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Fishery Bulletin 96(4), 1 998 
age class 4 (sector 4). The minimum size corresponded 
to age class 0 in all sectors. 
Maximum size decreased during March-May (see 
Fig. 6, A and B). In June and July there was a pos- 
sible entry of newborn fish (65 cm) with the same 
birth size as that suggested by Compagno (1984). 
Mean size decreased during October-November. 
These changes in size distribution suggest a move- 
ment of the largest and mean-size shortfin mako 
sharks out of the study area. For an area just north 
of the one studied, Mejuto 2 showed a large increase 
in catch rate during the last quarter of the year, which 
could be attributed partially to entry of fish coming 
from our study area. 
Blue shark 
The abundance of this species in longline fishing has 
been mentioned by several authors (Bigelow and 
Schroeder, 1948; De Metrio et al., 1984; Munoz- 
Chapuli, 1985; Stevens, 1990; Mejuto 2 ). In the 
present study the proportion of blue sharks, com- 
pared with swordfish, was half that estimated by 
Garces and Rey ( 1983) for an area that included our 
five sectors. However, it was greater than the pro- 
portion obtained by Rey and Alot (1984) in the west- 
ern Mediterranean and very similar to that calcu- 
lated by Mejuto 2 for the area just north of our study 
region. The number of fish landed increased north- 
ward and was greater than the number estimated 
by De Metrio et al. (1984) in the Mediterranean. 
The temporal distribution of fish was also differ- 
ent for the Mediterranean (De Metrio et al., 1984) 
and for the northeastern Atlantic (Mejuto 2 ). As in 
the case of shortfin mako sharks, the highest catch 
rates correlated with reductions in swordfish catch 
rates, i.e. April and September (Fig. 10). 
The overall sex ratio (1 male:0.71 females) was 
inverse to that found by Rey and Alot (1984) in the 
Mediterranean. The latitudinal distribution of sexes 
was inverse to that estimated by Stevens (1990) off 
southwest Great Britain and Portugal and to that 
presented by Nakano et al. (1985) in a similar lati- 
tude in the central north Pacific. 
Using Pratt (1979) and Cailliet et al’s. (1983) age 
estimate, we found that frequency distribution of fish 
by size of landings in sector 1 showed that mature 
males were more abundant, whereas in the other 
sectors a greater proportion of immature fish were 
observed. 
Bigeye thresher shark 
The relatively frequent occurrence of this species 
noted by Munoz-Chapuli (1985) contrasted with the 
low numbers observed in our study, with the low 
65 90 115 140 165 190 215 240 
Fork length (cm) 
Figure 1 1 
Proportion of male shortfin mako sharks in landings by size group (grouped by 5 cm FL). 
