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Fishery Bulletin 105(1) 



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Figure 4 



Standardized life history transects for female Chesapeake Bay striped bass (Morone saxatilis) collected 

 in 2000. ID, an identification number assigned to each fish, is presented above each panel. Z-score 

 indicates standardized salinity records for each fish where Z = (record-mean)/standard deviation. 

 Dashed line demarcates the mean. 



two important differences. First, we did not observe 

 >90% oceanic incidence at >900 mm TL (877 mm FL) 

 (Table 1). Rather, a substantial fraction of striped bass 

 remained resident in Chesapeake Bay throughout their 

 lives regardless of age or size. At ages >12 years, 25% of 

 the female sample was estimated to have be resident in 

 Chesapeake Bay. As an extreme example, one individual 

 female resided in freshwater during its entire 11-yr 

 lifespan. Secondly, early rates of oceanic migrations at 

 sizes <700 mm TL (<685 mm FL) were substantially 

 higher than rates indicated in the Dorazio et al. (1994) 

 model, which predicted <5% of individuals migrate to 

 ocean waters. Several factors may have contributed to 

 the different results. Dorazio et al. (1994) predicted 

 the degree to which Chesapeake Bay striped bass mi- 

 grate to coastal regions north of Cape May New Jersey. 

 Thus, their recapture sample represents only a subset 

 of possible coastal fish. This bias would tend to under- 

 estimate oceanic residence; yet the Dorazio et al. (1994) 

 estimates tend to be higher for larger mature striped 

 bass. Recapture and reporting rates probably varied 

 between coastal and Chesapeake regions because of 

 more restrictive fishing regulations in Chesapeake Bay 

 that contributed to an overestimate of migrant fish to 

 northern ocean habitats. 



In comparing our results to those of past tagging 

 studies, we must also carefully consider limitations to 

 the otolith microchemistry approach. We have sought to 

 overcome some of the past hurdles regarding low sample 

 size and resolution, yet these remain principal concerns. 

 Despite large improvements in microprobe technology, 

 otolith microchemistry remains a very expensive and 

 time-consuming procedure to evaluate population-spe- 

 cific patterns in fish migration. Sample sizes, while 

 larger than in many past projects, remain modest. Also, 

 ages and sizes were not uniformly distributed in the 

 populations sampled because of strong year classes, 

 and this lack of uniform distribution would curtail 

 generalizations across size and age classes. This strong 

 year class phenomenon is common in striped bass, and 

 it is likely that migration patterns in Chesapeake Bay 

 striped bass typically will be influenced by dominant 

 year classes (Merriman, 1941). 



A central assumption in using strontium as a tracer 

 of salinity levels is that the ratio of strontium to cal- 

 cium (Sr:Ca) in the otolith can accurately distinguish 

 between oceanic (salinity >29) and estuarine (salinity 

 <30) habitat use. First, the designation, between oce- 

 anic and estuarine water is somewhat arbitary, par- 

 ticularly considering that the mouth of Chesapeake 



