Szedlmayer et al Growth of age-0 Cynosc/on regslis in Chesapeake Bay 



749 



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 sample 



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Sep 



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Figure 5 



Age of weakfish estimated from scale circuli for 

 1983, versus frequency (number/2-minute tow), by 

 station, date, and cohort in Chesapeake Bay-York 

 River, VA. Cohort 1 = open bars, cohort 2 = solid 

 bars, and cohort 3 = cross-hatched bars. 



The earliest recruits in cohort 4 were first collected at 

 the upper estuary station (5), then appeared to spread 

 down the estuary in subsequent collections (Fig. 6). An 

 up-the-estuary movement with age pattern was also 

 supported by the mean ages associated with each sta- 

 tion, because weakfish were significantly older as the 

 distance from the Bay mouth station (1) increased 

 (Table 3), and by an increase in total catch-per-unit- 

 effort up the estuary with season (Fig. 3). Different 

 cohorts appeared to segregate habitats. In 1983, cohort 

 1 was more common further up the estuary compared 

 with other cohorts, while cohort 2 dominated the mid- 

 dle habitats (Fig. 5). Cohorts 3 and 4 were lower in 

 abundance and it is difficult to suggest a pattern, while 

 cohort 5 appeared dominant at all stations after August 

 1984 (Fig. 6). 



Discussion 



To our knowledge this is the first clear identification 

 of multiple age-0 weakfish cohorts, and they showed 

 significantly different growth rates and appeared to 

 partition habitats. Earlier, Massmann (1963) suggested 

 the existence of age-0 multiple cohorts from bimodal 

 length-frequency distributions, but did not examine 

 growth rates or differential habitat use. Except for two 

 early studies (Buchanan-Wollaston and Hodgson 1929, 

 Cooper 1937) reports of multiple cohorts in the juvenile 

 stage of fishes are few (Shlossman and Chittenden 

 1981, DeVries and Chittenden 1982, Crecco and Savoy 

 1985, Kumagai et al. 1985, Eckert 1987, Isely et al. 

 1987, Wicker and Johnson 1987). This may be because 

 of the difficulty of aging juvenile fishes (Geffen 1986, 



