62 



Abstract — Oceanic incidence and 

 spawning frequency of Chesapeake 

 Bay striped bass iMorone saxatilis) 

 were estimated by using microchemi- 

 cal analysis of strontium in otoliths. 

 Otoliths from 40 males and 82 females 

 sampled from Maryland's portion of 

 the Chesapeake Bay were analyzed for 

 seasonal and age-specific patterns in 

 strontium and calcium levels. The pro- 

 portion of oceanic females increased 

 from 509c to 75% between ages seven 

 to 13; the proportion of oceanic males 

 increased from 20% to -50% between 

 ages four to 13. Contrary to an earlier 

 model of Chesapeake Bay striped bass 

 migration, results indicated that a 

 substantial number of males under- 

 took oceanic migrations. Further, 

 we observed no mass emigration of 

 females from three to four years of age 

 from the Chesapeake Bay. Seasonal 

 patterns of estuarine habitat use were 

 consistent with annual spawning runs 

 by striped bass of mature age classes, 

 but with noteworthy exceptions for 

 newly mature females. Evidence of an 

 early oceanic presence indicated that 

 Chesapeake Bay yearlings move into 

 coastal regions — a pattern observed 

 also for Hudson River striped bass. 

 Otolith microchemical analyses 

 revealed two types of behaviors (estua- 

 rine and oceanic) that confirm migra- 

 tory behaviors recently determined 

 for other populations of striped bass 

 and diadromous species (e.g., Ameri- 

 can eels [Anguilla rostrata] American 

 shad [Alosa sapidissima] and white 

 perch [Morone Americana]). 



Oceanic migration rates of Upper Chesapeake Bay 

 striped bass (Morone saxatilis), determined by 

 otolith microchemical analysis* 



David H. Secor (contact author)^ 

 Philip M. Piccoii^ 



Email for D H Secor: secori@cbl.umces.edu 



' Chesapeake Biological Laboratory 

 University of Maryland Center for Environmental Science 

 Solomons, Maryland 20688 



^ University of Maryland 

 Department of Geology 

 College Park, Maryland 20742 



Manuscript submitted '23 July 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 17 April 2006 by the Scientific Editor. 



Fish. Bull 105:62-73 (2007). 



As an estuarine-dependent species, 

 striped bass (Morone saxatilis) dem- 

 onstrate large plasticity in migration 

 patterns (Secor and Piccoli, 1996). 

 Striped bass in Chesapeake Bay are 

 partial migrants; only a fraction of 

 individuals will leave estuarine habi- 

 tats for oceanic waters (Kohlenstein, 

 1981). Never the less, Chesapeake 

 Bay striped bass are the major con- 

 tributors to interjurisdictional ocean 

 fisheries (Merriman, 1941; Wirgin et 

 al., 1993). Rates of contributions by 

 Chesapeake Bay striped bass to those 

 fisheries are determined by lifetime 

 patterns of habitat use, ontogenetic 

 rates of egress from Chesapeake 

 Bay, and regional rates of exploita- 

 tion and natural mortality (Dorazio 

 et al., 1994). Rates of oceanic resi- 

 dence have been shown to vary by 

 sex and increase with age. Analyzing 

 striped bass tagged in the Potomac 

 River, Kohlenstein (1981) advanced 

 the working hypothesis that young 

 striped bass remain in or near the 

 tributary in which they were spawned 

 for two or three years. At this point 

 a substantial proportion of immature 

 females (ca. 50%) emigrate from the 

 Bay, remaining in ocean waters until 

 sexually mature (age 5-7 years). In 

 contrast, males are mature by age 

 2 but remain in the Bay throughout 

 their lives. This hypothesis remains 

 untested, although substantial devi- 

 ation from this proposed pattern is 

 indicated by tagging studies and catch 

 records. 



From recaptured striped bass 

 tagged on Chesapeake Bay spawning 

 grounds, Dorazio et al. (1994) esti- 

 mated that by 800 mm total length 

 (TL), approximately half of the popu- 

 lation (males and females combined) 

 used ocean habitats. This length 

 would correspond to an age of sev- 

 en to 10 years (Secor et al., 1995b). 

 Tagging studies comprise quasilon- 

 gitudinal analyses, which could pro- 

 vide estimates of age-specific egress 

 rates if tagged and recaptured fish 

 are representative of the population. 

 However, striped bass are moderately 

 long lived and show migration behav- 

 iors that vary substantially with sex 

 and age. Therefore, tagging studies 

 often do not comprise sufficient spa- 

 tial and temporal scales to provide 

 the precise information needed to pre- 

 dict how Chesapeake Bay striped bass 

 contribute to coastal fisheries. 



Striped bass longevity exceeds 

 30 years (Merriman, 1941; Secor et 

 al., 1995b). Life table analysis has 

 indicated that maximum reproduc- 

 tive rate occurs relatively late in life 

 (10-12 years) (Secor, 2002) and that 

 accumulation of adult biomass (repro- 

 ductive potential) represents an im- 

 portant "storage mechanism" (Warner 

 and Chesson, 1995), improving the 



' Contribution 4041 of the University of 

 Maryland Center for Environmental Sci- 

 ence, Chesapeake Biological Laboratory, 

 Solomons, Maryland. 



