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Fishery Bulletin 97(3), 1999 



N 



39° 30' 



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38° 30' 



38° 00' 



37° 30' 



brate predators that rely upon bay 

 anchovy as prey. 



Because bay anchovy eggs and lar- 

 vae, and its gelatinous predators, 

 peak in abundance during summer, 

 temporally and spatially variable pre- 

 dation is potentially a significant fac- 

 tor controlling bay anchovy survival 

 and recruitment. Results of meso- 

 cosm experiments ( Cowan and Houde, 

 1993 ) have indicated that up to 20-40% 

 of bay anchovy eggs and larvae in 

 Chesapeake Bay during the peak 

 spawning season may be consumed 

 daily by jellyfish. Purcell et al. ( 1994) 

 analyzed jellyfish gut contents and 

 estimated that these predators could 

 account for up to 21'7( of the daily egg 

 mortality and 41'7f of the larval mor- 

 tality of bay anchovy in Chesapeake 

 Bay. In site-specific studies, Dorsey 

 et al. (1996) estimated that jellyfish 

 accounted for O-SS'/r/d of egg mortal- 

 ity, and from to IS'/f/d of yolksac 

 larval mortality. 



Minor variability in daily mortal- 

 ity or growth rates in a 30-50 d pe- 

 riod during early life, can generate 

 tenfold or greater differences in re- 

 cruitment potential of marine fish 

 (Gushing, 1975; Houde, 1987, 1989b). 

 Previous studies in Chesapeake Bay 

 have documented variability in an- 

 chovy egg and larval abundances and 

 yolksac larval dynamics at regional 

 scales (Dorsey et al., 1996; MacGregor 

 and Houde, 1996), but this study is 

 the first to provide a comprehensive 

 overview of larval dynamics for the entire Chesa- 

 peake Bay. At the outset, we proposed that there are 

 regional and temporal differences or patterns in 

 growth and mortality rates of bay anchovy larvae in 

 Chesapeake Bay. To test this hypothesis, we analyzed 

 otolith microstructure to estimate and compare 

 month-specific (June vs. July), and region-specific 

 (three regions) growth and mortality rates. Incre- 

 ments are deposited daily on sagittal otoliths of bay 

 anchovy, providing a record of age (Fives et al., 1986; 

 Leak and Houde, 1987; Castro and Cowen, 1991; 

 Zastrow et al., 1991). Deposition of otolith increments 

 begins on the third day after hatching and has been 

 documented in laboratory experiments (Leak and 

 Houde, 1987). Here, we discuss how regional or tem- 

 poral variability in growth and mortality might in- 

 fluence potential for recruitment and production. We 



37° 00' 



Upper 



Mid 



Lower 



77° 30' 



77° 00' 



76° 30' 



76° 00' 



75° 30' W 



Figure 1 



Chesapeake Bay. Regions, transects, and station locations for 

 ichthyoplankton samples, zooplankton samples, and CTD casts, 19- 

 22 June and 23-30 July 1993. 



compared growth and mortality rates of bay anchovy 

 larvae in relation to abundances of gelatinous preda- 

 tors and zooplankton (larval prey), and in relation 

 to salinity and temperature. Overall, our objective 

 was to determine which region(s ) of the Bay and what 

 part of the spawning season contributed most to sur- 

 vival and subsequent production of bay anchovy 

 early-life stages. 



Materials and methods 



Ichthyoplankton was collected throughout Chesa- 

 peake Bay during two baywide cruises, 19-22 June 

 and 23-30 July 1993 (Fig. 1). Forty-six stations were 

 sampled in June and 48 in July. Stations were on 15 

 transects spaced at 18.5-km ( 10 nmi) intervals from 



