LAROCHE and DAVIS: NORTHERN PUFFER 



Table 1. — Calculated total length at end of each year of life of male and female 



northern puffer. 



vertebral length as body length increments 

 decrease. 



The second criterion was met by the agree- 

 ment of measured lengths with length at each 

 age as calculated by the Lee method (Lagler. 

 1956) (Table 1). Mean weighted lengths at each 

 age coincided closely with the measured length 

 for fish 1 yr younger because most fish were 

 taken in the fall after the growing season and 

 in late spring before the growing season. Total 

 vertebral length and distance between annuli 

 across the center of the vertebra were used to 

 calculate lengths. Measurements were made 

 along the shortest straight line connecting the 

 approximate midpoints of annuli and the cen- 

 trum edge (Figure 4). The distance between 

 annuli could not be measured with certainty 

 in 5% of the fish because the annular step was 

 expanded into a broad, opaque shelf without a 

 distinct end point (Figure Id). The plot of 

 body length on vertebral length was approxi- 

 mately linear, and the regression equation 

 was L = 27.52 + 3.28 F with a significant cor- 

 relation coefficient of 0.9827 where L is total 

 length in millimeters and V is vertebral length 

 in ocular micrometer units. 



The third and fourth criteria were met by 

 the correspondence of peaks in the length- 

 frequency plots for each age group with peaks 

 in the plot of the entire sample and by the 

 regular increase in number of annuli with in- 

 creasing body length (Figure 5). Overlap in 

 mean body length among age groups was 

 caused by early summer annulus formation in 



yearlings coupled with an extended period of 

 annulus formation in older age groups. The 

 wide range of lengths attained in the first grow- 

 ing season also contributes to the observed 

 overlap of body lengths. The biomodal distribu- 

 tion of females in age group I was caused by 

 the great number of fish larger than 210 mm 

 taken in April and May from culled and sorted 

 commercial pound net catches. Throughout the 

 rest of the sampling period, the majority of 

 fish came from unculled pound net and haul 

 seine catches. 



Therefore, the annulus on northern puffer 

 vertebrae has been validated based on agree- 

 ment with these criteria. 



DORSAL 



POSTERIOR 



B 



ANTERIOR 



VENTRAL 



Figure 4. — Measurements taken on vertebral sections 

 which were used in calculating length at age: (A) vertebral 

 length, (B) distance between annuli across center of 

 vertebra. 



959 



