COMPO\i TIONSHIPS 



Figure VIII— 2 — EFFECT OF ALEWIVES ON ZOOPLANKTON 



15 



" 10 



1942— WITHOUT ALEWIVES 



LENGTH 0- 4 



mm. 



= Cut Off 



Epischura \\ 



Yellow 

 Perch 



DOMINANT 

 ZOOPLANKTERS 



Diaptomus 



Cyclops 



16 - 



964— WITH ALEWIVES 



Leptodora 

 5 mm. 



Mesocyclops 



UPPER 

 LIMIT 



1.0 



DOMINANT 

 ZOOPLANKTERS 



The histograms show the distribution and composition of crustacean zooplankton 

 (as well as one predatory noncrustacean) before and after a population of Alosa 

 pseudoharengus (alewives) became well established. The arrows indicate the 

 size and the position in the distribution of the smallest mature instar of each 

 dominant species. Such larger zooplankton as Daphnia were present, but they 

 represented less than one percent of the total sample count. The triangles denote 

 the lower limit or cut-off point of the zooplankton consumed by the several 

 species of fish indicated. Note that with the advent of the alewives, the size 

 distribution of the zooplankton was depressed significantly to smaller species. 



229 



