362 



Fishery Bulletin 105(3) 



140 



120 



e 100 



o 



6 



i 

 >. 



LU 



Predicted fit 



-A— EFL at 365 days 

 95% confidence bounds 



90 180 270 360 450 540 630 720 



Number of presumed daily growtti increments (DGI) 



Figure 3 



Fitted relationship between eye-to-fork length (EFL, in cm) and number 

 of daily growth increments (DGIs) on sagittae for young-of-year (age 

 + ) and yearling swordfish (Xiphias gladius) (sexes pooled) caught 

 in the region of the Hawaii-based pelagic longline fishery during 

 1993-97. A hyperbolic equation, EFL = (a DGI)l(b+DGI). provided 

 the best two-parameter relationship. The extended lines intercepting 

 the X and ,v axes represent the estimated EFL at age 365 days. 



5 6 7 

 Age (yr) 



10 11 12 



Figure 4 



Fitted curves (standard von Bertalanffy growth formula, VBGF) and 

 scatterplots of means of back-calculated EFL-at-age describing mean 

 length (cm)-at-age (yr) separately for male and female swordfish 

 (Xiphias gladius), caught in the region of the Hawaii-based pelagic 

 longline fishery during 1993-97. Scatterplots for the two sexes were 

 offset slightly for readability. EFL = eye-to-fork length.. 



or recaptured. If estimated length incre- 

 ments are related to a fit of the standard 

 VBGF (sexes pooled) for central North 

 Pacific swordfish, the growth trajectories 

 of these fish agreed reasonably well with 

 those expected for fish of their sizes at lib- 

 erty for the observed durations (Fig. 5). 



Discussion 



Verification and validation of age 



Our comparisons of ages based on annuli 

 in fin ray sections and DGIs in otoliths, 

 coupled with those of ray radii and oto- 

 lith ages, represent a novel approach to 

 verifying the age and growth of swordfish 

 and other species for which validation is 

 difficult. The good agreement we observed 

 between our estimates of size at age 365 

 days based on otoliths and of size at age 

 1 yr based on fin rays provides a strong 

 partial verification of our aging protocols 

 for young swordfish. Our detailed cross- 

 validation of fin ray annuli against otolith 

 DGIs has conclusively identified the location 

 of the first annulus on swordfish fin rays for 

 the first time. Marginal increment analysis 

 further corroborates that a single annulus 

 forms once each year in anal-fin rays and is 

 complete for swordfish through age 7 caught 

 in the central North Pacific by the end of the 

 spawning period in late summer (DeMar- 

 tini et al., 2000), when somatic condition is 

 lowest (Uchiyama et al., 1999). Others have 

 similarly observed that the time of annulus 

 formation occurs at the end of the growing 

 season for swordfish in the western North 

 Pacific (Sun et al., 2002) and eastern South 

 Pacific (CernaM, although other drains on 

 physiological condition, such as migration, 

 may be involved (Sun et al., 2002). We also 

 present final proof that basal cross sections 

 of fin rays underestimate ages as a result 

 of partial or complete resorption of the first 

 annulus, as first proposed by Berkeley and 

 Houde (1983) and subsequently observed by 

 Tserpes and Tsimenides (1995) and others. 

 Our comparison of age readings derived 

 from basal, dl2, and suture terminus cuts of 

 anal-fin rays demonstrates the equivalence 

 of the latter two types of ray cross sections. 



1 Cerna, F. J. 2006. Unpubl. data. Seccion 

 Edad y Crecimiento, Division de Investigacion 

 Pesquera, Institute de Fomento Pesquero, 

 Blanco 839, Valparaiso 5a Region, Chile. 



