CHITTENDEN: ADULT AMERICAN SHAD IN FRESH WATER 



Bigelow and Schroeder 1953; Hildebrand 1963; 

 Leim and Scott 1966), although Holland and Yel- 

 verton (1973) reported that they occasionally take 

 large amounts offish. Atkinson (1951) attributed 

 the general absence of food in the stomachs of 

 adults to their planktonic feeding habit and the 

 absence of suitably large plankton in fresh water. 

 My observations suggest that adult shad would 

 opportunistically feed in freshwater if suitably 

 large "planktonic" forms were readily available. 



Although adults feed opportunistically in 

 fresh water, they do not regularly obtain energy 

 sufficient to maintain their weight and must use 

 energy reserves accumulated during their life at 

 sea to support migration in fresh water, final de- 

 velopment of the gonads, and spawning. Adults 

 use up their somatic substance at a size and sex 

 dependent rate of at least about 1.6-18.9 g/day. 

 Their physical activity deteriorates greatly as 

 Fowler (1908) and Walburg (1960) noted. Death 

 by starvation may occur when weight loss ex- 

 ceeds 40% (Curtis 1949), and this is probably the 

 main cause of the mortality I observed on the 

 spawning grounds. Further work is needed to 

 quantitatively describe upstream mortality, but 

 its magnitude would appear large as Bean (1892, 

 1903) and Anonymous (1902) also observed in the 

 Delaware River and Walburg (1960) observed in 

 the St. Johns River, Fla. 



Weight loss was related to sex and size in 

 agreement with Leggett (1972). The apparent re- 

 lationship between weight loss and sex, however, 

 may not be direct. Metabolic rate, in general, in- 

 creases with temperature within limits. Leggett 

 (1972) noted that females tend to migrate later 

 and at a higher temperature than males and 

 suggested that temperature was responsible for 

 the apparent sex difference in weight loss. The 

 relationship between size and total metabolism in 

 a wide variety of organisms can be expressed as: 



log M = \oga + b \ogW 



where M is total metabolism and W is weight 

 (Paloheimo and Dickie 1966; Prosser 1973). The 

 relationship between metabolic rate and size can 

 be expressed (Prosser 1973) as: 



log M/W = log a + (6 - 1) log W. 



From the latter expression it follows that a b 

 value less than 1.0 implies that the metabolic rate 

 decreases with increasing size, while a b value 



greater than 1.0 indicates that the metabolic rate 

 increases with size. The value generally found for 

 b is about 0.8 (Paloheimo and Dickie 1966; Pros- 

 ser 1973), although Fry (1971) cautions that this 

 value should not yet be accepted as dogma. Pres- 

 ent findings on the relationship between size and 

 weight loss in shad on their spawning migration 

 are consistent with a b value greater than 1.0. 

 Calculations made herein obviously assume that 

 adult fish of all sizes are in fresh water the same 

 length of time. If 6 is not greater than 1.0, we 

 must conclude that: 1) small adults enter fresh 

 water later than large fish and thus are in fresh 

 water for a shorter period of time, or 2) small fish 

 make better use of available freshwater food 

 resources. 



Estimates of the time that adults can remain in 

 fresh water suggest that only small fish can sur- 

 vive upstream into the fall. The small fish I cap- 

 tured in the James River in October apparently 

 had lost only about 33-39% of its weight in com- 

 parison with the Delaware River somatic weight 

 regression at Lambertville and an unusually 

 small fish (285 mm FL, 288 g) captured at Lam- 

 bertville. It is noteworthy that, except for 

 Nichols' (1959) report of a 430 mm FL male, the 

 adult shad reported in fresh water during the fall 

 have all been males about 305 mm long. Fish this 

 small, however, are rare in the age compositions 

 reported from many Atlantic Coast rivers (Talbot 

 1954; Fredin 1954; Walburg 1956, 1957, 1960, 

 1961; Sykes 1956; Sykes and Lehman 1957; Wal- 

 burg and Sykes 1957; La Pointe 1958; Nichols and 

 Tagatz 1960; Nichols and Massmann 1963; God- 

 win 1968; Leggett 1969; Chittenden 1975). 



ACKNOWLEDGMENTS 



For assisting in field collections, I am deeply 

 grateful to J. Westman, J. Hoff, J. Harakal, D. 

 Riemer, J. Barker, F. Bolton, R. Coluntuno, K. 

 Compton, R. Gross, C. Masser, R. Stewart, J. 

 Miletich, S. Hoyt, L. Schulman, H. Dinje, H. 

 Buckley, J. Musick, M. Bender, J. Gift, C. 

 Townsend, R. Bogaczk, and K. Marcellus of or 

 formerly of Rutgers University, Harvard Univer- 

 sity, New Jersey Division of Fish and Game, and 

 New York Department of Environmental Con- 

 servation. 



Fred and William Lewis, Jr. generously gave 

 permission to collect shad at their fishery at 

 Lambertville and frequently assisted in seining. 

 J. D. McEachran and W H. Neill of Texas A&M 



155 



