DeMartini et al.: Age and growth of Xiphias gladius 



361 



Back-calculated lengths-at-age were 

 used to evaluate length versus age by us- 

 ing several versions of the von Bertalanffy 

 growth model, for a total 1292 fish (712 

 females, 580 males) >60 cm EFL. Less than 

 4% of all fin ray preparations were deemed 

 unreadable and not used. Age-group-0 

 fish (0.58 yr; 82.3 cm [females], 82.1 cm 

 [males]) were included in the model fits. 

 Male and female swordfish clearly grow in 

 length at different rates after age 1 (Ta- 

 ble 4; likelihood-ratio test; P<0.001; Table 

 5A). Furthermore, for central North Pa- 

 cific swordfish spanning the length range 

 of most fish in the commercial catch (60-cm 

 EFL as an average minimum), the stan- 

 dard three-parameter VBGF fit the length- 

 at-age data more efficiently than Richards' 

 generalized VBGF (likelihood-ratio test; 

 males: P>0.2, females: P=0.5; Table 5B). 

 Hence, the standard VBGF is the more 

 parsimonious growth model and should be 

 applied to the sexes separately for central 

 North Pacific swordfish of exploitable sizes 

 (Table 4; Fig 4). 



Three fish, whose ship-side, visually es- 

 timated weights were equivalent to lengths 

 of 88, 98, and 93 cm EFL when initially 

 tagged and released, were recaptured af- 

 ter 364, 610, and 1490 days at liberty and 

 had grown 38, 58, and 90 cm, respectively, 

 based on round weights at market (Uchi- 

 yama et al., 1998). The sex of none of these 

 fish was determined when they were tagged 



100 200 300 400 500 600 700 

 Number of presumed daily growth increments (DGI) 



800 



Figure 2 



Scatterplot and fitted relationship between the total cross-section 

 radius (iJ^,,, in mm) of the second ray of the first anal fin and the 

 number of daily growth increments (DGI; estimated age in presumed 

 days based on niicroincrement counts) on sagittae for the same young- 

 of-year and yearling swordfish (Xiphias gladius) (sexes pooled) caught 

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

 1993-97. The power equation, R^^^ = a DGI '', was used to model the 

 fitted relationship. The extended lines intercepting the x and v axes 

 represent the estimated radii at ages 365 and 730 days. Confidence 

 in the if,^( at age 730 days (3.5-3.6 mm) is low because of the poor 

 readability of DGIs at and beyond this age, for fish of either or both 

 sexes. 



