598 



Fishery Bulletin 93(3). 1995 



due to the small variance of the recorded values 

 rather than to a morphometric discrimination be- 

 tween sexes. This can be seen by solving the equa- 

 tions for different spine-radius values. For example, 

 the computed LJFL values for a spine radius of 2 

 mm are: 1) 95.73 for males and 96.47 cm for females 

 from the linear method; and 2) 99.29 for males and 

 99.98 for females from the nonlinear method. 



The LJFL at the end of each year of life was 

 backcalculated for each individual and these lengths 

 were averaged for males and females separately to 

 obtain mean back-calculated lengths at age. These 

 generally agreed with lengths at age predicted by 

 the growth models and show that females grow faster 

 than males after an estimated age of 3 years (Table 3). 



Discussion 



Swordfish anal-fin spines have been used previously 

 for ageing Atlantic swordfish (Berkeley and Houde, 



1983). Ehrhardt (1992) attempted to validate the 

 method by means of marginal increment analysis and 

 reported that growth bands 1 to 4 were deposited 

 annually during the winter months. Results of mar- 

 ginal increment analysis of the present study dem- 

 onstrated that growth bands for fish 2 to 5 years of 

 age are deposited annually. In both the previous 

 cases, marginal increment analysis was successful 

 in showing the seasonality of band deposition; how- 

 ever, although these results partially validate the 

 method, it cannot be considered successful until all 

 reported ages of each population are validated 

 (Beamish and McFarlane, 1983). Marginal increment 

 analysis has also been successful in elucidating the 

 time of annulus formation in dorsal spines of 

 Tandanus tandanus (Davis, 1977). It is unlikely, how- 

 ever, that application of marginal increment analy- 

 sis to older ages, in which spine growth is consider- 

 ably reduced, would show any seasonality in band 

 deposition. In general, validation of ages of older fish 

 requires either a mark-recapture study or the iden- 



