188 



Fishery Bulletin 93(1), 1995 



Discussion 



Annulus formation in otoliths and scales 



We verified age estimates of striped bass from an- 

 nuli observed in sectioned otoliths offish 3 to 7 years 

 old. Annuli precisely and accurately reflected ages 

 in both resident and migratory Chesapeake Bay 

 striped bass. Annulus appearance at 6 and 7 years 

 was similar to that of annuli from otoliths of much 

 older individuals (Fig. 1 in Secor, 1992). Therefore, 

 we believe that annuli also are formed at a yearly 

 rate in older individuals (e.g. >20 years). Tagged 

 hatchery striped bass represent over 5% of the striped 

 bass population which over-winters in coastal wa- 

 ters off North Carolina (Laney and Cole, 1993). Thus, 



30 



20 



10 



Scole Age = Otolith Age 



10 



20 

 Otolith age (yr) 



30 



40 



i 2 



-4 



B 



10 



20 

 Otolith age (yr) 



40 



Figure 2 



(A) Scale-estimated age vs. otolith-estimated age for Maryland 

 Trophy striped bass (>91 cm TL). Scale age = 4.55 + 0.46 otolith 

 age; rc=45; ^=0.85. For reference, a line corresponding to scale 

 age = otolith age has been plotted. (B) Discrepancy between 

 otolith-estimated and scale-estimated age vs. otolith-estimated 

 age for Maryland Trophy striped bass (>91 cm TL). (Otolith age- 

 Scale age) = -4.55 + 0.54 otolith age; re=45; r*= 0.88. 



these fish will continue to provide a pool of known- 

 age material to verify age estimates in older fish. In 

 the next decade it will be possible to verify annulus 

 formation in the oldest fish of the population. 



The timing of annulus formation in otoliths was 

 not quantitatively evaluated; samples among months 

 of the year were insufficient to conduct a marginal in- 

 crement analysis (see Beckmanetal., 1988, 1990, 1991). 

 However, we did consistently observe that samples col- 

 lected during the Maryland Trophy Striped Bass Sea- 

 son in May 1991 and 1992 (see Secor, 1992) contained 

 a newly formed annulus and that no such annulus was 

 observed in otoliths of resident or migratory fish col- 

 lected in February 1993. Therefore, annulus formation 

 probably occurs during the February-April period. This 

 observation agrees with observations on season of an- 

 nulus formation in striped bass scales (Merriman, 

 1941; Heidinger and Clodfelter, 1987). 



On the basis of evidence that annuli in otolith 

 ages represent true age in older fish, we believe 

 that scales significantly underestimate age in fish 

 older than 20 years. Scale ages were not signifi- 

 cantly different from otolith ages for fish aged 5 

 to 11 years, ages that corresponded to fish 91 to 

 110 cm TL. Scale ages were, on average, 9 years 

 less than otolith ages in fish older than 20 years 

 that corresponded to fish >120 cm TL. Because 

 samples were unavailable for ages 12 to 19 years 

 owing to the scarcity of individuals from these year 

 classes (Secor et al. 4 ), we could not determine the 

 accuracy of scale ages for this period. In a similar 

 study on southeastern U.S. riverine and reser- 

 voir striped bass, Welch et al. ( 1993) observed that 

 scale ages were in good agreement with otolith 

 ages for fish <90 cm TL but that scale ages were 

 significantly lower than otolith ages for fish 90- 

 10 cm TL. For Sacramento-San Joaquin striped 

 bass, Scofield ( 1928a) found good agreement be- 

 tween age estimates made from either hardpart 

 for the first eight years offish life. 



Ageing in striped bass stock 

 assessments 



Errors in ageing can result in large biases in 

 stock assessments and in mismanagement of 

 fishery resources (Beamish and McFarlane, 

 1983; Richards et al., 1992). Scientists at the 

 turn of the century recognized that otoliths of- 

 ten provide more accurate and precise estimates 

 of age than do other hard parts (Heinke, 1904; 

 Cunningham, 1905; Haempel, 1910). Indeed, 

 early verification of age estimation based on 

 scales of striped bass relied upon comparisons 

 of age estimates with those based on otoliths 



