Limburg et al.: Growth, mortality, and recruitment of larval Morone spp. 



87 



Retrospective early life histories of juvenile versus 

 larval striped bass 



Larval and juvenile striped bass from the 1994 year 

 class had similar patterns of early growth, as mea- 

 sured by mean growth (mm/d I through age 7 days 

 after hatching. In both groups, growth rates in- 

 creased monotonically from May through early July 

 corresponding with before, during, and after the zoo- 

 plankton bloom (P<0.01; Table 4). Juvenile mean 

 growth rates before and during the zooplankton 

 bloom were higher (though not significantly so) than 

 larval growth rates in the corresponding periods. 

 However, mean 7-d growth rates of postbloom juve- 

 niles were significantly {F( 1,87)=21.03, P<10-*) lower 

 than growth rates of postbloom larvae. 



The frequency (distribution of hatching dates) of 

 juvenile striped bass born in the 6-d cohorts begin- 

 ning 1 May did not correlate well with the index of 

 recruitment (G/Z) developed from the larval data 

 {Frequency=0.n8+0.021 iG/Z), r^=0.03). 



Because of our ability to "hind-cast" the distribu- 

 tion of hatching dates of juveniles and larvae, we 

 estimated the relative proportions of both larvae and 

 juvenile striped bass that would have begun to feed 

 during the zooplankton bloom (assuming that feed- 

 ing begins at day 5 after hatching). For this analy- 

 sis, we analyzed the fish response to Bosmina and 

 copepods. For Bosmina we assumed that fish with 

 hatching dates between 29 May and 8 June would 

 be able to feed on Bosmina: we further assumed that 

 fish hatched between 5 June and 17 June would also 

 be able to take advantage of the bloom of copepods 

 (note that in this analysis we assume that Bosmina- 

 feeders occurred above Haverstraw Bay and that 

 copepod feeders occurred throughout the river). 



Larval distributions indicated that 3T7( of the popu- 

 lation began to feed after the bloom of Bosmina (Fig. 

 4A), and 26% initiated feeding during the bloom. Of 

 larvae that occurred in the geographic range of Bosmina 

 (at New Hamburg and Kingston), over half began to 

 feed after the bloom and less than 20% began feeding 

 during the bloom. In contrast, 44% of juvenile striped 



Pre 



During 



I Larvae □Juveniles 



Post 



Pre 



During 



[Larvae □Juveniles 



Post 



Figure 4 



Fraction of larval (black bars) and juvenile 

 (gray bars) 1994 striped bass populations that 

 were estimated to be feeding before, during, 

 and after blooms of (A) Bosmina freyi and (B) 

 copepods in the Hudson River. 



bass began to feed during the bloom of Bosmina (Fig. 

 4A); and of the fish identified as first feeding prior to 

 the onset of the bloom, 23% were hatched after 25 May, 

 so that these fish would have been relatively close to 

 first feeding at the time that Bosmina numbers in- 

 creased exponentially. Those survivors to the juvenile 

 stage that began to feed after the Bosmina bloom com- 

 posed the smallest fraction ( 26% ). The first-feeding dis- 

 tributions of larvae and juveniles differed significantly 

 with respect to the Bosmina bloom (2x3 contingency 

 analysis, x^=13.4, df=2, P<0.01 ), whereas distributions 

 of larvae and juvenile fish with respect to the bloom of 

 copepods did not differ from one another (x'=3.7; Fig. 

 4B). Thus the time period associated with the Bosmina 

 bloom, and not the copepod bloom, appears to have been 

 related to successful striped bass recruitment. 



Discussion 



Evidence from this study provides some support for 

 the relation between larval growth rates and tern- 



