Secor and PIccoli: Oceanic migration rates of Morone saxatilis, determined by otolith microchemlcal analysis 



69 



Bay averages about 25-30 psu during summer and fall 

 months. Still, it was necessary to have a designation for 

 assessing habitat use, and the above designations may 

 have resulted in a liberal estimate of oceanic residence. 

 A second issue is the resolution of the relationship of 

 otolith Sr-Ca ratio to salinity. Resolution level esti- 

 mated by experimental work of Secor et al. (1995a) was 

 a salinity of 6 psu, which would support the contention 

 that estimates presented here are fairly precise if er- 

 ror is unbiased. Still, the relationship between otolith 

 Sr:Ca and salinity was logistic and very rapid changes 

 in Sr:Ca were predicted to occur with small changes 

 in salinity at salinities between 25 and 35 psu. These 

 rapid changes at high salinities could indicate higher 

 unexplained variability at salinities >24 psu. 



Finally, our samples were unequally weighted across 

 subpopulations of striped bass. For instance, no lower 

 Chesapeake Bay subpopulations (those spawning in 



the James, York, and Rappahannock systems) were 

 represented in our sample). Recent tagging studies 

 have either focused more narrowly on the Potomac 

 River (Kohlenstein, 1981) or have drawn a larger and 

 more representative sample from the Maryland sec- 

 tion of Chesapeake Bay (Dorazio et al., 1994). Studies 

 on Virginia subpopulations of striped bass have his- 

 torically shown low rates of oceanic residence (<5%; 

 Vladykov and Wallace, 1952; Massman and Pacheco, 

 1961). Kohlenstein (1981) effectively argued that these 

 and other early tagging studies (i.e., Mansueti, 1961) 

 were not appropriately stratified to provide evidence of 

 an increased likelihood of oceanic residence by larger 

 size fish. 



In sum, we believe that our otolith microchemistry 

 results indicate higher rates of early oceanic residency 

 in females and overall higher rates of oceanic migra- 

 tions by males than were observed in previous tag- 



