Application of otolith microchemistry 

 analysis to investigate anadromy 

 In Chesapeake Bay striped bass 

 Morone saxatilis* 



David H. Secor 



The University of Maryland System. Center for Environmental and Estuarine Studies 

 Chesapeake Biological Laboratory, Solomons, Maryland 20688-0038 



Management of Chesapeake Bay and 

 coastal striped bass Morone saxa- 

 tilis fisheries is affected by migra- 

 tion of large Chesapeake adults in- 

 to coastal waters. Tagging studies 

 during the 1930s and 1950s indi- 

 cated that a small percentage of 

 Chesapeake striped bass contribute 

 to the coastal fishery (AHadykov and 

 Wallace 1952, Mansueti 1961, Mass- 

 man and Pacheco 1961). However, 

 work on age- and sex-specific migra- 

 tion patterns (Chapoton and Sykes 

 1961, Kohlenstein 1981) suggested 

 that about half of the females aged 

 3 + migrate out of the Bay. The cur- 

 rent consensus appears to be that 

 young striped bass remain in or 

 near the tributary in which they 

 were spawned for 2 or 3 years; 

 thereafter most males remain in 

 the Bay, while a substantial number 

 of females migrate out of the Bay 

 and remain in coastal waters until 

 sexually mature (Chapman 1987, 

 Setzler-Hamilton and Hall 1991). 

 Although facultative anadromy is 

 suggested by tagging studies, age- 

 and sex-specific rates of anadromy 

 remain largely unknown (ASMFC 

 1990). 



Wave-length dispersive electron 

 microprobe analysis of strontium/ 

 calcium ratio (Sr/Ca) in otoliths has 

 recently been employed as a method 

 for distinguishing between fresh- 

 water and marine life-history phases 



• Contribution 2368, Center for Environmen- 

 tal and Estuarine Studies, The University 

 of Maryland System. 



of individual fishes (Casselman 1982, 

 Radtke et al. 1988, Kalish 1990). Sr 

 is substituted for Ca into the lattice 

 of aragonitic calcium carbonate 

 (Kinsman and Holland 1969), and in 

 otoliths the rate of substitution is in 

 proportion to its abundance in the 

 endolymph (Kalish 1989). Sr con- 

 centration in seawater is more than 

 one order of magnitude greater 

 than in freshwater (Bagenal et al. 

 1973, Radtke et al. 1988, Kalish 

 1990, Ingram and Sloan 1992). 

 Therefore, Sr levels in otoliths of 

 fish exposed to seawater should be 

 substantially higher than those ex- 

 posed to freshwater. 



Sr/Ca ratio in otoliths of anad- 

 romous striped bass was analyzed 

 to determine its usefulness in chart- 

 ing individual migratory histories. 

 In a prospectus, Coutant (1990) sug- 

 gested a similar application to in- 

 vestigate patterns of estuarine use 

 by Chesapeake Bay and Roanoke 

 River striped bass. Here, I looked 

 for a seasonal pattern in otolith 

 Sr/Ca ratios that was consistent 

 with anadromous behavior. An an- 

 nual cycle of low Sr/Ca ratios dur- 

 ing spring (exposure to Sr-poor 

 freshwater) and high ratios during 

 fall and winter (exposure to Sr-rich 

 saltwater) was expected in large 

 adults. If such a pattern existed, 

 then further research and applica- 

 tion would be justified. Analysis of 

 Sr/Ca composition could be applied 

 to problems of migratory behavior, 

 spawning, hatchery contribution 

 to coastal stocks, definition of life- 



history traits, environmental degra- 

 dation (Coutant 1990), and conse- 

 quences of anadromy to recruit- 

 ment (e.g., KaHsh 1990). 



In this investigation, I related 

 Sr/Ca ratios to annuli which are 

 assumed to form in spring (see Dis- 

 cussion). I used a less traditional 

 definition for annulus, " . . .a ridge 

 or a groove in or on the [hard] struc- 

 ture. . ." (Wilson et al. 1987), be- 

 cause opaque and translucent zones 

 did not adequately describe the 

 microstructure observed under 

 scanning electron microscopy or 

 light microscopy. 



Methods 



Sr/Ca ratios were examined for five 

 large adults from the Chesapeake 

 Bay and South Carolina (Table 1). 

 Adults from the Chesapeake were 

 presumed to be anadromous based 

 on their size (Setzler-Hamilton and 

 Hall 1991); the South Carolina 

 population is a freshwater popula- 

 tion, resident to the Santee-Cooper 

 watershed (Secor et al. 1992). 

 Chesapeake Bay fish (n 3) were col- 

 lected by charterboat fisherman 

 from Solomons, Maryland during 

 the May 1991 "Maryland Trophy 

 Season", presumably caught in up- 

 per Bay waters. South Carolina fish 

 were collected at a 1989 fishing 

 tournament. Otoliths were removed, 

 cleaned in 10% sodium hypochlorite 

 solution (bleach), and rinsed with 

 deionized water. They were em- 

 bedded in Spurr epoxy, sectioned in 

 a transverse plane with a Buehler 

 Isomet saw, and mounted on a glass 

 slide. Otoliths were polished (see 

 Secor et al. 1991) until all annuli 

 were visible with transmitted light 

 on a compound microscope. Otolith 

 sections were further polished with 

 3 Jim alumina to limit any surface 

 structure that could cause artifacts 



Manuscript accepted 13 July 1992. 

 Fishery Bulletin, U.S. 90:798-806 (1992). 



798 



