Buencuerpo et al.: Pelagic sharks associated with the swordfish fishery 
683 
numbers noted by Moreno and Moron ( 1992a) in the 
same area, and with the low numbers noted by 
Stillwell and Casey (1976) in the northwestern At- 
lantic. The sexual segregation hypothesized by 
Munoz-Chapuli (1984) in this area, i.e. males dis- 
tributed northward and females southward, was op- 
posite that of our findings. Moreno and Moron ( 1992a) 
mentioned that most fish caught during the fall were 
pregnant females, whereas in this study mostly ma- 
ture males from the iongiine fishery and mostly fe- 
males from the gillnet fishery were recorded during 
the same period. 
Most males in all sectors were adults (>276 cm TL, 
Moreno and Moron, 1992a). Most females would be 
have been considered mature in every sector accord- 
ing to Gubanov’s (1979) first maturity size (>310 cm 
TL), but only in sector 5 according to Moreno and 
Moron’s ( 1992a) criteria (340 cm TL). The largest fish 
was recorded in sector 5, a 432-cm-TL female, in Sep- 
tember 1991, which, nevertheless, did not exceed the 
maximum for the species (460 cm TL, Nakamura, 
1935). 
Size distributions by month showed a greater pro- 
portion of immature males during the July-Septem- 
ber period, 'whereas mature fish predominated the 
rest of the year. During January- ••■June and October- 
December most females were around maturity size 
limit (300 cm TL, Gubanov, 1979). 
Most births occur during fall and winter accord- 
ing to Moreno and Moron (1992a), and as these au- 
thors have suggested, sector 5 could be a breeding 
area. A pregnant female was recorded in September 
1991, in sector 5, carrying only one pup. However, 
no newborn fish were recorded, according to birth 
sizes reported by Bigelow and Schroeder ( 1948), Bass 
et al. (1975), Gruber and Compagno (1981), and 
Moreno and Moron (1992a). 
Common thresher shark 
The scarcity of this species in the present study dis- 
agrees with observations of Munoz-Chapuli (1985). 
The relative abundance of common thresher sharks 
found in sector 5 was similar to that presented by 
Moreno et al. (1989) for the same area. The maxi- 
mum number during spring agreed with the num- 
ber observed in California (Cailliet and Bedford, 
1983) but did not coincide with the peak reported by 
Moreno et al. (1989) during fall in this area. 
The sex ratio for this species in the area studied ( 1 
male:2 females) differed greatly from estimates by 
Holts (1988) on the west coast of the United States 
(1 male:l female). Moreno et al. (1989) noted the 
absence of males in May, which suggests sexual seg- 
regation during the reproduction period. A mature 
male was recorded in May at 330 cm TL, which rep- 
resents the lower limit of maturity for males accord- 
ing to Cailliet et al. (1983). 
Only one female was recorded below size of first 
maturity (260 cm TL, established by Gubanov, 1972; 
Cailliet and Bedford, 1983; Cailliet et al., 1983). 
Moreno et al. (1989) pointed out the probable exist- 
ence of a breeding area close to the Strait of Gibraltar 
during spring time. The record of a 425-cm-TL preg- 
nant female, with four full-term pups in May, sup- 
ports this theory. 
Scalloped hammerhead shark 
According to sex and length data obtained from sec- 
tors 1, 3, and 5, the overall sex ratio (1 male:0.83 
females) differed from the ratio observed by Munoz- 
Chapuli (1984) in the same area (1 male:6 females). 
If we follow Compagno’s ( 1984) first maturity size 
criteria (256 cm TL for males, 304 cm TL for females), 
only 6% of males and 4% of females landed would be 
considered mature in our study area. Munoz-Chapuli 
(1984) observed many pregnant females in the area 
throughout the year, but the lowest size recorded in 
our study (114 cm TL) was much greater than birth 
size (50-60 cm TL, Compagno, 1984). Moreover, the 
lack of mature females contradicts the assessment 
that the study area is a breeding area, as suggested 
by Munoz-Chapuli ( 1985). 
Conclusions 
Sharks, because of their low reproduction rate and 
late sexual maturity, are extremely sensitive to fish- 
ing pressure (Holden, 1973, 1974, 1977). The vulner- 
ability of shark populations as bycatch of some tuna 
and tunalike fishing is comparable to that of marine 
mammals (Burke and Francis, 1990). In recent years 
several cases of overexploitation in shark fisheries 
(Cailliet and Bedford, 1983; Holts, 1988; Vas, 1990; 
Hanan et al., 1993) and the effect of other fishing 
activities (recreational fisheries, the routine proce- 
dure of discarding sharks after removal of fins) on 
shark populations (Casey and Hoey, 1985; Stevens, 
1992) has been described. 
A lack of fishery statistics about sharks is com- 
monplace all around the world. Du Buit ( 1989) com- 
mented on the complete absence of knowledge about 
most biological factors influencing shark populations 
off the coast of France and on the difficulty in sam- 
pling most of these migratory species. 
Our study shows the importance of shark landings 
in the Atlantic swordfish Iongiine fishery and points 
out the large number of immature fish involved. 
