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Fishery Bulletin 105(1) 



habitat use) were determined from at least five point 

 measurements taken across the last completely-formed 

 annulus (i.e., the last full year of life prior to winter). 

 Opaque zone formation on the otolith occurs just prior 

 to the spawning season (Zlokovitz et al., 2003); therefore 

 measurements were taken between the penultimate 

 and most peripheral (recently formed) opaque zones. 

 We selected the record of maximum salinity, because 

 at least one point in this series can be influenced by 

 the previous year's spawning run. Oceanic habitat use 

 was defined as salinities >29, and individual fish were 

 classified accordingly. Because of unequal sampling 

 among ages, we analyzed four age classes by sex: 4-6, 

 7-9, 10-12, and 13-18 years of age. Two-way classifi- 

 cation tables were constructed to evaluate differences 

 between age classes and sexes in probability of recent 

 oceanic residence. 



Life history transects and spawning frequency 



Life history transects of salinity exposure, a series 

 of Sr:Ca ratios from the juvenile period to the end of 

 life, were constructed from EPMA measurements from 

 30 female and 10 male striped bass. This subsample 

 was drawn from the upper Bay (n=2), mid-Bay {n=27), 

 and Choptank River («=11). To weight seasonal data 

 among ages, time series were selected so that four or five 

 analyzed points were included for each annulus. Data 

 were standardized (Z score= {transect datum - tran- 

 sect mean)ltransect standard deviation) and plotted to 

 examine variations about the transect mean (Sokol and 

 Rohlf, 1981). 



Time-series data represented by the life history tran- 

 sects were expected to show autocorrelation across sea- 

 sonal points and ages. An appropriate method of data 

 analysis that shows interdependence among repeated 

 measures on the same individual is repeated measures 

 multivariate analysis (RM-MANOVA) (Chambers and 

 Miller, 1995). This analysis simultaneously fits several 

 dependent variables to independent factors of interest 

 (SAS, Statistical Analysis System, SAS Institute, Inc., 

 Gary, NC) and evaluates the matrix equation, 



S, = Sex/3 + E, 



where S, = salinities at seasonal points; and 



t = relative distance between successive opaque 

 zones. 



For each fish, S^ is arrayed in Ji rows, Sex contains 

 two treatment levels for each factor (male vs. female) 

 arrayed in n rows, and E is the matrix of model residu- 

 als. Degrees of freedom in the analysis depend upon 

 n, which represents the number of individual fish. To 

 avoid the problem of interdependence of seasonal data 

 for combined ages, separate MANOVAs were performed 

 for each age class. 



To conduct the RM-MANOVA, it was necessary to 

 have equal numbers of seasonal points (S,) for each age 

 class. Therefore, narrow annuli that had fewer than 



three seasonal (interannual) points were omitted from 

 analyses. This excluded analyses of some of the old- 

 est age classes, which typically exhibit narrow annuli 

 (Secor, 1992). For years sampled with more than four 

 or five seasonal points, the extra points were omitted 

 from our analysis. Selection of points to be included was 

 based upon their proximity to the axial distances of the 

 prescribed intervals (either [0, 0.25, 0.5, 0.75] or [0, 0.2, 

 0.4, 0.6, 0.8]). Individual probe points within transects 

 were separated by 10 to 35 microns. 



Results 



Demographics 



Ages among the sampled Maryland Chesapeake Bay 

 striped bass ranged from three to 18 years and sizes 

 ranged 320 to 1110 mm FL. Females were significantly 

 older and larger than males (ANOVA; P<0.01) and grew 

 at a faster rate. Males were more heavily represented by 

 ages <10 years than females in age-frequency distribu- 

 tions, although fish with ages >15 years were observed 

 for both sexes. Relatively strong year class contributions 

 within the sample occurred for 1982, 1989, 1993, and 

 1996 and coincided with high young-of-the-year juvenile 

 abundances observed in those years (Secor, 2000a). 



Oceanic incidence of striped bass 



Female fish, more often than male fish, were classified 

 as having a recent period of oceanic residence based 

 upon the analysis of the last fully formed annulus, 

 but this difference was not significant (/-, P>0.1). For 

 individual age classes with sample sizes >5, oceanic 

 incidence ranged from 60% to 75% for females and 

 from 17% to 50% for males (Table 1). There was an 

 indication that the proportion offish of both sexes with 

 oceanic residence increased with age. Oceanic inci- 

 dence was observed consistently for >50% of the females. 

 For males, oceanic incidence was 8-32% less than for 

 females within each age class. Error bars, based upon a 

 binomial probability distribution, indicated a fairly well- 

 estimated oceanic classification rate for the age class 

 10-12 years due to a relatively high sample size. For this 

 age class, oceanic incidence was estimated at 59% and 

 50% for females and males, respectively. Conversely, use 

 of oceanic habitat for males at ages <10 was poorly esti- 

 mated because of low sampling size. Indeed, estimated 

 ratios for this group could not be statistically resolved 

 from zero. With increased size, oceanic incidence (sexes 

 combined) tended to increase (Table 1), although there 

 was a decline in the proportion of fish with evidence of 

 oceanic residence from 65.8% for the size class 900- 

 999 mm FL to 46.1% for the size class >1000 mm FL. 



Life history transects 



Life history transects showed considerable variability 

 (Fig. 1). It is noteworthy that some males exhibited 



