BEARDSLEY: POPULATION DYNAMICS OF ATLANTIC ALBACORE 



? s s s s s 



lOliK lEKGIH ICM> 



Figure 2. — Albacore length-frequency distributions from 

 the Bay of Biscay surface fishery, 1967-70. Estimated 

 ages in years are shown above the histograms. 



>- 



Z 

 -; 4 



FORK LENGTH (CM) 



Figure 3. — Albacore length-frequency distribution from 

 the Atlantic longline fishery, several years combined. 

 Estimated ages in years are shown above the histograms. 



albacore occasionally appear in the Japanese live- 

 bait fishery in spring, and they assume that these 

 fish are approximately 1 year old. On this basis 

 they assign 2, 3, and 4 years of age to 55-, 65-, 

 and 76-cm albacore respectively in the United 

 States west coast fishery. Yoshida (1968) 

 studied age and growth of juvenile albacore 

 based on 35 specimens recovered from stomachs 

 of billfishes in the Pacific. He derived a hatch- 

 ing date of May 1 based on a regression analysis 

 of length of the juveniles against month of cap- 



ture and concluded that 1-year-old albacore are 

 approximately 38 cm standard length. Although 

 I have assigned a length of 44 cm to age-group 

 I, a more practical approach would probably be 

 to accept Le Gall's (1952) statement that 1-year- 

 old albacore are "less than 48 cm in length." 



Longline length frequencies were used to esti- 

 mate ages 5 and older (Figure 3). The assign- 

 ment of ages beyond age 5 is somewhat subjec- 

 tive. I assigned ages 7 and 8 to the modes ap- 

 pearing at 100 to 101 and 104 to 105 cm. Other 

 ages were assigned mostly by extrapolation. My 

 estimates agree in most cases with those made 

 for Pacific albacore by Otsu and Uchida (1963). 

 No attempt was made to assign ages beyond age 

 10 although undoubtedly some albacore in the 

 Atlantic live to be older than 10. 



The two modes which correspond to ages 3 and 

 4 in the longline samples (68-69 and 78-79 cm) 

 are located at a length of 3 to 6 cm greater than 

 the same age in the Bay of Biscay samples. Yang 

 (1970) stated that ring formation on albacore 

 scales occurred in February-March for North 

 Atlantic albacore. The Bay of Biscay samples 

 were taken in summer, and the albacore had 

 completed approximately a half year's growth. 

 Most 3- and 4-year-old albacore captured by 

 longliners are taken in winter when they are 

 first recruited to the fishery. These 3- and 4- 

 year-old fish are at the end of a year's growth 

 or just beginning a new year's growth, and the 

 disparity in the position of the modes between 

 the longline samples and the Bay of Biscay 

 samples represents growth during the period be- 

 tween the summer fishery and the winter fishery. 



GROWTH PARAMETERS 



I constructed a Walford line (Figure 4) using 

 the lengths at age from this study (Table 1) and 

 took the intercept of the 45° diagonal as an initial 

 trial value for L„ in the expression for growth 

 (von Bertalanfl'y, 1938): 



lege (L„ 



Lt) = logeL, 



KU — Kt. 



A best fit was obtained with L„ = 140 cm. K 

 was calculated as 0.141, and U was — 1.63 years. 

 Yang (1970) found L = 135 cm and K = 0.19 



847 



