FISHERY BULLETIN: VOL. 73, NO. 3 



spawning migration at age IV and females at age 

 V, the strongly male dominated runs of 1961 and 

 1962 reflect the entry of unusually large year 

 classes into the fishery. The magnitude of the 

 spawning runs declined greatly after 1963, and the 

 shift towards female dominance reflects the 

 failure of new year classes to be recruited. The 

 strength of the 1962, 1963, and 1964 year classes as 

 defined was small because the 1966 to 1968 runs 

 were very small. Yet, from visual observations and 

 collections of young during the summer, Chitten- 

 den (1969) concluded that strong year classes were 

 produced throughout the period 1962-66. I 

 presented dissolved oxygen data for the periods 

 when the young passed the Philadelphia area each 

 year and ascribed the failure of these strong year 

 classes to later recruit to the fishery to cata- 

 strophic destruction of the young as they passed 

 through the grossly polluted area. 



There was a negligible percentage of repeat 

 spawners in the Delaware River American shad 

 runs from 1963 to 1965, and there were no repeat 

 spawners among 245 American shad collected 

 from the 1961 run (J. Malcolm, pers. commun.). The 

 existence of numerically few repeat spawners 

 must have continued to be the case after 1965 

 because the runs from 1966 to 1968 were very 

 small. Delaware River runs apparently have 

 included few repeat spawners for at least some 25 

 yr because Sykes and Lehman (1957) reported that 

 less than 2% of 423 fish captured in 1944, 1945, 1947, 

 and 1952 were repeat spawners. Even the produc- 

 tion of very large year classes appears to have 

 little effect on the percentage of repeat spawners 

 in the Delaware River. The percentage was only 

 6.5% in 1965, a year when the very strong 1958 and 

 1959 year classes should have increased the per- 

 centage greatly rather than by only a few points. 

 As Sykes and Lehman (1957) pointed out, the vir- 

 tual absence of repeat spawners in the Delaware 

 River is very unlike that in other middle-North 

 Atlantic coast rivers where repeat spawner per- 

 centages have been: St. Johns River, N.B., Canada, 

 22-81% (Leggett 1969); Connecticut River, 14-60% 

 (Moss 1946; Nichols and Tagatz 1960; Leggett 

 1969); Hudson River, 51% (Talbot 1954); 

 Susquehanna River, 37% (La Pointe 1958); Po- 

 tomac River, 17% (Walburg and Sykes 1957); York 

 River, 21-27% (Nichols and Massmann 1963; Leg- 

 gett 1969); James River, 27%, (Walburg and Sykes 

 1957). Some of the higher percentages of repeat 

 spawners in these rivers are undoubtedly biased 

 towards the high side because they are based on 



collections of fish from hightly selective commercial 

 gill nets. However, it appears that the Delaware 

 River has a much lower percentage of repeat 

 spawners. The Delaware River seems most like 

 rivers south of Cape Hatteras, N.C., where few 

 repeat spawners have been reported: Neuse River, 

 less than 3% (La Pointe 1958; Walburg 1957); 

 Edisto River, 0% (Walburg 1956); Ogeechee River, 

 0% (Sykes 1956); Altamaha River, 0% (Godwin and 

 McBay 1967; Godwin 1968); St. Jones River, Fla., 

 0% (Walburg 1960; Leggett 1969). 



Age-class structures of American shad runs 

 have been reported by many workers including 

 Talbot (1954), Fredin (1954), Walburg (1956, 1957, 

 1960, 1961), Walburg and Sykes (1957), Sykes 

 (1956), La Pointe (1958), Nichols and Tagatz (1960), 

 Nichols and Massmann (1963), Godwin (1968), and 

 Leggett (1969). Walburg and Nichols (1967) sum- 

 marized the available information by stating that 

 age IV and V fish make up the bulk of the catch in 

 South Atlantic rivers and Chesapeake Bay tribu- 

 taries while the catch is primarily composed of age 

 IV to VII fish in middle Atlantic rivers. Delaware 

 River runs in the 1960's were primarily supported 

 by age IV and V fish, although age VI females 

 were also important. Sykes and Lehman (1957) 

 reported similar findings for fish collected in the 

 1940's and 1952 except that they gave more weight 

 to age VI fish, possibly due to sampling with com- 

 mercial gill nets. 



Because of the absence of repeat spawners, 

 which tend to be older fish, few age-groups support 

 American shad runs in the Delaware River. This is 

 similar to the situation in South Atlantic rivers but 

 unlike that in North Atlantic rivers. The apparent 

 similarity of Delaware River American shad to 

 those of southern rivers rather than to 

 geographically more closely related fish from 

 northern rivers is an artifact caused by man. 

 Howell (1837) reported that American shad cap- 

 tured in the Delaware River averaged about 3,175 

 g (7.00 pounds). In contrast, Chittenden (1969) 

 reported that males averaged 1,107 g (2.44 pounds) 

 with 95% confidence limits about the mean being 

 1,080-1,134 g (2.38-2.50 pounds) and females 

 averaged 1,737 g (3.83 pounds) with the 95% con- 

 fidence limits being 1,701-1,774 g (3.75-3.91 

 pounds). The older age-classes obviously present in 

 Howell's time are now absent, primarily due to 

 pollution and fishing activities. Sykes and Lehman 

 (1957) and Chittenden (1969) attributed the virtual 

 absence of repeat spawners to mortality of adults 

 in low oxygen water near Philadelphia as they 



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