o 



o 

 o 



o 



>- 

 o 



3 



o 



8? 



100 



80 



.. 60 



40 



20 



^ CLUPEIDS 



[^ MORONE SPP. 



^ ATLANTIC TOMCOD 



□ SAND LANCE 



□ UNIDENTIFIED FISH REMAINS 



N = 36 



i 



it 



-iii 



1973 



N = 39 



i 



Fl 



i 



I 



i 



A 



N =126 



1974 



1975 



N = 201 



P 



i 



i 



^±.„L^ 



1973- 1975 



Figure 2. — Percent frequency of occurrence offish prey categories based on number of stomachs containing identified food. 



The fact that Atlantic tomcod were found only 

 during 1973 may be due to a sampling artifact 

 because 1973 was the only year in which March 

 samples were taken, and all tomcod prey were 

 found during March 1973. In March, gravid 

 alewives, Alosa pseudoharengus , and blueback 

 herring have not yet moved into the estuary and, 

 prior to the arrival of these apparently preferred 

 prey species, Atlantic tomcod may serve as an 

 alternate forage fish. Thus the winter-spawning 

 Atlantic tomcod may be a regular diet item at a 

 time when alternate prey species are not avail- 

 able. 



It is evident from Table 1 that there are several 

 alternate fish prey for striped bass in the Hudson 

 River (e.g., blueback herring, sand lance, alewife, 

 Atlantic tomcod, white perch, and striped bass), 

 and it is expected that striped bass predation 

 upon these species would be of a compensatory 

 nature. In a simple predator-prey situation where 

 there are no alternate prey, predation is often 

 depensatory (Neave 1953) because a population of 

 predators would tend to seek out and consume a 

 high proportion of small year classes and a lower 

 proportion of strong year classes. In a more com- 

 plex community where there are several species 

 of prey, predation may be compensatory if preda- 

 tors change their feeding habits in response to the 

 availability of food (Ivlev 1961; Forney 1971). 

 That is, if several equally suitable prey species 

 were available within a system, the predator spe- 



cies would tend to feed more heavily on the most 

 abundant species, thus acting in a compensatory 

 manner. 



The ratio of white perch to striped bass in stom- 

 ach samples identified to the species level is 6:1 

 (Table 1). This ratio is based on a small sample 

 size, but it closely approximates the long-term 

 average ratio of 5.9:1 for annual CPUE values for 

 white perch and striped bass collected in several 

 hundred bottom trawls from the Haverstraw Bay 

 region (Milepoint 36) during 1971-77 (Lawler, 

 Matusky and Skelly Engineers unpubl. data). In 

 other words, yearling and older white perch and 

 yearling striped bass may be equally attrac- 

 tive prey species, and their frequency of oc- 

 currence in adult striped bass stomachs may 

 depend primarily upon the frequency of ran- 

 dom encounters rather than active prey selec- 

 tion. If this were true, the frequency of can- 

 nibalism should be greatest during those years 

 when the abundance of yearling striped bass rela- 

 tive to white perch (and other species) was great- 

 est. 



Acknowledgments 



Financial support for this project came from 

 Lawler, Matusky and Skelly Engineers; Con- 

 solidated Edison of New York; Central Hudson 

 Gas and Electric; and Orange and Rockland 

 Utilities. 



400 



