able error of +/-0. 12 between the state 

 of the tide and the catch of Barbate was 

 not significant. 



Salinities and dissolved oxygen 

 were also observed at Barbate by 

 Lozano Cabo. Although measurements 

 of both were taken from the surface 

 and at depths of 30 m or 35 m, he did 

 not study the correlation with the 

 catches. He had found no correlation 

 between salinity and catch at the Los 

 Cenizosos trap in Morocco. Salinities 

 at Barbate fluctuated between 35.39 o/ 

 GO and 35.53 o/oo at 35 m. Dissolved 

 oxygen levels were abnormally high 

 varying from 6.9 to 8. 1 cc/l at the sur- 

 face and 5.0 to 9.0 cc/l at 30 m. 



Rodriguez- Roda (1963, 1965, 

 1969c, 1970a, 1970b) collected envi- 

 ronmental data at the Barbate trap from 

 1961 to 1969, and discussed their pos- 

 sible relationships to its catches and the 

 movements of the maturing and post- 

 spawning bluefm tuna. His 1963 publi- 

 cation presented monthly values of the 

 temperatures, phosphate production, 

 and salinity, of the water at various 

 depths from the surface to 30 m, and its 

 transparency and optical absorption. 



Rodriguez-Roda (1969c) pre- 

 sented the mean temperatures at 1 m 

 intervals from the surface to 30 m in 

 the Barbate trap in August 1967. 

 Rodriguez-Roda ( 1 970a) collected daily 

 temperature measurements of the wa- 

 ter temperature at 10 m intervals from 

 the surface to 30 m for the months of 

 May through August 1968. He com- 

 pared the weekly averages of these tem- 

 peratures graphically with the corre- 

 sponding numbers of tuna caught in 

 the trap. He (1970b) collected corre- 

 sponding data and presented a similar 

 graphical comparison for the same pe- 

 riod in 1969. In that year he also mea- 

 sured the transparency of the water each 

 day, and he compared these values 

 graphically with the daily catch of the 

 trap in numbers of tuna. 



The temperature during the most 

 productive months. May to July in 1 96 1 

 and 1962, ranged from I8.0°C to 

 2 1 .4°C at the surface and 1 6.5°C to 1 8° 

 C at a depth of 30 m. During the "ar- 

 rival" run in May and June 1968, the 

 highest catches occurred with mean 

 surface temperatures of I7.2°C to 

 18.9°C and temperatures of I6.6°C to 

 17.6°C at 30 m. The best catches dur- 



ing the 1 969 arrival run were taken in a 

 week with mean temperatures of about 

 1 8°C at the surface and 1 6°C at 30 m. 

 During the "return" period in July and 

 August 1 968, the best catches took place 

 with temperatures of I9.5°C to 19.9°C 

 at the surface and I6.3°C at 30 m. In 

 1969, the best "return" catches were 

 taken with mean surface temperatures 

 of 21.0°C to 22.5°C, and temperatures 

 of 1 8.5°C to 20.2°C at 30 m. Rodriguez- 

 Roda noted (1969a), that the August 

 temperatures in 1961, 1962 and 1967 

 were about the same, and that the total 

 production of the Spanish Atlantic traps 

 in those years did not vary greatly. In 

 his 1 970b publication, he obser\ ed that 

 the catch of these traps was greater in 

 1 969, when the water was wanner, than 

 in 1968. Rodriguez-Roda (1971) con- 

 cluded that the maturing "arrival" pe- 

 riod begins at temperatures of 16°C to 

 1 7°C, and is most productive at tem- 

 peratures of 18°C in the upper 10 

 meters, 17°Cat20mand 16°Cat30m. 

 In the post-spawning "return" period, 

 optimum temperatures are 20°C to 2 1 °C 

 in the upper 10 m and I9°C at 30 m. 



The average salinities during the 

 monthsofMay, June and July in 1961 

 and 1962 varied from 35.88 o/oo to 

 36.34 o/oo at the surface and 36.01 o/ 

 00 to 36.21 o/oo at 30 m (Rodriguez- 

 Roda 1963). 



The transparency of the water 

 ranged from 1 1 m to 2 1 m in May and 

 June of 1961 and 1962, and from 2 m 

 to 25 m in May-August 1969, 

 (Rodriguez-Roda 1963, 1970b). The 

 author found a high positive correla- 

 tion, during intensive periods of the 

 fishery, between the transparency and 

 the catches of the trap. 



Phosphate production in May, June 

 and July, the months of ma.ximum tuna 

 catches, varied from 0.54 to 0.59 mg/l 

 at the surface. 



Chlorophyll production was gen- 

 erally greater in the cold months than 

 the warm ones, with a large maximum 

 in October and lesser ones in January' 

 and April. 



Zooplankton was predominant in 

 the wami months, although undergo- 

 ing many variations during the year, 

 due to the influences of Atlantic wa- 

 ters. 



Rodriguez-Roda ( 1 963) concluded 

 that the Barbate area, in regard to its 



oceanography and the plankton in gen- 

 eral, could be said to be under the influ- 

 ence of Atlantic waters, especially in 

 its surface layers. 



d. Morocco 



Lozano Cabo (1957, 1958, 1970) 

 conducted thorough studies of the en- 

 vironment at the Los Cenizosos trap, 

 north of Larache, Morocco. Our ac- 

 count generally follows his 1970 sum- 

 mary, with some details added from 

 the earlier reports. 



The water temperature varied from 

 1 7°C to 22°C at the surface, from 1 5°C 

 to 20°C at 15 m, and from 14°C to 

 1 8°C at 35 m. The correlation between 

 the surface temperature and the num- 

 bers of flsh caught was negative (-0.72 

 +/-0.06). Fish were caught at tempera- 

 tures between 17°C and 21°C, but 

 mainly between l8°Cand 19.7°C. 



The transparency of the water 

 ranged from 8 m to 19 m, with an 

 average value of 13.7 m. A high posi- 

 tive correlation, + 0.59 +/-0.08, existed 

 between the transparency and the num- 

 bers of flsh caught in the trap. The 

 catches were poor when the franspar- 

 ency was less than 13 m and good 

 when it was over 1 5 ni, especially at 1 5 

 m to 16 m. 



The salinities were between 36.00 

 o/oo and 36.34 o/oo at the surface, 

 36. 1 1 o/oo and 36.33 o/oo at 1 5 m, and 

 36.06 o/oo and 36 25 o/oo at 35 m. The 

 correlation between surface salinity and 

 the numbers of tuna caught in the trap.- 

 0.078 +/-0.13, was not significant. 



Likewise, no correlation was found 

 between the height of the tide (above 

 the daily low water level) and the num- 

 ber of tuna caught, even though the 

 captains thought that the tides strongly 

 influenced the catches. There was a 

 clear relationship, however, between 

 the velocity of the tidal currents and the 

 presence of tuna. Good catches coin- 

 cided with tides of large amplitude, 

 during which the coastal currents were 

 stronger and farther from shore. 



The dissolved oxygen content var- 

 ied from 5.9 to 7.9 cc/l at the surface, 

 from 5.7 to 7.9 cc/l at 15 m, and from 

 5.5 to 7.7 cc/l at 30 m. 



Alone le ( 1 964. 1 969) developed a 

 hypothesis on the migrations and 

 spawning of bluefln tuna, and the in- 

 fluences of water temperature upon 



90 



