Contouring was done by computer, assign- 

 ing the catch-per-unit-of-effort value for each 

 square to a point in the geometric center of 

 the square. Although our charts (Figures 

 1 and 4-13) are a square projection, the 

 "squares" are, of course, not square. One 

 degree of longitude is approximately equal 

 to 60.722 nautical miles x cosine latitude. 



100? 80° 60" 40° 20° 0° 20° 



100° 80° 60° 40° 



0° 20° 



Figure 1. — Divisions of the Atlantic Ocean. 



The program used for contouring could 

 not effectively distinguish squares with no 

 data from those with values of zero, and it 

 contoured squares which are part water as 

 if they were all water. For these reasons we 

 edited the computer plots, terminating all 

 contours at the coast and a half-square be- 

 fore the edge of the data field. 



For the sake of clarity and simplicity the 

 contours in Figures 4-13 are usually drawn 

 at the levels of 2, 4, and 6, and the number 

 of hooks is varied appropriately by orders 

 of magnitude: 



Fish per 100 hooks - 

 Fish per 1,000 hooks - 



Fish per 10,000 hooks ■ 



Albacore 



Yellowfin 



Bigeye 



White marlin 



Blue marlin 



Sailfish and spearfish 



Bluefin 



Swordfish 



Black marlin 



Skipjack 



The level of 4 (per 100 or 1,000 or 10,000 

 hooks) is shown by a dashed line. In cases 

 where the catch rates exceeded 6 (per 100, 

 etc., hooks) in significant amounts, the fact 

 is noted in the explanatory text for each 

 species. Black marlin and skipjack are ex- 

 ceptions — their apparent abundance is so 

 low that contours are drawn only at the 

 single level of 1 per 10,000 hooks, roughly 

 equivalent to comparison of presence vs. ab- 

 sence. 



INTERPRETATION OF 

 CONTOURS 



The various species have shown differing 

 apparent responses to exploitation, and these 

 responses, of course, affect the mean abundance 

 values. (Wise, 1968; Wise and Fox, 1969; 

 Wise and LeGuen, 1969.) For this reason, in 

 Figure 2, we show for each species the annual 



YEAR 



YEAR 



Figure 2. — Catch per thousand hooks, 1956-68, various 

 tunas and billfishes in selected areas (see text) in 

 the Atlantic Ocean. 



