dock, Melanogrammus aegleftnus L. Biol. Bull. (Woods 

 Hole) 141:176-188. 

 STEEN, J. B. 



1970. The swimbladder as a hydrostatic organ. In W S. 

 Hoar and D. J. Randall (editors), Fish physiology, Vol. 

 IV, p. 413-443. Acad. Press, N.Y. 

 Tait.J.S. 



1960. The first filling of the swim bladder in salmonoids. 

 Can. J. Zool. 38:179-187. 



Table l. — Collections of age 1 and 2 Atlantic tomcod from 

 Haverstraw Bay, Hudson River, 1973-76. 



James S. bulak 



Fisheries Research Laboratory and Department of Zoology 

 Southern Illinois University, Carbondale, III. 

 Present address: South Carolina Wildlife and 

 Marine Resources Department 

 P.O. Boxl70,Bonneau. SC 29431 



RoyC. Heidinger 



Fisheries Research Laboratory and Department of Zoology 

 Southern Illinois University 

 Carbondale, IL 62901 



FOOD OF AGE 1 AND 2 ATLANTIC TOMCOD, 



MICROGADUS TOMCOD, FROM HAVERSTRAW 



BAY, HUDSON RIVER, NEW YORK 



Atlantic tomcod, Microgadus tomcod (Walbaum), 

 are opportunistic fee(iers (Howe 1971; Grabe 

 1978) with amphipods Gammarus spp. and the 

 decapod Crangon septemspinosa identified as 

 primary prey (Howe 1971; Alexander 1971; Scott 

 and Grossman 1973; Grabe 1978; NittelM. Lim- 

 ited data are available on the biology of year- 

 ling and older Hudson River tomcod due to their 

 low overall abundance and because they are most 

 abundant during winter when ice cover restricts 

 sampling. This note summarizes feeding data of 

 339 tomcod, ages 1 and 2, from the Haverstraw 

 Bay area of the Hudson River (37.5-41.5 mi north 

 of the Battery, New York City) on 19 dates, 

 January 1973- June 1976, and supplements food 

 preference data on juveniles (Grabe 1978). All 

 fish were collected as part of an ecological 

 monitoring program conducted by Lawler, 

 Matusky & Skelly Engineers for Orange and 

 Rockland Utilities, Inc. 



Methods 

 Collections (Table 1) were made with a 9.1 m 



otter trawl (64 mm mesh cod end liner) towed 

 against the tide at 1.5-2.0 m/s during both day 

 and night. The data are likely to be biased to- 

 wards daytime feeding preferences since almost 

 twice as many tows were taken during daytime as 

 at night. Diel differences in feeding could not be 

 evaluated because day and night collections were 

 often combined for other analyses. Fish were pre- 

 served in 10% buffered Formalin.^ In the labora- 

 tory they were measured ( ± 1 mm total length, TL) 

 and weighed (±0.1 g), and the stomachs were 

 removed and preserved in 70% ethanol. Prey 

 were identified and counted, and the contents of 

 195 stomachs were dried at 103° C. The number of 

 fish per sampling period whose stomach contents 

 were analyzed were limited by contract and were 

 randomly selected from the total catch. Whenever 

 possible, I analyzed additional fish to increase 

 both sample size and temporal coverage. Yearling 

 and older tomcod collected during fall 1973 were 

 separated from young-of-the-year by examination 

 of length-frequency histograms drawn from 

 larger samples (Lawler, Matusky & Skelly En- 

 gineers^); by this method age 1 and 2 fish were 

 those 3^160 mm TL. On other sampling dates 

 young-of-the-year were present only as larvae or 

 as juveniles < 1 10 mm TL. 



Food preference data were classified seasonally 

 and examined as percentage occurrence (number 

 of fish in which prey item "a" occurred/total 

 number offish), percentage composition (number 

 of prey item "a'Vtotal number of prey), and as im- 

 portance, I, the geometric mean of these two mea- 

 surements (Windell 1971). This approach, how- 

 ever, may overestimate the utilization of smaller 

 prey (e.g., copepods) but should provide a better 

 indication of feeding preference than either per- 

 cent occurrence or percent composition taken 

 singly. An index of fullness (Windell 1971), If, 

 was calculated to evaluate feeding intensity (dry 



'Nittel, M. 1976. Food habits of Atlantic tomcod Mi- 

 crogadus tomcod) in the Hudson River. In Hudson River 

 Ecology. Fourth Symposium on Hudson River Ecology. Bear 

 Mountain, NY., March 28-30 1976. Hudson River Environmen- 

 tal Society, Inc. 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



^Lawler, Matusky & Skelly Engineers. 1976. Environ- 

 mental impact assessment — water quality analysis: Hudson 

 River. Natl Comm on Water Quality. NTIS PB-251099, 



FISHERY BULLETIN: VOL 77. NO, 4. 1980 



1003 



