Poisson et al.: Effects of lunar cycle and fishing operations on longline catches 
269 
130 km/h (Lee et al., 2009) and Fritsches et al. (2005) 
demonstrated that their large eyes and pupils are ide- 
ally adapted to detect rapid movements in dim light. 
Swordfish rely on visual cues at small scales (meters) 
and ambient light conditions are likely to be a major 
factor influencing feeding behavior. 
There is strong anecdotal information from captains 
who target large pelagic fish that the lunar phase af- 
fects fishing success for swordfish and other pelagic 
fish. The effect of the lunar cycle on swordfish catch- 
ability has been investigated in longline (Bigelow et al., 
1999; Neves Dos Santos and Garcia, 2005; Damalas et 
al., 2007) and driftnet fisheries (Di Natale and Manga- 
no, 1995), but the results obtained are not directly 
comparable because they were conducted in differ- 
ent areas and fisheries. Generalized additive models 
(GAMs) have been used to examine the relative in- 
fluence of environmental conditions and operational 
factors on pelagic longline catch rates (Bigelow et al., 
1999; Walsh and Kleiber, 2001; Tserpes et al., 2008). 
In the case of the Reunion Island longline fishery, 
Guyomard et al. (2004) demonstrated significant effects 
(among others) of geostrophic currents generated by 
sea level anomalies (SLA) and lunar day on swordfish 
catch and catch per unit of effort (CPUE, number of 
fish per 1000 hooks). 
I n 1991, the first swordfish longliner began operating 
from Reunion Island, a French overseas territory in the 
southwestern Indian Ocean (21°5'S lat., 53°28'E long.), 
Two main factors promoted the development of this 
fishery: 1) the success of the Asian fleet that was based 
at Reunion Island and 2) a new tax regulation, offering 
exemption for certain investments in French overseas 
territory, which encouraged French fishing companies 
to come to Reunion Island. The annual average catch 
in the Reunion Island longline fishery during the years 
1996-2000 was 2670 metric tons (t) and the composi- 
tion by weight was 1730 t (65%) of swordfish (Xiphias 
gladius), 320 t (12%) of albacore ( Thunnus alalunga), 
270 t (10%) of yellowfin tuna (T. albacares), 130 t (5%) 
of bigeye tuna (T. obesus ), 90 t (3%) of billfish (Indo- 
Pacific black marlin [ Makaira indica ], Indo-Pacific blue 
marlin [M. mazara], shortbill spearfish [ Tetrapturus 
angustirostri s], and Indo-Pacific sailfish [Istiophorus 
platypterus]), 60 t (2%) of sharks, and 70 t (3%) of other 
species. 
The main goal of the current study was to investi- 
gate the performance of the domestic longline fishery 
at Reunion Island with regard to several variables to 
determine whether lunar periodicity affected the catch 
of pelagic species. A three-year logbook data series 
(1998-2000) was used. In addition, data were aug- 
mented by deploying time-depth recorders (TDRs) and 
hook-time recorders on a number of commercial longline 
sets. Information on capture time from hook timers 
allowed us to investigate the survival of large pelagic 
fish on longlines. Hourly catch rates were correlated 
with lunar illumination but also with the tidal phase 
which could be considered as an indicator of induced 
local currents. 
Finally, to test the assumption that feeding behavior 
of large pelagic fish was predicated on vision (sword- 
fish can differentiate between blue-green wavelengths 
[Fritsches et al., 2005]), we investigated whether green 
chemical lightsticks influenced catch rates and species 
composition. With the combined results for catch rates 
and species composition, we comment on the possibili- 
ties of modifying fishing operations and strategy 1) to 
reduce operational costs during fishing trips, 2) to re- 
duce loss of target fish at sea, and 3) to reduce bycatch 
mortality in accordance with the United Nations guide- 
lines for responsible fisheries (FAO, 2003). 
Materials and methods 
Operational characteristics of the domestic longline fleet 
The Reunion Island swordfish longline fishery is a sur- 
face fishery. An adapted “American style” gear is used, 
where the monofilament mainline (3.5-4 mm in diam- 
eter) longline is set at dusk and fished during the night. 
The mainline was deployed from a hydraulically powered 
spool over the stern and fishing depth was controlled 
by adjusting branchline (~20 m) and floatline lengths 
(~10-90m), distance between buoys (~50 m), number 
of hooks between floats (6-10 hooks), and vessel speed 
(Fig. 1). In strong currents, lead weights can also be 
added to branchlines to control mainline depth. The 
fishery uses J hooks (size 8/0 or 9/0) baited with squid 
(Illex spp.) and green chemical lightsticks were attached 
~1 m above the hook on every third branchline. 
The domestic longline fleet can be categorized by 
two vessel sizes (classes): a small-medium boat class 
(vessels <16 m), and a large boat class (vessels >16 
m). The fishery underwent dramatic changes between 
1992 and 2000 expanding from 5 to 23 active small- 
medium boats and from zero to 9 large boats, the 
latter with a peak of 14 in 1998. No longliners were 
authorized to fish within a zone of 30 nautical miles 
(~55 km) from Reunion Island in order to avoid con- 
flicts with the artisanal tuna fishery. Thus, these 
vessels explored new fishing areas within and beyond 
the French Exclusive Economic Zone (EEZ) (Fig. 2). 
The number of days at sea varied according to ves- 
sel size, vessel capacity, and weather conditions. The 
smallest boats stayed at sea 2-3 days, medium-size 
vessels generally stayed 6-8 days; whereas some of 
the largest vessels stayed at sea for up to 30 days. The 
large boats gradually expanded to fishing grounds to 
the west and southwest of Reunion Island within the 
EEZ in association with deep seamounts and sea sur- 
face temperature (SST) fronts (Fig. 2; area C) and to 
the Mozambique Channel (area B) and to Seychelles 
Island waters in 1997 and 1998 (area A). A decline of 
large boats from the fleet brought notable changes; 
therefore catches in 1999 and in 2000 were taken 
mainly around Reunion Island between 20 s and 25 9 S 
lat. and 50°-60°E long. Only a few vessels ventured 
far from Reunion Island in 2000. Table 1 summarizes 
