Jung and Houde: Recruitment and spawning-stock biomass distribution of Anchoa mitchilli 



71 



Zl 39°00' 



38°00' 



CO 

 CO 

 CO 



37°00' 



April-May 

 June-August 



400 500 600 700 



Mean river flow from June to Feb (m 3 /sec) 



1995 

 1996^ 



1999 



1998 



37°00' 



2000 



1997 



Y= 35.78 + 0.53 A' 

 r 2 =0.75(p=0.02) 



3.0 3.5 4.0 4.5 5.0 



Dissolved oxygen (mg/L) 



5.5 



Figure 3 



Mean location (latitude) of adult bay anchovy {Anchoa mitchilli) spawn- 

 ing stock biomass (SSB) in Chesapeake Bay. (A) Mean latitude and 

 standard deviation in April-May and in June-August. The upper verti- 

 cal bar represents mean + standard deviation for June-August, and the 

 lower vertical bar represents mean-standard deviation for April-May, 

 I B l Mean latitude in April-May and mean Susquehanna River flow from 

 June of the previous year to February of the current year. (C) Mean lati- 

 tude in June-August and mean dissolved oxygen in the subpycnocline 

 layer of the middle bay in June-August. 



processes were important and high adult SSB could pro- 

 duce abundant first-feeding larvae with subsequent den- 

 sity-dependent food competition. In Tampa Bay, Florida, 

 Peebles et al. ( 1996) hypothesized that bay anchovy's size- 

 specific fecundity is directly related to prey availability 

 for adults. Modeled results of Rose et al. (1999) suggested 

 that density-dependent growth of bay anchovy larvae and 

 juveniles in Chesapeake Bay would lead to density-depen- 

 dent survival of these stages. Hunter and Kimbrell (1980) 

 and Alheit (1987) proposed that cannibalism by adults on 



eggs and larvae provides a degree of density-dependent 

 regulation in anchovies of the genus Engraulis. Analyses 

 of feeding by adult bay anchovy did not indicate that pe- 

 lagic fish eggs were a significant part of bay anchovy diet 

 (Vazquez-Rojas, 1989; Klebasko, 1991), although no specific 

 study of cannibalism has been undertaken. 



We propose three hypotheses that may explain the rela- 

 tionships among regional DO concentration, the latitudi- 

 nal shift in SSB distribution during the spawning season 

 (AL), and recruitment levels of bay anchovy in October. The 



