70 



Fishery Bulletin 105(1) 



ra 



26 

 24 

 22 

 20 

 18 

 16 



26 

 24 

 22 

 20 

 18 

 16 



Male < 7 years 



0.25 0.5 0.75 



Female < 7 years 



30 



26 



22 



0.25 0.5 0.75 



33 



29 



25 



21 



Male > 6 years 



0.25 0.5 0.75 



Female > 6 years 



0.25 0.5 0.75 



Interval 



Figure 5 



Seasonal patterns in salinity exposure as recorded in the otoliths of Chesapeake 

 Bay striped bass iMorone saxatilis) collected in 2000. Mean salinities and standard 

 errors are shown for age classes <7 and >6 years. Seasonal interval indicates 

 the relative distances from the opaque zones in the otolith, which are formed in 

 early spring. Intervals represent the seasons as a proportion of annual otolith 

 increment width. 



ging studies (Kohlenstein, 1981; Dorazio et al., 1994). 

 Further, increasing trends in oceanic habitat use with 

 age observed in our study are consistent with the two 

 previous tagging studies. The increased incidence of 

 males in ocean environments shown in our study and 

 previous ones could reflect a true increased likelihood 

 of emigration, perhaps driven by increased striped bass 

 density, or by poorer habitat conditions in Chesapeake 

 Bay. This view would be consistent with the near his- 

 torically high abundances of Chesapeake Bay striped 

 bass and the increased incidence of summertime hy- 

 poxia in Chesapeake Bay during the past two decades 

 (Hagy et al., 2004). However, error due to the otolith 

 microchemistry approach in classifying fish to oceanic 

 or estuarine habitat use must be acknowledged and 

 caution should precede application of the estimates of 

 oceanic residence provided in this study. 



Spawning frequency 



In general, otolith microchemical analyses gave evidence 

 for the view that most mature striped bass undertake 

 annual spawning runs. For females, immature age 

 classes did not show significant seasonality in changes 

 in salinity, but many mature age classes did. Further, 

 cycles in salinity were largely defined by a nadir that 



occurs during early spring as evidenced by changes in 

 the chemistry of the opaque zone of the otolith. Thus, 

 evidence of the use of low-salinity habitat was recorded 

 near the opaque zone, consistent with the view of an 

 annual up-estuary migration to low-salinity spawning 

 habitats. Where such nadirs were not observed in the 

 otolith microchemistry, two interpretations are plausible: 

 1) no spawning migration occurred, or 2) the otolith 

 microchemistry method had insufficient resolution to 

 allow us to detect the spawning migration. The resolu- 

 tion issue relates to two problems. First, the spacing 

 of the microprobe assays could have been such that a 

 spawning run event was missed. Second, spawning- 

 run striped bass occur in low-salinity regions for short 

 periods during which they are not growing and thus 

 incorporating Sr material into their otoliths. In this 

 instance, there would be an insufficient signal for oto- 

 lith microanalysis of Sr to detect. Despite these likely 

 sources of error, we were still able to detect a dominant 

 annular cycle in otolith Sr for mature age classes of 

 males and females. Therefore, we believe that the otolith 

 microchemistry analysis supports annual spawning for 

 the majority of mature Chesapeake Bay striped bass. 



Alternatively, spawning in striped bass may occur 

 less than once a year. Less than an annual spawning, 

 once thought to be specific to relatively few taxa (e.g.. 



