80 



Abstract.— We measured age and 

 growth of larval striped bass {Morone 

 saxatilis) and white perch (M. ameri- 

 cana) and tested whether growth and 

 survival were enhanced in relation to 

 a seasonal pulse ("bloom") of high zoo- 

 plankton abundance. Growth rates 

 were lowest before the zooplankton 

 bloom and highest afterwards for both 

 fish species. An index of recruitment po- 

 tential (instantaneous growth rate. G. 

 divided by instantaneous mortality 

 rate, Z) did not relate clearly to either 

 water temperature or to zooplankton 

 abundance in the case of striped bass 

 but did relate to both factors for white 

 perch. Retrospective analysis of hatch 

 dates in recruited juvenile striped bass 

 from the same year class indicated that 

 later, faster growing cohorts were un- 

 der-represented when compared to the 

 larval cohort distribution, and that co- 

 horts that co-occurred with high densi- 

 ties of the cladoceran zooplankton 

 Bosmina freyi were over-represented. 

 Comparison of these results with simi- 

 lar analyses from other systems sug- 

 gests that biotic controls on year-class 

 strength may predominate in estuarine 

 systems where physical factors are rela- 

 tively damped (Hudson) but may play 

 relatively minor roles in those systems 

 with high physical variability. 



Growth, mortality, and recruitment of larval 

 Morone spp. in relation to food availability 

 and temperature in the Hudson River 



Karin E. Limburg 



Michael L. Pace 



Institute of Ecosystem Studies, Millbrook, New York 12545 

 Present address (for K Limburg) Department of Systems Ecology 



University of Stockholm 



S-106 91 Stockholm, Sweden 

 E-mail address (for K Limburg) Karin_L(g'system ecology su se 



Kristin K. Arend 



Oberlin College 

 Oberlin, Ohio 44074 



Manuscript accepted 1 April 1998. 

 Fish. Bull. 97:80-91(1999). 



Survival (during the first year of life 

 determines the year-class strength 

 of many fish. The degree to which 

 biotic or physical factors regulate 

 recruitment of fish from larval to 

 juvenile stages varies from one 

 aquatic system to another, and even 

 temporally within systems (Leggett 

 and DeBlois, 1994). The factors pro- 

 moting or inhibiting recruitment 

 are a subject of intense interest both 

 in theoretical analysis and practical 

 management offish populations (cf 

 Hilbom and Walters, 1992), Mortal- 

 ity of young fish below harvestable 

 size is difficult to observe and diffi- 

 cult to measure by means of standard 

 approaches to population assessment 

 (e.g. mark and recapture). 



The age and growth rates of 

 young fish, however, can be pre- 

 cisely quantified with otolith analy- 

 sis (cf. Campana and Neilson, 1985; 

 Secor et al., 1995). This technique 

 has permitted the determination of 

 hatching dates, age, and growth 

 rates of both larvae and juveniles 

 of many species. Comparisons of 

 hatching dates and gi'owth between 

 life stages (e.g. larvae vs. juveniles) 

 allow inferences about the fates of 

 larvae. For example, if larval sur- 

 vival is particularly high during a 

 specific time period, analysis of ju- 



venile hatch dates should reflect the 

 differential survival (assuming ad- 

 equate sampling). These measures 

 can also be used with repeated sam- 

 plings of the population to track the 

 growth and mortality of specific age 

 classes (e.g. weekly cohorts) over 

 time. Relationships between these 

 cohort-based rates can be analyzed 

 with respect to variables such as 

 food availability, predation, and the 

 physicochemical environment. 



We previously documented that 

 larval striped bass (Morone saxa- 

 tilis) and white perch (M. ameri- 

 cana), which co-occurred with in- 

 creases in crustacean zooplankton 

 in the tidal Hudson River, showed 

 a potential energetic advantage 

 compared with larvae that preceded 

 the zooplankton increase (Limburg 

 et al., 1997). A major increase 

 ("bloom") in zooplankton in early 

 summer is a key feature of the 

 Hudson estuary. Larvae occurring 

 before the bloom are exposed to 

 sparse zooplankton densities and 

 low temperature, both of which are 

 associated with mortality risks 

 I Rogers and Westin, 1981; Chesney, 

 1989; Margulies, 1989; Uphofif, 

 1989; Tsai, 1991; Cowan et al., 

 1993 ). Larvae occurring during and 

 after the bloom have high consump- 



