218 
Fishery Bulletin 106(2) 
A Abundance 
o 
o 
n i i i — i — i — r 
-7 -6 -5 -4 -3 -2 -1 
0 1 
Lag (days) 
LL 
o 
o 
B Species richness 
0 . 4 — 
0 2 - 
- 0 . 2 - 
-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 
Lag (days) 
Figure 3 
Cross-correlation plots of the average nightly abundance (A) and species richness (B) for larvae sampled in crest and 
channel nets for flow-correccted data. These plots identify any significant delay between catch in the crest versus chan- 
nel nets. Lag refers to the number of days by which one of the data sets is offset from the other when the correlation is 
calculated; data sets are aligned for correlation on the same day at a lag of zero, and the crest net data leads the channel 
net data by one day for correlation at a lag of +1, etc. The cross-correlation function (CCF, correlation coefficient between 
the two data sets at each lag) is on the ordinate. Values of the CCF above and below zero represent positive and nega- 
tive correlations between net types; the horizontal lines above and below the abscissa indicate the upper and lower 95% 
confidence limits, respectively. 
corresponded to fewer numbers of species caught in 
full-moon periods. 
Discussion 
Crest nets caught greater numbers of individuals and 
species per deployment than channel nets and would 
therefore be an advantageous sampling tool to use in 
studies attempting to maximize the chance of catch- 
ing greater numbers of a certain species. However, the 
difference between net types was not solely due to the 
design of the net. The two net types were deployed at 
two different habitats. All larvae passing over the top of 
a small width of the reef crest were sampled as the reef 
slope forced them into a constrained water column. In 
contrast, in the mangrove channels, only the top meter 
of the water column was sampled and larvae were free 
to pass underneath the floating channel net. A compari- 
son of the suites of larvae caught in each habitat would 
provide information about their settlement preferences. 
Such a comparison could not be made in the present 
study because the difference in the amount of the water 
column sampled was not controlled. However, Shenker et 
al. (1993) reported poor catches in subsurface deployed 
channel nets, and this finding indicates that most larvae 
that are still in the water column as they pass through 
the mangrove channels behind the reef crest remain 
near the surface of the water. 
Lunar periodicity of arriving settlers has been well 
documented in some reef fish species; greatest recruit- 
ment usually occurs at the darkest phase of the moon 
(Victor, 1986; Thorrold et al., 1994; D’Alessandro et 
al., 2007). Rayleigh 2 tests on non-flow-corrected data 
showed that significantly more larvae were caught at 
the new moon in the present study. When the catch was 
standardized by volume of water filtered however, all 
lunar periods had similar numbers of individuals per 
unit of water volume and no periodicity existed. This 
finding indicates that water flow was greater during 
the dark moon periods (new and last quarter) than 
during bright moon periods (first quarter and full), and 
the greater water flow removed the correlation between 
the quantity of larvae caught and the lunar period. It 
appears there was approximately the same number of 
larval fish per unit of water volume throughout the 
lunar cycle; the increased flow around the new moon 
simply carried more of them into the nets. Alterna- 
