Table 4. — Mean length, weight, index of fullness, number of food items per stomach, and percent frequency of 

 empty stomachs for juvenile Atlantic tomcod from Haverstraw Bay 1973-75. 



'Number of stomachs analyzed for index of fullness/total number of stomachs. 



^Two dates. 1975 only 



^1973 and 1974 



"1973-75: no index of fullness for 1973 fish. 



Table 5. — Index of fullness of 1974 juvenile Atlantic tomcod, 

 bottom water temperatures, and dissolved oxygen measure- 

 ments, Haverstraw Bay. 



were relatively abundant in trawl collections Au- 

 gust through November 1973 and 1974 (Lawler, 

 Matusky and Skelly Engineers unpubl. data). 

 Haefner (1976) found that greatest abundance of 

 C. septemspinosa in channel areas of the York 

 River and lower Chesapeake Bay occurred when 

 water temperatures were 5°-10°C and was a result 

 of migration from littoral areas to deeper, more 

 saline areas; such a temperature regime occurs in 

 Haverstraw Bay between mid-November and 

 mid- December (Figure 1). 



Feeding intensity and growth followed similar 

 seasonal patterns. Rapid growth and relatively 

 intense feeding occurred during May, June, Oc- 

 tober, and November (Table 4; Figure 3); growth 

 and feeding were depressed during July- 

 September. Prey density was not considered limit- 

 ing during summer months since Neomysis ameri- 

 cana was generally abundant. Also, resumption of 

 feeding and growth occurred during October when 

 macrozooplankton standing crop was lower than 



previous months (Lawler et al. see footnotes 5, 10, 

 11; Lauer et al. see footnote 12). Seasonally fluc- 

 tuating abiotic factors, then, may be affecting 

 growth and feeding. Food consumption in other 

 species of gadids has been observed (Tyler 1970) or 

 postulated (Sikora et al. 1972) to be inhibited at 

 temperatures >20°C. 



Tomcod are considered to have a low thermal 

 optimum (Huntsman and Sparks 1924; Bigelow 

 and Schroeder 1953; Howe 1971). Retardation of 

 growth during summer months when water tem- 

 peratures exceed 24°C has been observed in the 

 Hudson River (Lawler et al. see footnote 5; Texas 

 Instruments see footnote 7; Dew and Hecht see 

 footnote 8) and Weweantic River, Mass. (Howe 

 1971), populations. Growth of juveniles from the 

 Woods Hole area during 1962 (maximum surface 

 water temperature = 21.1°C) did not appear to 

 cease during midsummer (Lux and Nichy 1971); 

 however, only 22 young-of-the-year fish were 

 caught between June and August. 



Concomitant with elevated water temperature 

 is decreased dissolved oxygen. In separate reviews 

 of dissolved oxygen requirements, Doudoroff and 

 Shumway ( 1970) noted that feeding and growth 

 responses to low DO levels have been variable, 

 while Davis (1975) suggested that inhibition oc- 

 curred at 509c of air saturation. Warren et al. 

 (1973) found that growth and feeding of Onco- 

 rhynchus kisutch and O. tshawytscha were inhib- 

 ited when saturation was <100%, but that only a 

 10% decrease in production would occur at 70% 

 saturation. Thatcher (1975; cited in McKim et al. 

 1976) found that O. kisutch acclimated at 15°C did 

 not reduce food consumption or growth when DO 

 was >5 mg/l (49% saturation). 



Tomcod feeding, measured hy If, was minimal at 

 DO <7 mg/l during 1974; July-September percent 

 saturation ranged from 68 to 85% (Table 5). In light 



93 



