NOTE Secor: Otolith microchemistry analysis of Morone saxatilis anadromy 



803 



>< 



E 3 



O 



E2h 



CO 1 



Sample: PAX Juvenile-1 



4 6 



Estimated SL (mm) 



Figure 5 



Transect of Sr/Ca ratios for the early-larval period from a 

 juvenile striped bassMorcm« saxatilis sampled from the Patnx- 

 ent River, 1991. Transect distance was converted to standard 

 length using regression of standard length on otolith length 

 for Potomac River striped bass larvae (Houde et al. 1992). 

 Transect points were converted to larval lengths assuming 

 a linear growth rate and constant otolith length:fish length 

 relationship. 



-0.0062) and 1 freshwater species (Sr/Ca 0.0005- 

 0.0010). 



Radtke (1984) and others (Townsend et al. 1989, 

 Radtke et al. 1990) have shown an inverse relationship 

 between temperature and otolith Sr/Ca ratio. If there 

 were such an inverse relationship in adult striped bass 

 otoliths, then ratios would increase during fall and 

 winter and decrease during spring and summer, a pat- 

 tern which would to some degree parallel the pattern 

 seen for anadromous striped bass. 



Kahsh (1989, 1991) in recent directed research found 

 no temperature relationship for otolith Sr/Ca ratio, and 

 suggested that seasonal changes in fish physiology can 

 cause incidental correlation between temperature and 

 Sr/Ca ratios. Based on evidence for seasonal, growth. 



and age effects on Sr/Ca ratios, he pos- 

 tulated that during certain periods of active 

 metabolism, Ca-binding proteins are more 

 abundant in the serum which results in a 

 higher relative fraction of free Sr available 

 for deposition onto the otolith. If Sr/Ca 

 ratios in the otolith are controlled by phys- 

 iological processes alone, then a different 

 pattern of Sr/Ca ratios would be expected 

 compared with those observed for striped 

 bass, i.e., Sr/Ca ratios would tend to rise in 

 late-winter and early-spring during vitello- 

 genesis but might also be high during peri- 

 ods of active growth. However, physiolog- 

 ical effects such as sexual maturation and stress could 

 explain both the increase in Sr/Ca ratio after the 5th 

 annulus in Samples MD-1 and MD-3, and seasonal 

 (subannular) patterns which varied among samples 

 (e.g., the major peak which proceeded the 6th annulus 

 in Sample MD-2; Fig. 2). 



Although results exist for few species, the magnitude 

 of the salinity effect found in this and other studies 

 (Casselman 1982, KaJish 1989 and 1990) may be greater 

 than differences expected due to physiological condi- 

 tion (Kalish 1989, 1991) and temperature alone (Radtke 

 1984, Townsend et al. 1989, Radtke et al. 1990). Similar 

 to my findings, Kalish (1989, 1991) reported a three- 

 to four-fold difference in Sr/Ca ratio between groups 

 of young rainbow trout exposed to either freshwater 

 or saltwater. Casselman (1982) reported a three-fold 

 difference in Sr/Ca ratio between the marine and fresh- 

 water life-history phases of American eel. In labora- 

 tory-rearing studies on larval herring Clupea harengus, 

 temperature effects resulted in no more than a two- 

 fold difference in Sr/Ca ratios (Townsend et al. 1989, 

 Radtke et al. 1990), although a complementary field 

 study conducted by Townsend et al. (1989) showed that 

 temperatures of 1-12°C had a four-fold effect on Sr/Ca 

 ratio. Physiological condition has been associated with 

 an approximate two-fold effect on Sr/Ca ratio in juve- 

 nile Australian salmon Arripis trutta (Kalish 1989). 

 A three-fold difference in Sr/Ca ratio in otoliths is 

 consistent with the probable influence of ambient con- 

 centrations of Sr and Ca, since the Sr/Ca ratio is at 

 least four times greater in saltwater than in freshwater 

 (Casselman 1982, Radtke et al. 1988, Kalish 1989 and 

 1990). Further, Berg (1968) has shown substantially 

 less physiological discrimination against Sr than Ca in 

 scale formation, and Kalish (1989) shows excellent cor- 

 respondence between otolith microchemistry and the 

 chemical composition of endolymph that bathes the 

 otolith. Therefore, ambient levels of Sr could be 

 reflected in the otolith's microchemistry (Mugiya and 

 Takahashi 1985, Kalish 1989) dependent upon the 

 degree of physiological discrimination against Sr. 



