Jung and Houde: Recruitment and spawning-stock biomass distribution of Anchoa mitchil/i 75 



Early-stage and larvae 



Density-compensatory 



Prey is smaller 



Small scale (1 m-10 km) 



Densiy of early-stage larvae 

 (1 m-10 m scale) 



Late-stage larvae and juveniles 

 Density-depensatory 

 Predator is bigger 

 Mesoscale(IO-lOOkm) 



Recruits 



Ontogenetic migration 



Densiy of late-stage larvae 

 (10-100 km scale) 



SSB 



Figure 7 



Hypotheses and conceptual model of the bay anchovy {Anchoa mitchilli) recruitment process in 

 Chesapeake Bay. The density-compensatory process acts at a small spatial scale during the early- 

 larval stages, whereas the density-depensatory process acts at a broader spatial scale during late-stage 

 larval and juvenile stages. The ontogenetic migration is controlled by dissolved oxygen levels and other 

 hydrological factors. 



1994), but their potential role with respect to bay anchovy 

 recruitment could not be defined in our study. For the 

 present, it is clear that most spawning occurs in the lower 

 and mid Chesapeake Bay, from which larval and juvenile 

 anchovies disperse upbay. We hypothesize that food avail- 

 ability is the major factor controlling production of bay 

 anchovy early-larval stages whereas predation becomes 

 more important during late-larval and juvenile stages. 

 Our results and hypotheses implicate density-related pro- 

 cesses, operating at different spatial scales, as regulators 

 of recruitment of bay anchovy in Chesapeake Bay. 



Acknowledgments 



We thank S. Leach, E. North, J. Hagy, C. Rilling, J. Cleve- 

 land, A. Madden, D. O'Brien, B. Pearson, D. Craige, T. Auth, 

 and the able crew of RV Cape Henlopen for assistance in 

 field surveys. T. Miller and E. Russek-Cohen provided com- 

 ments and assistance on statistical analyses. This research 

 was supported by a U.S. National Science Foundation, Land 

 Margin Ecosystem Research (LMER) program grant, 

 "Trophic interactions in estuarine systems (TIES)" (grant 

 DEB94-12113). Additional support was provided by NSF 

 Grant OCE-9521512 and by National Oceanic and Atmo- 

 spheric Administration grant NOAA, NA170P2656. 



Literature cited 



Able, K. W„ and M. P. Fahay. 



1998. The first year in the life of estuarine fishes in the 



Middle Atlantic Bight. 342 p. Rutgers Univ. Press, New 

 Brunswick, NJ. 

 Alheit, J. 



1987. Egg cannibalism versus egg predation: their signifi- 

 cance in anchovies. S. Afr. J. Mar. Sci. 5:467-470. 

 Bailey. K. M., and E. D. Houde. 



1989. Predation on eggs and larvae of marine fishes and the 

 recruitment problem. Adv. Mar. Bio. 25:1-83. 

 Baird, D.. and R. E. Ulanowicz. 



1989. The seasonal dynamics of the Chesapeake Bay 

 ecosystem. Ecol. Monogr. 59:329-364. 

 Belsley, D. A., E. Kuh, and R. E. Welsch. 



1980. Regression diagnostics: identifying influential data 

 and sources of collinearity, 292 p. John Wiley and Sons, 

 Inc., New York, NY. 

 Bhattacharya, C. G. 



1967. A simple method of resolution of a distribution into 

 Gaussian components. Biometrics 23:115-135. 

 Breitburg, D. L. 



1992. Episodic hypoxia in Chesapeake Bay: Interacting 

 effects of recruitment, behavior, and physical disturbance. 

 Ecol. Monogr. 62:525-546. 

 Cowan, J. H., K. A. Rose, E. D. Houde, S. B. Wang, and J. Young. 

 1999. Modeling effects of increased larval mortality on bay 

 anchovy population dynamics in the mesohaline Chesa- 

 peake Bay: evidence for compensatory reserve. Mar. Ecol. 

 Prog. Ser. 185:133-146. 

 Cronin. W. B. 



1971. Volumetric, areal, and tidal statistics of the Chesa- 

 peake bay estuary and its tributaries, 15 p. Chesapeake 

 Bay Institute, Johns Hopkins Univ., Baltimore, MD. 

 Dorsey, S. E., E. D. Houde. and J. C. Gamble. 



1996. Cohort abundances and daily variability in mortality 

 of eggs and yolk-sac larvae of bay anchovy, Anchoa mitchilli, 

 in Chesapeake Bay. Fish. Bull. 94:257-267. 



