FISHERY BULLETIN: VOL. 69, NO. 4 



Table 1. Using this method I obtained the fol- 

 lowing values of Z: 



Year class Z 



1964 (3 years old in 1967) 0.73 



1965 (3 years old in 1968) 1.04 



1966 (3 years old in 1969) 1.12 



The average total mortality coefficient over the 

 3 years was estimated to be 0.96. 



LONGLINE FISHERY 



A total mortality coefficient was calculated for 

 albacore in the longline fishery using a formula 

 derived by Beverton and Holt (1956): 



Z = K {L. 



L) 



L — Lr 



where L is the average length of the fish in the 

 catch that are as large as or larger than the first 

 fully recruited length, Lr. 



Using: L«, 

 K 

 L 



Lr 



then: 



140 cm 

 0.141 

 94.2 cm 

 86 cm 



0.79 



The total mortality coefficient is not incom- 

 patible with the average Bay of Biscay estimate 

 if we consider that the longline is probably rel- 

 atively inefficient compared with surface gear; 

 hence fishing mortality in the longline fishery 

 and consequently total mortality (assuming nat- 

 ural mortality stays nearly the same throughout 

 the life span of the fish) is probably less than in 

 the surface fishery. 



The albacore samples used to estimate mor- 

 tality in the longline fishery were taken over 

 several years from different areas in the Atlantic. 

 It is very likely, however, that the composite 

 length-frequency distribution in Figure 3 is not 

 a completely accurate picture of the length com- 

 position of albacore in the Atlantic. Size distri- 

 bution in the winter fishery, for example, is en- 



tirely diflS'erent from that in the summer fishery, 

 and suitable samples from each fishery would 

 have to be taken to ensure a representative pic- 

 ture over the entire ocean. 



YIELD ESTIMATES 



There are five major areas in the Atlantic 

 where longliners concentrate on albacore. I 

 have designated these areas A through E in 

 Figure 8 and for ease of discussion will sub- 

 sequently refer to these areas by their letter 

 designation. Areas A, B, C, and D were de- 

 scribed by Beardsley (1969) and Koto (1969) 

 as major fishing areas. Area E off the coast 

 of Argentina, Uruguay, and southern Brazil has 

 only recently developed into a relatively major 

 albacore fishing area. Of the four areas dis- 

 cussed by Beardsley and Koto, only area C has 

 shown a decline over the years in catch rate 

 (Figure 9). Areas A and D produce fish that 

 are relatively small for longline fish and pre- 

 sumably are recruits to the longline fishery. 

 Recent size data obtained from albacore landed 

 in Puerto Rico and caught in area E reveal that 

 small albacore are also a large part of the catch 

 in this area. 



60»W 



FiGiiRE 8. — The ma.ior lonKline fishing areas for albacore 

 in the Atlantic Ocean. 



850 



