as shown in Figure 5, is the separated northern 

 and southern distribution of the species, with 

 very low catch rates between about lat 15 °N 

 and5°S. 



Beardsley (1969) and Koto (1969) both 

 studied distribution of albacore in the At- 

 lantic on the basis of longline catch and 

 effort. Their analyses were based on shorter 

 series of data than we have used — Beardsley 

 used 9 years, 1957-65, while Koto used 5 years, 

 1961-65. Both agreed on generally east-west 

 seasonal migrations within both the northern 

 and the southern groups of albacore, with the 

 group of small fish located off extreme south- 

 west Africa interchanging with Indian Ocean 

 populations. 



Highest average catch rates occur off south- 

 west Africa — up to 10 fish per 100 hooks in 

 the first and third quarters and up to 17 fish 

 per 100 hooks in the second quarter. In other 

 areas, highest average catch rates almost 

 never are above 7 per 100 hooks. 



The almost complete absence of albacore 

 from the Gulf of Mexico, although not ap- 

 parent in Figure 5, is of some ecological 

 interest. Almost 11 million albacore were 

 caught in the Atlantic by longliners during 

 1956-68, but only 0.02% were caught in the 

 Gulf of Mexico (GM in Figure 1). The two 

 poorest areas for albacore outside of the Gulf 

 of Mexico, the CV and GG areas of Figure 1, 

 yielded 2.4 and 3.1 fish per 1,000 hooks (total 

 catch divided by the total effort for the 13 

 years), but the same figure for the Gulf of 

 Mexico (GM) was only 0.5 per 1,000 hooks. 



Also not shown on Figure 5 is the large 

 shallow concentration of albacore in the Bay 

 of Biscay from about June to October or 

 November of each year. While the longliners 

 fish little or none east of long 20 °W, north of 

 lat 20 °N (Figure 3), catches of more than 

 30,000 metric tons of albacore (roughly half 

 of the total Atlantic catch) are taken annual- 

 ly by French and Spanish fishermen with live 

 bait and by trolling. 



BIGEYE TUNA 



The distribution of bigeye is shown for the 

 four quarters of the year in Figure 6. Two 

 large concentrations are evident off the coast 

 of west Africa, separated at or near the 



equator, changing their shapes and bound- 

 aries with the seasons. The northern con- 

 centration is not defined at its northern edge 

 in any quarter except the third, and may ex- 

 tend all of the way across the Atlantic at 

 about lat 35°-40°N in every quarter except 

 the second. 



These distributions are different in many 

 respects from those outlined by Sakamoto 

 (1967) — the differences may be due to the 

 fact that Sakamoto used data only for 3 years, 

 1962-64. 



The apparently anomalous minor concentra- 

 tion of bigeye along the east coast of southern 

 Mexico and Central America in all four 

 quarters may be due to misidentification by 

 the fishermen of large blackfin tuna (T. at- 

 lanticus). 



Average catches inside the contour of 6 

 fish per 1,000 hooks reach over 30 fish per 

 1,000 hooks in some cases along the southern 

 African coast in the last two quarters, and 

 near this level in the northern concentration 

 in the first two quarters. 



YELLOWFIN TUNA 



Concentrations of yellowfin tuna are almost 

 entirely confined to tropical waters between 

 lat 20°N and 10°S, except for low or small 

 concentrations in the northwest Atlantic in 

 the third and fourth quarters and some con- 

 centrations in the Gulf of Mexico in all four 

 quarters (Figure 7). 



Wise and Le Guen (1969), among others, 

 have hypothesized that there may be eastern 

 and western populations of yellowfin in the 

 tropical Atlantic. There is some evidence in 

 Figure 7 of such a division, but the dividing 

 line could be placed at about long 70 °W, con- 

 siderably farther west than suggested by Wise 

 and Le Guen. 



The catch per unit of effort of yellowfin 

 has dropped markedly and steadily from 9 or 

 10 fish per 100 hooks in the first three years 

 of the fishery to less than 2 fish per 100 hooks 

 in 1964-68 (Figure 2) so that absolute values 

 must be interpreted with considerable caution. 

 The highest average value is nearly 19 fish 

 per 100 hooks in the western Gulf of Mexico 

 in the first quarter and nearly 12 fish per 

 100 hooks occur on the north coast of South 



13 



