158 



Fishery Bulletin 98(1) 



different. Age estimates from otolith sec- 

 tions were less precise than from fin-spine 

 sections ( Fig. 2B). Absolute imprecision was 

 3.3 years and the CV on paired differences 

 was 14.8%. No significant bias occurred in 

 otolith interpretations between readers. In 

 a comparison of ages estimated by a single 

 reader from otolith sections and from cor- 

 responding fin-spine sections (i.e. from the 

 same fish), the former were significantly 

 lower than the latter (Fig. 2C; mean dif- 

 ference=5 yr, ^=9.01, P<0.05). The bias was 

 most apparent for presumed by older fish. 



Validation of the fin-spine aging method 



Marginal increment ratios for fish collected 

 in late winter and spring (February-April) 

 were significantly lower than those for 

 summer and fall (Fig. 3; Kruskal-Wallis 

 test;P=0.04). Mean MIR was 18% in spring, 

 33% in summer, and 36%. in fall. The high- 

 est rate of marginal increment completion 

 was observed for winter months (Decem- 

 ber-February), although sample size was 

 very small for these months (n=3). 



Readings of annuli from hatchery-reared 

 sturgeon resulted in exact age estimates. 

 The sturgeon were 4-i- years old and annuli 

 were clearly defined. There was a distinct 

 difference in the shape of fin spines from 

 hatchery-reared and wild juvenile stur- 

 geon (Fig. IC). Hatchery-reared fish exhib- 

 ited irregularly shaped, compressed annuli 

 which could indicate erosion or injury, 

 but were nonetheless easily recognized. In 

 OTC-injected fish, a distinct OTC mark fol- 

 lowed by an opaque zone was apparent in 

 all fin spines examined three months after 

 injection. The fish did not show any symp- 

 toms of stress following fin-spine removal. The only 

 sample examined at fifteen months after injection 

 exhibited a clear OTC mark that was followed by 

 opaque and translucent zones. 



Microchemical analysis 



The concentrations of calcium and phosphorus in 

 peripheral regions of fin spines showed significant 

 seasonality (Kruskal-Wallis test, P<0.04; Fig. 4). Fin 

 spines collected in November were significantly lower 

 in calcium and phosphorus than those collected in 

 March, June, and September. Calcium-to-phosphorus 

 ratios increased significantly from March through 

 November (Kruskal-Wallis test, P=0.04). Plots of cal- 



100 



80 



60 



40 



20 



o 



e 



Feb. 



April 



June Aug. 



Month 



Oct. 



Dec. 



Spring 

 (Mar-May) 



Summer 

 (June-Aug.) 



Season 



Fail 



(Sept. -Nov.) 



Figure 3 



(A) Marginal increment ratios (MIR) ± one standard error for sectioned 

 Hudson River Atlantic sturgeon pectoral fin spines evaluate current 

 season's growth. Numbers represent sample size. (B) Marginal incre- 

 ment ± ^b'7( confidence interval for data grouped by season. MIR = 

 Ml X 1/A, where Ml = the width of the outermost opaque zone (mar- 

 ginal increment) and A = the mean width of the three annuli deposited 

 previous to the marginal increment. 



cium and phosphorus in fin spines revealed cyclical 

 trends in both elements, with peaks associated with 

 translucent zones (Fig. 5). 



Growth 



The size-age relationship for prespawning fish, as 

 judged by interpretations of annuli in fin spines, was 

 best fitted by a power regression (r-= 0.75; Fig. 6). 

 Von Bertalanffy models for both males and females 

 considerably underestimated length at age for sub- 

 adults. Over all life history portions, the fit of the von 

 Bertalanffy model was better for females (ages 2-42; 

 r^=0.56) than for males (ages 4-36; r-=0.33) owing to 

 the broader range of ages and lengths in our sample 



