Table 2. — Monthly summary of five most important food items 

 of juvenile Atlantic tomcod from Haverstraw Bay, 1973-75. 



Month 



Sample 

 size 



Taxon 



Percent Percent 

 occur- compo- 

 rence sition 



May 



38 



June 



210 



July 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



69 



58 



43 



43 



42 



74 



Index 



Table 3. — Importance values of copepods, amphipods, and 

 Neomysis americana in stomachs of June and July juvenile At- 

 lantic tomcod pooled by 10-mm size intervals. 



FISHERY BULLETIN: VOL. 76, NO. 1 



DISCUSSION 



Howe (1971) characterized tomcod as opportun- 

 istic feeders; the data presented here qualify that 

 hypothesis. Smaller tomcod, present during May 

 and June, preyed upon copepods (Table 2) which 

 have been the most abundant zooplankters col- 

 lected by 76- and 150-/Lim mesh nets in this reach of 

 the Hudson River (Lawleretal. see footnotes 5, 10; 

 Lawler et al.i\ Lauer et al.^^). When total length 

 reached 80-90 mm (June- July), food preference 

 shifted to larger prey, e.g., amphipods (Table 3). 

 Such a shift has been documented in a variety of 

 species (Nikolsky 1963; Stickney et al. 1974; 

 Werner 1974; Stickney 1976), including the re- 

 lated species Gadus morhua (Kohler and Fitz- 

 gerald 1969). This shift did not appear to be a 

 response to changes in prey density, since abun- 

 dance of copepods increased while that of amphi- 

 pods decreased during June-August 1973-75 

 (Lawler et al. see footnotes 5, 10, 11). 



Copepods were a supplementary prey during 

 December, occurring as frequently as the larger 

 decapods Crangon septemspinosa (5.4%) and 

 Rhithropanopeus harrisii (4.1%) which were rela- 

 tively important during November (Table 2). 

 Selection of smaller prey with the concomitant 

 decrease of larger prey may be a response to the 

 constriction of the alimentary canal by maturing 

 gonads noted by Schaner and Sherman ( 1960). In 

 Hudson River tomcod, gonadal biomass prior to 

 spawning averages between 15 (males) and >30% 

 (females) of the body weight minus the gonad 

 weight. In contrast, female gonads in Hudson 

 River Morone americana (Lawler et al. see foot- 

 note 10) average about 8%, Alosa sapidissima 

 about 22% (calculated from Lehman 1953), Tri- 

 nectes maculatus less than 6% (calculated from 

 Koski 1974), while those of Tautogolabrus adsper- 

 sus from Long Island Sound averaged about 7% 

 (Dew 1976) of the body weight minus the gonad 

 weight. 



A decrease in prey (C. septemspinosa) avail- 

 ability was not considered a factor in this change. 

 In the Haverstraw Bay area, C septemspinosa 



effects of temperature from those of dissolved oxy- 

 gen were not applied since the two parameters 

 were highly correlated (r = -0.96). If was, how- 

 ever, lowest when water temperatures were 

 >24°C and dissolved oxygen (DO) <7 mg/1 and 

 increased at temperatures <19°C and DO >7 mg/1 

 (Table 5). 



"Lawler, Matusky and Skelly Engineers. 1976. 1975 Hudson 

 River aquatic ecology studies: Bowline Point and Lovett 

 Generating Stations. Prepared for Orange and Rockland 

 Utilities, Inc. 



i^Lauer, G. J., W. T. Waller, D. W. Bath, W. Meeks, R. Heffner, 

 T. Ginn, L. Zubarik, P. Bibko, and P. C. Storm. 1974. Entrain- 

 ment studies on Hudson River organisms. In L. D. Jensen 

 (editor). Proceedings of the second entrainment and intake 

 screening workshop, Feb. 5-9, 1973, p. 37-88. Johns Hopkins 

 Univ., Baltimore, Md. 



92 



