Poisson et al.: Effects of lunar cycle and fishing operations on longline catches 
277 
Tide phase Capture time 
A 
•la 
■1b 
■2 
■2d 
c 
■Id 
■1c 
*2b 
■2a 
Moon luminescence 
U 
CO 
■ 
■3a 
3b 
1.5 
1.8 ^ 1.3 
-0.95 
Xiphias gladius Thunnus alalunga Thunnus albacares 
B 
■ ■ " ■ 
m a 
a 
■ ■ ■ ■■ 
■ * * . 
■ *1 
.■ 
■ . 
■ 
a " a a.“ f 
■» 
/ 1.7 N 
-1.6 ^ 1.2 
\ -1.1 / 
A) 
<is 2 
— Axis 1 
’ . ’ 
■" • . 
Thunnus obesus Prionace glauca 
Figure 6 
(A) Projection of the modalities for each factor on all species combined, and 
(B) the projection of individual fish stratified by species on the first axis 
of the multiple correspondence analyses (MCA). Description of the index 
modalities: “tide phase” la=ebb; lb=high, lc=flood, and ld=low; “capture 
time” 2a=0-4 h, 2b = 4-7 h, 2c=7-10 h, and 2d=>10 h; “moon luminescence 
index” 3a = low, 3b=high, and 3c = dark 
tracted by offal and spent bait discarded during the 
haul but also by the distress signals of captured fish 
(Myrberg et al., 1969) 
Our results indicate that swordfish and bigeye tuna 
exhibit active predation when lunar illumination is 
weak. These results are consistent with the findings 
of Fristches et al. (2005), who showed that retinas of 
swordfish and bigeye tuna provide visual acuity and 
sensitivity to blue-green light and thus these apex pred- 
ators are efficient visual hunters in dim light. 
We found that 60% to 80% of swordfish were caught 
after the gear soaked 4-6 hours and these results 
indicated a possible positive effect of bait freshness on 
the attractiveness of bait to swordfish and bigeye tuna. 
The effect of the chemical lightsticks on catch rate also 
decreased with time and as their glowing intensity 
waned. The role of the lightsticks is still not clear, al- 
though it is thought that they either attract predators 
to the bait or they attract small fish and squid (Hazin 
et al., 2005), or both, and as such, were considered as 
an important refinement of the longline gear. A signifi- 
cant but low association of lightstick density on CPUE 
was confirmed by our analyses. Bigelow et al. (1999) 
found that increasing the proportion of lightsticks from 
