The shaded regions include the areas in 

 which we have reasonable confidence in the 

 contours, with confidence increasing as the 

 amount of fishing included increases. Contour 

 lines outside of the shaded areas are related 

 to very small amounts of fishing and should 

 be interpreted with caution, especially where 

 there are isolated peaks of high apparent 

 abundance. 



In evaluating the amount of confidence to 

 be placed in the contour lines, however, we 

 feel that giving consideration only to the 

 amount of fishing is oversimplification. When 

 a concentration repeats in more than one 

 quarter, or when it appears to be coherent 

 with one or more others appearing in other 

 quarters, it can often be given more credence 

 than that based simply on the amount of 

 fishing. The ideal, of course, would be to have 

 the fishing uniformly distributed over the 

 ocean. An alternative would be to apply an 

 objective statistical procedure to reject catch- 

 per-unit-of-effort values derived from amounts 

 of fishing below a critical value. The first 

 is impossible and the second probably not 

 practical, so a certain amount of subjectivity 

 must remain in the interpretation of the con- 

 tours. 



BLUEFIN AND 

 SOUTHERN BLUEFIN TUNAS 



The published Japanese statistics did not 

 separate the bluefin and the southern bluefin 

 previous to 1966. In the period 1966-68 about 

 30% of the total catch of both species was 

 southern bluefin, but less than 100 southern 

 bluefin were caught north of lat 20 °S. About 

 75% of the catch south of lat 20 °S was report- 

 ed as southern bluefin. We shall generally 

 consider concentrations north of lat 20 °S as 

 bluefin and concentrations south of 20 °S as 

 southern bluefin. 



Figure 4 shows the distribution of catches 

 of bluefin for the four quarters of the year. 

 The most consistent features are a concentra- 

 tion of bluefin off the easternmost part of 

 South America all year round and another, 

 probably of bluefin and southern bluefin (Tal- 

 bot and Penrith, 1963), on or near the African 

 coast south of lat 20 °S, in every quarter but 



the first. There is a concentration in the first 

 quarter just north of lat 20°S; it appears 

 probable that this is related to the African 

 coastal group. 



There is a concentration around Cuba and 

 Puerto Rico in the first quarter, extending 

 into the northern Gulf of Mexico and along 

 the east coast of North America in the second 

 quarter. It is off the northeastern United 

 States and Newfoundland in the third quarter 

 and extends southward in open water from 

 Nova Scotia and Newfoundland in the fourth 

 quarter. This pattern is consistent with a 

 migration pattern outlined by Rivas (1955). 

 The migration hypothesis for northwest At- 

 lantic bluefin was unsupported by any direct 

 evidence for many years, but recently long- 

 liners off New England and Nova Scotia 

 caught two bluefin tagged in the Bahamas 

 (F. J. Mather, III, personal communication). 



In the first through third quarters there 

 are "spots" of bluefin extending eastward 

 from the concentrations mentioned above, 

 and in the fourth quarter there is a large 

 concentration centered on long 30 °W in the 

 North Atlantic. These distributions may be 

 related to the irregular transatlantic migra- 

 tions of bluefin discussed by Mather (1969). 



Although there are relatively important 

 fisheries for bluefin on the European coast, 

 in the Mediterranean, and on the northwest 

 coast of Africa, nearly all of the large con- 

 centrations in Figure 4 occur west of long 

 20°W. 



The apparent abundance of bluefin during 

 the 1956-68 period increased from very low 

 levels in the early years to a peak in 1962-66, 

 then returned to low levels (Figure 2). A 

 similar cycle may be seen in the purse-seine 

 catches off New England (Wise, Beardsley, 

 and Mather, 1971). While great changes in 

 catch-per-unit-of-effort values with time make 

 any absolute values questionable, average 

 catches per unit of effort in the concentrations 

 shown run over 50 per 10,000 hooks in the 

 first quarter and over 100 per 10,000 hooks 

 in the second quarter. 



ALBACORE 



The most obvious feature in the distribution 

 of albacore for the four quarters of the year, 



10 



