DYNAMICS OF AMERICAN SHAD, ALOSA SAPIDISSIMA, RUNS 



IN THE DELAWARE RIVER' 



Mark E. Chittenden, Jb.^ 



ABSTRACT 



Adult American shad were collected by haul seining at regular intervals during the spring migrations 

 from 1963 to 1965 and by collecting specimens from a fishkill in spring 1965. Supplementary sex and size 

 composition data were obtained from summer rotenone sampling in 1961 and 1962. 



Males tended to precede females in the spring run. Annual sex compositions were strongly male 

 dominated from 1961 to 1963 and were strongly female dominated in 1964 and 1965. Repeat spawners 

 composed 2.6% of 729 fish examined from 1963 to 1965. Age I and II fish were absent or virtually absent 

 from the run. Males migrated upstream primarily at age IV and females at age V. Large runs during 

 the early 1960's were based on the 1958 and 1959 year classes as defined which were much larger than 

 other year classes produced in the period 1957-64. Delaware River American shad runs now have little 

 buffering against fluctuations in abundance because few year classes are successful, few age groups 

 support the run, and there are essentially no repeat spawners. Larger runs in the Delaware since 1925 

 and probably somewhat earlier, in general, were apparently based on one large year class and essen- 

 tially no repeat spawners. 



The American shad, Alosa sapidissima, formerly 

 was one of the most abundant anadromous fishes 

 in the United States where more than 50 million 

 pounds were landed in 1896. In contrast, only 8 

 million pounds were caught in 1960 (Walburg and 

 Nichols 1967). Much of this decline is due to the 

 collapse of the Delaware River Basin fisheries 

 which once supported larger landings of American 

 shad than any other river system (Stevenson 

 1899). Estimates of the 1896 Delaware Basin catch 

 are about 16.5 to 19.2 million pounds (Smith 1898; 

 Sykes and Lehman 1957; Walburg and Nichols 

 1967)-about a third of the national total. Annual 

 Delaware Basin catches about that time varied 

 from 14 to 17 million pounds and were probably 

 primarily fish of Delaware River origin (Chitten- 

 den 1974). In contrast, annual Delaware Basin 

 landings since 1920 have consistently been much 

 less than 0.5 million pounds (Sykes and Lehman 

 1957; Chittenden 1974). 



Trends in abundance of Delaware Basin stocks 

 have been described by Sykes and Lehman (1957) 

 and Chittenden (1974), and causes of these fluc- 

 tuations have been described by Ellis et al. (1947), 

 Sykes and Lehman (1957), Walburg and Nichols 



'Based on part of a dissertation submitted in partial fulfillment 

 of the reauirements for PhD degree, Rutgers University, New 

 BrunswicK, N.J. 



'Department of Wildlife and Fisheries Sciences, Texas A & M 

 University, College Station, TX 77840. 



Manuscript accepted October 1974. 

 FISHERY BULLETIN: VOL. 73, NO. 3, 1975. 



(1967), and Chittenden (1969). The dominant fac- 

 tor affecting abundance during the past 60 yr, at 

 least, has been pollution near Philadelphia, Pa. 

 Complete understanding of the causes of fluctua- 

 tions in abundance, however, depends on detailed 

 knowledge of the population dynamics of this 

 species. Many workers have described certain as- 

 pects of the population dynamics of American 

 shad in other river systems. Little work has been 

 published for the Delaware, in part because 

 Delaware River American shad stocks have been 

 so low that it has been difficult to collect large 

 numbers of fish. 



The present paper describes data collected on 

 sex, size, age, and repeat spawner composition; 

 comparative magnitudes of American shad runs; 

 and year-class strengths in the Delaware River 

 during the late 1950's and the 1960's. 



MATERIALS AND METHODS 



Adult fish were collected 22.5 km (14 miles) 

 above tidal water in the years 1963 to 1965 at the 

 site of the Lewis Fishery in Lambertville, N.J., 

 using a 76-mm (3-inch) stretch-mesh, 107-m (350- 

 foot) long and 3.6-m (12-foot) deep (4.3 m = 14 feet 

 in 1963) haul seine that was paid out from a boat 

 and landed about 396 m (1,300 feet) downstream. 

 Sampling occurred at 4-day intervals after a ran- 

 domly selected date in 1963 but at fixed intervals 



487 



