Poisson et al. : Effects of lunar cycle and fishing operations on longline catches 
273 
during the last days of the last quarter and reached 
the lowest values around the full moon phase (Fig. 4B). 
Moreover, CPUE decreased as tidal amplitude increased. 
Large confidence intervals around the mean CPUE per- 
taining to the new moon indicated a higher variability 
in fishing performance during this phase. The lowest 
CPUE was recorded between the 14 th and 17 th day of 
the lunar cycle during the full moon (which is charac- 
terized by the largest tidal ranges and maximum lunar 
illumination). 
Effect of lunar luminescence, tidal phase, 
and tidal velocity of local induced currents on catches 
Sample sizes of five species were considered adequate to 
conduct detailed analyses of lunar-related variables on 
a fine scale, although 15 species and 2 broader species 
groups were identified in the catches (Table 2). Swordfish 
were caught rapidly after the gear was set (Fig. 5) and 
during days characterized by weak lunar illumination 
because most of the individuals were confined in an area 
corresponding simultaneously to the negative part of 
both axes (Fig. 6). The occurrence of swordfish on the 
negative side of the first axis and mainly on the negative 
axis of the second axis indicates that swordfish were 
caught during low tides and to a lesser extent during 
flood tides characterized by a low current. These results 
reinforce earlier conclusions obtained at a large scale, 
although the results from the experimental data were 
weaker than the data from logbooks. 
As with swordfish, bigeye tuna are likely to be caught 
rapidly after the gear is set during periods of weak lu- 
nar illumination (Figs. 5 and 6). Bigeye tuna and blue 
shark exhibited an opposite distribution on the second 
axis, which indicated that blue sharks were caught late 
during the soak time of the longline set and when lumi- 
nescence was minimal. The limited number of albacore 
and yellowfin caught in the experimental data may have 
restricted the statistical analysis. No particular favora- 
ble or unfavorable conditions were identified for albacore 
on a daily scale (Fig. 6), in contrast to the influence of 
lunar intensity observed on a monthly scale. 
Effect of chemical lightsticks 
A marginally significant influence of lightstick density 
on CPUE and catch composition was observed (permuta- 
tion tests, P<0.05); but the majority of the CPUE vari- 
ability was not correlated with lightstick density (93.6% 
for PCA and 91.3% for FCA, Table 3). 
Capture depths, times, and fish survival 
TDRs indicated that the deepest depth of the mainline 
was 110 m; most of the longlines were deployed between 
30 and 110 meters (Fig. 7); consequently most hooks 
fished between 50 and 130 meters. Hook timers indicated 
that the number of commercial species caught (swordfish 
and tunas) declined with soak time (i.e., with the time 
the gear was in the water [Fig. 5A] ) and indicated an 
Axis 2 
A between-group projection of (A) the species, and of (B) 
the lunar days of the month (represented as numbers 
between 1 to 30), on the first plane of the between- 
group centered principal component analysis (CPCA) 
conducted on catch per unit of effort of albacore (Alb, 
Thunnus alalunga)\ swordfish (Swo; Xiphias gladius ); 
bigeye tuna (Bet, Thunnus obesus ); yellowfin tuna (Yft, 
Thunnus albacares); sharks (Shk), and dolphinfish (Dol, 
Coryphaena hippurus). Scale box in the upper right 
corner of each plot indicates the limits for the first 
and second axes. 
opposite trend for five bycatch species (Fig. 5B). Blue 
marlin and dolphinfish were mostly caught after the 
longline had soaked for 8 hours or longer. In particular, 
pelagic stingrays, and sailfish to a lesser extent, were 
caught mostly during gear retrieval. In contrast, more 
than 60% of the sharks were caught within the initial 
seven hours of fishing. 
Fish survival at longline retrieval varied widely 
among species (Table 4). Survival was high for species 
such as dolphinfish and black marlin which strike the 
hooks mainly during retrieval. Over 40% of the main 
elasmobranch species (blue shark, oceanic whitetip. 
