Buencuerpo et al.: Pelagic sharks associated with the swordfish fishery 
669 
Proportions of swordfish and the five most com- 
mon shark species landed by longlines were signifi- 
cantly different (x 2 =5.41; df=20; P<0.001) in each 
sector (Table 3). The highest proportion of fish in all 
the sectors, except one (sector 1), was that of blue 
sharks, whereas the lowest proportion in all five sec- 
tors was that of the common thresher shark. Sword- 
fish occurred with decreasing proportion from south 
to north in the Atlantic sectors, reaching a minimum 
in the Mediterranean sector. Shortfin mako sharks 
steadily decreased from sector 1 to sector 4. The pro- 
portion of sharks, overall, was greater than the pro- 
portion of swordfish in all sectors, and sharks were 
included in at least 80% of the landings in all sec- 
Table 1 
Total number of fish sampled from 175 landings at the 
Algeciras (Cadiz) fish market and percentage by species 
from July 1991 to July 1992. 
Species 
Number 
Percentage 
Isurus oxyrinchus 
5947 
11.6 
Prionace glauca 
32,661 
63.7 
Alopias vulpinus 
52 
0.1 
Alopias superciliosus 
557 
1.1 
Sphyrna zygaena 
757 
1.4 
Other sharks 
224 
0.4 
Total sharks 
40,198 
78.5 
Xiphias gladius 
9990 
19.5 
Other bony fish 
1017 
2.0 
Total 
51,205 
100.0 
tors, where they were slightly greater in numbers 
than swordfish, except in sector 1. 
The proportional distribution of fish from gillnet 
landings was significantly different from that of fish 
from longline landings in the same sector <x 2 =2.97; 
df=5;P<0. 001) (Table 3). Gill nets were operated only 
in sector 5. Swordfish represented a much higher 
proportion in total gillnet landings than in longline 
landings; sharks represented only one third of total 
gillnet landings. The drop in the relative importance 
of sharks was due mainly to a much lower number of 
blue sharks in gillnet landings than in longline land- 
ings (8% compared with 82%). Bigeye thresher sharks 
slightly increased in landings (from 0.01% to 6%). 
The proportions of fish landed by longline differed 
significantly by month (x 2 =3.55; df=48; PcO.OOl) (A. 
vulpinus not considered) (Table 4), although blue 
shark was always the most predominant. Swordfish 
and shortfin mako sharks had the next highest pro- 
portions, whereas the other species never reached 
more than 5% of monthly catches. Sharks always 
accounted for more than 50% of the monthly catch, 
and more than 80% in 10 out the 13 months sampled. 
Proportions of fish in gillnet landings also differed 
significantly by month ( X 2 = 1.10; df=35; P<0.001) 
(March not considered) (Table 4). Swordfish had the 
highest proportion, except during the month of April. 
Blue sharks were taken in small proportions for most 
months (0-37%). The proportion of thresher sharks 
varied from month to month. Bigeye thresher sharks 
were taken at a maximum ( 10%) in August 1991 and 
July 1992; common thresher sharks also reached 10% 
in January 1992. The proportion of sharks exceeded 
Figure 2 
Species composition (% of fish) landed by the gillnet and longline fisheries operating in the eastern Atlantic Ocean and western 
Mediterranean Sea. 
