CONTRIBUTION TO THE POPULATION DYNAMICS OF ATLANTIC 

 ALBACORE WITH COMMENTS ON POTENTIAL YIELDS' 



Grant L. Beardsley- 



ABSTRACT 



Length-frequency data on Atlantic albacore from the Bay of Biscay surface fishery and the Atlantic 

 longline fishery were analyzed. Lengths at age were estimated and the von Bertalanffy growth param- 

 eters wei-e calculated: K = 0.141, Loo = 140 cm, and tp = —1.63 years. Instantaneous rates were 

 computed on an annual basis. The total instantaneous mortality coefficient was estimated as 0.96 for 

 albacore in the Bay of Biscay fishery and 0.79 in the longline fishery. Analysis of catch and effort data 

 suggested that greater yields are available from the North and South Atlantic longline stocks though 

 stock identification in the South Atlantic is not clear. Estimates of population structure in the North 

 Atlantic were made by utilizing total instantaneous mortality rates of 0.50, 0.96, and 1.40 and an in- 

 stantaneous natural mortality rate of 0.23. The population based on a total mortality coefficient of 0.96 

 appeared to be the most reasonable. 



The albacore, Thunnus alalunga, has become in- 

 creasingly important to the Atlantic tuna fish- 

 eries in recent years. From 1956 to 1961 the 

 Japanese longline fishery in the Atlantic was 

 primarily directed at yellovvfin tuna, T. albacares, 

 but rapidly declining catch rates for yellowfin 

 soon forced a shift of fishing into primarily al- 

 bacore areas (Wise, 1968). As a result of de- 

 creased yellowfin catches and a corresponding 

 shift in fishing toward albacore, the average 

 number of albacore caught yearly by the Jap- 

 anese in the Atlantic increased from 228,000 in 

 the years 1956-61 to 1,332,857 in the years 1962- 

 68. The percentage of albacore in the combined 

 catch of albacore and yellowfin in the Atlantic 

 by the Japanese rose from an average of about 

 18.7^; in 1956-61 to 67.7% in 1962-68 

 (Figure 1). 



Since 1965 the Japanese have significantly cur- 

 tailed their longline fishing in the Atlantic. From 

 a high of almost 100 million hooks in 1965, they 

 set slightly over 30 million hooks in 1967 and 

 again in 1968. This decrease, however, has been 

 offset by the entry of China (Taiwan) and South 

 Korea into the fishery as well as small amounts 



' Contribution No. 203, National Marine Fisheries 

 Service, Southeast Fishery Center, Miami, Fla. 33149. 



- National Marine Fisheries Service, Southeast Fish- 

 ery Center, Miami, Fla. 33149. 



100 

 90- 

 80 

 70 



S 60- 



50- 

 ^ 40 

 30 

 20 



10 



-2 



percent albacore 

 no. albacore 



-f^ 



p 



o 



o 



Manuscript accepted June 1971. 



FISHERY BULLETIN: VOL, 69. NO, 4, 1971 



1 I I — 1 — I — I — I — 1 — I — I — I — r 

 1956 '60 65 68 



YEAR 



Figure 1. — Total number of albacore caught and the 

 percentage of albacore in the combined yearly albacore- 

 yellowfin tuna catch by Japanese longliners in the At- 

 lantic Ocean, 1956 through 1968. 



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