by the spear fish- 
ermen represent those that were available to them, 
i.e. there was little opportunity for size selection. 
Consequently, the mean size of fish harvested could 
remain relatively stable under increasing levels of fish- 
ing pressure until there were no more fish left to catch. 
Indications that fishing pressure was affecting the 
population included 1) decreases in maximum size 
of fish over a 9-year period, 2) the absence of very 
old fish in the Samoan population compared with the 
GBR population, as might be expected in a fished 
population, and 3) a possible decrease in CPUE. 
These points, too, are less than compelling. First, the 
Wass, R. 1981. The shoreline fishery of American Samoa, 
past and present. In J. Munro (ed. ), Marine and coastal pro- 
cesses in the Pacific: ecological aspects of coastal zone manage- 
ment: proceedings of the UNESCO seminar at Motupore Island 
Research Center, 1980, p. 51-63. United Nations Education, 
Scientific and Cultural Organization, Paris. 
