Comparative Study of Juvenile American Shad 

 Populations by Fin Ray and Scute Counts 



By 



PAUL R. NICHOLS, Fishery Biologist (Research) 



Bureau of Commercial Fisheries Biological Laboratory 

 Beaufort, N.C. 



ABSTRACT 



Forty-five juvenile American shad, Alosa sapidissima (Wilson), collections, 

 from 10 major shad producing rivers along the Atlantic coast of North America, 

 were examined to see if differences in meristic counts suggested evidence of 

 discrete river populations. Four meristic characters — pectoral, dorsal, and anal 

 fin rays and scutes--were used. The difference in the counts between locations and 

 between years within rivers 'was small compared to that between rivers. The differ- 

 ences in counts between rivers indicated that discrete populations of juvenile shad 

 occurred in rivers. 



INTRODUCTION 



In studies to discover causes of the de- 

 cline in yield of American shad, Alosa sap- 

 idissima (Wilson), and to determine factors 

 favoring recovery of the fishery, it was 

 essential that the number and distribution of 

 populations be known. 



The shad is widely distributed along the 

 Atlantic coast from the St. Lawrence River, 

 Canada, to the St. Johns River, Fla. This 

 species is anadromous, spending most of its 

 life in the ocean, but ascending coastal rivers 

 to spawn. The spawning migrations into the 

 rivers begin earliest in the southern part of 

 the range (November in St. Johns River, Fla.) 

 and are progressively later northward (June 

 in St. John River, Canada). A female spawns 

 about 250,000 eggs, and hatching occurs in 

 6 to 8 days at a water temperature of 17° C. 

 The young shad stay in the rivers until autumn, 

 attaining a length ranging from 75 to 145mm., 

 and then migrate to sea. After spending from 

 2 to 6 years in the ocean, shad return to the 

 rivers to spawn. Those spawning in rivers 

 south of Cape Hatteras, N.C, normally die 

 after spawning, while north of Cape Hatteras 

 the proportion of fish spawning for the second 

 time or more progressively increases from 

 about 15 to 25 percent in Chesapeake Bay 

 tributaries to about 45 to 55 percent in the 

 Connecticut River. 



Several workers have reported evidence of 

 different shad populations along the Atlantic 

 coast. Differences between shad from different 

 areas based on meristic counts (Fischler, 

 1959; Hildebrand and Schroeder, 1928; Hill, 



1959; Vladykov and Wallace, 1938), growth 

 rates (Hammer, 1942; - 1 Hildebrand and 

 Schroeder, 1928), and fecundity (Davis, 1957; 

 Lehman, 1953) indicated the occurrence of 

 different populations. Recapture on the spawn- 

 ing ground of shad tagged in prior seasons 

 indicated that they returned to their native 

 streams to spawn (Hollis, 1948; Nichols, I960). 

 Also, the fact that the runs in the northern 

 rivers -were self-perpetuating and fluctuated 

 independently (Talbot and Sykes, 1958) sug- 

 gested different populations. 



The purpose of this study was to determine 

 if discrete populations of shad could be iden- 

 tified on the basis of consistent differences 

 in counts of meristic characters in juveniles 

 from 10 rivers. As used in this report, a 

 "population" is a group of fish having similar 

 meristic characteristics, of which the nature 

 of origin, genotypic and/or phenotypic, of the 

 characteristics has not been determined. 



MATERIALS AND METHODS 



For this study, the Atlantic coast was di- 

 vided into three geographical areas: North 

 Atlantic (Maine to Virginia); Chesapeake Bay 

 (Maryland and Virginia); and South Atlantic 

 (North Carolina to Florida). In 10 major shad 

 producing rivers within these areas, 45 col- 

 lections of juvenile shad, from 43 to 146 mm. 

 fork length, were taken near spawning and 



■""The homing instinct of the Chesapeake Bay shad, 

 Alosa sapidissima (Wilson), as revealed by a study of their 

 scales. Thesis (typewritten), 1942, University of Maryland, 

 45 p. 



