564 



Fishery Bulletin 97(3), 1999 



Growth rates were temporally variable, and mortal- 

 ity rates were both spatially and temporally variable. 

 It was clear that variability in these rates could sig- 

 nificantly alter production and recruitment poten- 

 tials. Baywide, larval growth rates were higher in 

 July than in June. The larval growth rates that we 

 report are higher and more variable than rates re- 

 ported previously for bay anchovy in the laboratory 



o 

 E 



s. 



0.75 



05 



0.25 



075 



05 



025 



June 



2-5 



6-9 



10-13 



>14 



July 



2-5 



6-9 10-13 



Length (mm) 



>14 



Figure 6 



Baywide mean length-specific mortality rates (/mm) 

 of bay anchovy larvae in four length classes during 

 June and Julv 1993. Error bars are =1 SE. * = no data. 



and in most field studies (Table 5). Gallagher et al. 

 ( 1983) did report equivalent and higher growth rates 

 (0.59-0.93 mm/d) in the Patuxent River tributary of 

 Chesapeake Bay. 



Temporal and spatial variability in anchovy lar- 

 val growth rates was related to both zooplankton 

 density and temperature. The mean baywide growth 

 rate of larvae increased from 0.59 mm/d in June to 

 0.72 mm/d in July, corresponding to increases in 

 mean water temperatures and mean copepod nau- 

 plii densities. The increase in larval growth rate be- 

 tween months corresponded to a coincident 1.3°C 

 increase in mean temperature at 3-m depth and to a 

 major increase in zooplankton abundance. On the 

 basis of laboratory experiments, Houde (1978) pre- 

 dicted minimal prey concentration for lO^c sui-vival 

 of bay anchovy larvae at 26" C to be 107 copepod nau- 



a 



s 1 



o 



M G M/G M G M/G 



June 



July 



Figure 7 



Baywide daily instantaneous mortality rate (M), weight- 

 specific growth rate (G). and M/G ratios for bay anchovy 

 larvae in Chesapeake Bay, June and July 1993. 



