Comparison of Vertebral Counts of Atlantic Menhaden 



By 



FRED C. JUNE, Fishery Biologist (Research) 



Bureau of Commercial Fisheries Biological Laboratory 

 Beaufort, N.C. 



ABSTRACT 



Comparison was made of vertebral counts of 6,048 adult Atlantic menhaden 

 ( Brevoortia tyrannus ) collected in three localities along the Atlantic coast of the 

 United States to determine if autumn and spring spawners were distinguishable by 

 this meristic character. Two discrete groups of spawners were identified: one 

 occurring in Cape Cod and Long Island waters in spring and the other in Long Island 

 and North Carolina waters in autumn. The mean vertebral count of spring spawners 

 was 46.914 and of autumn spawners, 47.031. Lower mean counts of spring spawners 

 in 3 successive year classes were shown to be similar to those of juveniles of the 

 same year classes occupying estuarine nurseries north of Long Island, while 

 higher mean counts of autumn spawners were similar to those of juveniles occurring 

 south of Long Island. The consistency of mean vertebral counts of spring and autumn 

 spawners for 3 consecutive years suggests that the observed differences are of 

 genotypic origin. 



INTRODUCTION 



Investigation of the population structure 

 forms one phase of a progran-i of research on 

 the Atlantic menhaden ( Brevoortia tyrannus ). 

 The purposes of this phase of research are to 

 identify any natural biological units within the 

 population and to determine the overlap in 

 time and space between them. Thus far, 

 morphological characters of juveniles have 

 been compared (June, 1958; Sutherland, 1963) 

 and the distribution of spawning (Higham and 

 Nicholson, 1964; Reintjes, 1961) has been 

 studied. 



The above-mentioned studies have helped to 

 formulate hypotheses regarding population 

 structure, but there still are many unanswered 

 questions. Some of the nnore important ques- 

 tions concern the relationship of spring and 

 autumn spawners. When adults appear inshore 

 near Long Island, N.Y., and northward in 

 April or May, some are in spawning condition 

 (spawners), but the majority may be classified 

 as "spent", or otherwise sexually inactive 

 (nonspawners). The proportion of spawners 

 decreases through summer, but increases 



■■- Now with the Bureau of Sport Fisheries and Wildlife, 

 Pierre, S. Dak. 



again in September and reaches a maximum in 

 October (Higham and Nicholson, 1964). Prior 

 to their disappearance fronn northern waters 

 in October, spawners and nonspawners con- 

 gregate in large schools. These schools move 

 southward during November and congregate 

 off the North Carolina coast until mid- Decem- 

 ber (June and Nicholson, 1964). Before or 

 during the southward migration, however, the 

 composition of the schools changes, for among 

 the adult fish, only spawners appear off North 

 Carolina, and catches consisting of non- 

 spawners sometimes are taken in Long Island 

 waters immediately before and following the 

 southward nnigration of spawners. Except for 

 rare appearances, fish are absent from in- 

 shore waters through winter. In the following 

 April or May, they reappear inshore, and 

 mixed groups of spawners and nonspawners 

 again occur from Long Island northward 

 (Higham and Nicholson, 1964). 



The purpose of this study was to see if a 

 comparison of mean vertebral counts would 

 show a relationship between (1) spawners and 

 nonspawners that appear together from Long 

 Island northward in April and May, (2) spring 

 and autumn spawners in that locality, (3) 

 autumn spawners in that locality and off 

 North Carolina, and (4) spring and/or autumn 

 spawners in those localities and the juvenile 

 stocks in adjacent estuarine nurseries. 



