HILL ET AL.: ANALYSIS OF GROWTH ZONES IN PACIFIC BLUE MARLIN 



increment number was extrapolated from these 

 data. 



Assessment of Ageing Techniques 



The usefulness of each hardpart for estimating 

 age in blue marlin was assessed by considering 

 ease of collection, hardpart gi'owth, precision of 

 age estimates, and the legibility of each hard- 

 part. 



To test the hypothesis that hardpart growth 

 was proportional to somatic growth of the ani- 

 mals, both UFL and W were modeled with AR, 

 DR, SW, and CD, categorized by sex. The signi- 

 ficance (two-tailed test) of r values was tested 

 (Schefler 1979). A paradigm of the ageing theory 

 is that the number of increments in or on a hard- 

 part increases with the gi"owth of the structure. 

 To test this assumption, AR, DR, SW, and CD 

 were modeled against increment counts for each 

 structure and the significance of the r values 

 was tested. 



Relative precision of age estimates and hard- 

 part legibility were determined by comparing 

 the variabihty of estimated ages between hard- 

 parts from the same fish. Direct comparisons of 

 age estimates from corresponding hardparts 

 (anal spines, dorsal spines, and sagittae) were 

 modeled with linear regression, and the slopes of 

 these regressions were tested to see if they 

 varied significantly from parity (Ho: beta = 1; 



Zar 1984). The significance of correlation coeffi- 

 cients (r) of the comparisons was tested using 

 methods outlined by Schefler (1979). These rela- 

 tionships were also tested using a Wilcoxon 

 Signed Ranks test (Sokal and Rohlf 1981). Owing 

 to the difference in increment types, vertebrae 

 were not considered in these comparisons. 



To test the consistency of age estimates within 

 and between readers, a subsample of 20 of each 

 hardpart was read three times each by two 

 readers. Age estimates were compared using the 

 Average Percent Error (APE) method of 

 Beamish and Fournier (1981). Mean age esti- 

 mates of each of these comparisons were com- 

 pared using the Wilcoxon Signed Ranks test. 

 Uncorrected anal and dorsal spine band counts 

 were utilized for all reader comparisons. 



RESULTS 



Hardparts and morphometric data were taken 

 from a total of 211 male and 105 female blue 

 marlin. Males ranged in size from 114.8 cm 

 UFL (19.1 kg) to 263.1 cm UFL (170.3 kg) and 

 females from 147.0 cm UFL (20.9 kg) to 445.8 

 cm UFL (748.0 kg). The 263.1 cm UFL male 

 and the 445.8 cm UFL female are the largest 

 specimens of blue marlin from which biological 

 data have been reported in the hterature. The 

 mean length of females (264.9 cm UFL) was 

 significantly greater than that of males (205.1 cm 



Table 1 . — Summary of numbers and size ranges of Pacific Makaira nigricans from wfiich 

 skeletal hardparts and measurements were collected. LJFL = lower jaw-fork lengtfi. AR 

 = anal spine radius, DR = dorsal spine radius, SW = sagittal otolitfi weight, CD = 

 centrum cone depth. 



LJFL (cm) 



Weight (kg) 



Hardpart size 



831 



