Stevenson and Secor: Growth of Acipenser oxyr/nchus 



159 



of females (Fig. 7A). Males grew faster but 

 reached a smaller asymptotic length at a 

 younger age than did females. Females grew 

 more slowly (K=0.07) toward a significantly 

 larger maximum length (251 ±12.8 cm). The 

 asymptotic growth phase for females and 

 males was 12-42 and 11-28 years, respec- 

 tively. Estimates of growth coefficients, K, 

 were significantly different between sexes 

 (/=73.2, df=431, P<0.05). Log transformation 

 of the data did not correct for the error struc- 

 ture. Residuals from the models were desig- 

 nated as corresponding either to fish of the 

 size at entry into the fisheries ( 152 cm TL in 

 New York and after 1993 in New Jersey), or 

 to larger or smaller fish. The resulting resid- 

 ual plots indicated that the faster-growing 

 males were harvested just as they reached 

 size at entry ( positive residuals) and that the 

 slower-growing females entered the fishery 

 at much older ages (negative residuals; Fig. 

 7B). The modeled growth pattern for females 

 appeared more biased than that for males 

 owing to a sharp shift in residuals from posi- 

 tive to negative at about 15 years. At older 

 ages, the von Bertalanffy model underesti- 

 mated the size of females. These patterns in 

 residuals were also apparent in males, albeit 

 less pronounced. 



Discussion 



Fin spines or otoliths? 



Owing to ease of collection and processing, 

 as well as precision and accuracy in aging, we rec- 

 ommend the use of fin spines rather than otoliths 

 for demographic analysis of Atlantic sturgeon. Prep- 

 aration techniques used in this study (embedding, 

 sectioning, and polishing) may have improved the 

 visual resolution of annuli in pectoral-fin spines over 

 that reported in earlier investigations. 



Annuli in sturgeon otoliths and, as a result, growth 

 rates, have been grossly misinterpreted in the past 

 owing to examination of the external surface of hard 

 parts only (Greeley, 1937). Especially in presumed 

 older individuals, otoliths should not be used to 

 verify age estimates based on fin spines. Annular 

 clarity diminishes towards the distal end of the oto- 

 lith (more recent growth), which may result in lower 

 age estimates. In addition, individuals must be sacri- 

 ficed to collect otoliths. Concern over declining stur- 

 geon populations should restrict the size of otolith 

 samples. 



Precision and accuracy 



Age estimates based on fin spines were unbiased 

 and precise. Aging imprecision for Atlantic sturgeon 

 was similar or better than imprecision reported for 

 other long-lived (>20 yv) species, for which precision 

 is often affected by narrow annuli, which result from 

 reduced growth rates in older fish (Rien and Beames- 

 derfer, 1994; Table 1 ). The annual patterns of mar- 

 ginal increment ratio (MIR), observations on fish of 

 known age, and microchemistry have supported the 

 hypothesis that a pair of opaque and translucent 

 zones forms annually in Atlantic sturgeon fin spines. A 

 small sample of OTC-marked juveniles also indicated 

 annual annulus growth (Stevenson, 1997). Results for 

 Atlantic sturgeon were similar to Huff's (1975) anal- 

 ysis of Gulf sturgeon (Acipenser oxyrinchus desotoi) 

 fin-spine sections, in which a higher percentage of 

 fin-spine sections showed that a completely formed 



