792 



Fishery Bulletin 91(4), 1993 



I PRESENT STUDY 

 (1987-1988) 

 j PREVIOUS STUDIES 

 ! (1972-1978) 



O 

 <r 



UJ 

 00 



5 



LOWER RIVER 



MO- RIVER 



RIVER REGION 



Figure 2 



Number of ichthyoplankton taxa found in each of the three 

 regions of the tidal Delaware River in the present ( 1987- 

 1988 1 and in previous ( 1972-1978 ) studies. 



g 350 



UJ 



300 



O 



00 250 



o 



o 200 



oo 



z 



I PRESENT STUDY 

 (1967-1988) 



 PREVIOUS STUDIES 

 I (1972-1978) 



LOWER RIVER 



MI-RIVER 



RIVER REGION 



UPPER RIVER 



Figure 3 



Average ichthyoplankton density (#/1000 m'l in each of the 

 three regions of the tidal Delaware River in the present (1987- 

 1988) and in previous (1972-1978) studies. 



A. sapadissima, M. americana, and Alosa spp., occurred 

 at average densities greater than 10/100 m :) in either 

 the mainstem or the tributaries. 



Numbers of taxa did not differ significantly among 

 the three regions of the river (Fig. 2), but average 



ichthyoplankton density did <P<0.001) (Fig. 3). Den- 

 sity was greatest in the upper region (between the 

 Schuylkill River and Trenton, NJ) where it averaged 

 more than 120 larvae/100 m :l during the study. In con- 

 trast, density in the mid-river region (between Phila- 



