O NUMBER OF FISH/10» 

 ■ METRIC TONS/10' 



Figure 41 Annual catches by Bay of Biscay fisheries for small and some medium 

 size bluefin tuna in hundreds of thousands of fish and in tlioasands of tons. 



run from late April through June. 

 Some of these were reversed at the 

 end of June and fished the "return" 

 (westward) run in July and August. 

 The Moroccan traps faced southwaid 

 and fished the "arrival" run, which 

 was northward in that locality, only 

 After the 1976 season it appeared 

 that, of all these traps, only one or 

 two located off the Spanish coast 

 would continue to operate 



These fisheries, and the biology 

 of the fish which supply them, have 

 been the subject of a great many in- 

 vestigations and scientific papers. 



There are two maxima in the 

 fishery, one near the middle of the 

 "arrival" run, and the other near the 

 middle of the "return" run Spawn- 

 ing is presumed to occur between 

 these maxima (Sella 1929a, 1929b; 

 Vilela 1960) Sella (1929b) provided 

 generalized diagrams showing the 

 variation of the catches with dates 

 and the movements of the fish in the 

 vicinity of the traps during the spawn- 

 ing cycle (Figure 47) 



For fish of the same length, those 

 taken in the "arrival" run average 

 about 15% heavier than those taken 

 in the "return" run (Rodriguez-Roda 

 1964b) (data from fish taken at 

 Barbate, 1956-1961) Vilela el al 

 (1960) found that females lost about 

 21 percent of their weight between 

 the two runs, when most of the spawn- 

 ing takes place, while males lo.st only 

 about 10 percent of their weight 



Length frequency data for the 

 Spanish fishery for the vears 1956- 

 1959, 1961 and 1963-1975 are pre- 

 sented (Figure 48) 'fhe catch con- 

 sisted mainly of medium and giant 



30 r 



fish, with small ones (ages 1-2) 

 significant in 1958 and 1959 only. 

 Medium sized bluefin were domi- 

 nant in 1957 and important in 

 1 956, 1 958, and 1 959. Since 1 960. 

 however, giants have constituted 

 over 70 percent of each year's 

 sample One year class, probably 

 that of 1954, dominated the 

 samples for the years 1963-1965 

 (Rodriguez-Roda 1969b). Length 

 frequency data are not available 

 for the Portuguese trap catches, 

 but the yearly catches for the years 

 1931-1972 (Vilela and Cadima 

 1961, Hamre and Tiews 1964, 

 Hamre et al 1966, 1968, 1971) 

 are shown in the size groupings 

 traditionally used in this fishery 

 (Figure 49) 



Fish of the "atuns" size were 

 usually dominant, but in three 

 years the cachorretas, nearlv the 

 same sizes as our "small" group, 

 considerably outnumbered them. 

 The.se fish were generally most 



20 - 



10 - 





 30 



7S 



o 



20 - 



10 - 







30 



20 - 



10 



150 

 Length (cm) 



200 



250 



Figure 42, Lengths of bluefin tuna captiued fi-om the Bay of Biscay ("+" on graph 

 means less than 5'Mi) 



43 



