There also appears to be a consistent difference 

 in the relative abundance of the two spawning 

 groups. Higham and Nicholson (1964), for 

 example, showed that from Long Island north- 

 ward, somewhere between 12 and ISpercentof 

 the fish in purse seine catches in October 1958, 

 1959, and I960 were sexually inactive. In the 

 present study, the proportion of spring 

 spawners in individual samples collected in 

 these samie waters in May was between 13 and 

 ZO percent of about the same total numbers of 

 fish caught in each corresponding October. The 

 relatively small numbers of nonspawners in the 

 autumn catches and spring spawners in spring 

 catches north of Long Island indicate that 

 spring spawners probably constituted a much 

 snnaller group than autumn spawners. 



The similarity in the vertebral counts of 

 juveniles in northern estuaries and of spring 

 spawners from adjacent ocean waters further 

 emphasizes the distinctness of a northern group 

 of fish which appears to be physiologically 

 and genetically adapted to life under conditions 

 of lower temperature. Thus, the inverse re- 

 lation between vertebral number and tennper- 

 ature noted for many clupeoid fishes (Barlow, 

 1961) does not seenn to hold for Atlantic men- 

 haden. 



In the present study, the hypothesis was that 

 no more than two discrete groups of spa%vners 

 were present simultaneously in the different 

 localities, and the data confirm that this con- 

 clusion, in general, agrees with the known 

 facts concerning the occurrence of spring- and 

 autumn- spawned juveniles in estuarine 

 nurseries and the seasonal occurrence of 

 sexually active fish in the commercial catches. 

 Sonne spawning, however, occurs in waters 

 north of Long Island through sunnmer (Herman, 

 1963). Furthermore, spawning by younger, 

 smaller fishoccurs from North Carolina south- 

 ward beginning in September or October (in 

 advance of the arrival of the larger, older 

 spawning fish from farther northward). The 

 relationship of these additional spawning groups 

 should be investigated as soon as practicable 

 since they must be considered in answering 

 the question of population structure. 



In view of the results of this study, I 

 recomnnend that the meristic studies be ex- 

 panded to include all known spawning groups. 

 Other meristic and/or morphometric 

 characters also should be included to 

 provide estimates of the relative proportions 

 of discrete subpopulation components in mixed 

 samples of fish. Growth, serological, and 

 fecundity studies also should be undertaken 

 since these will yieldr ancillary information 

 that, when combined with results of meristic 

 studies, might lead to an understanding of the 

 structure of the Atlantic menhaden population. 



SUMMARY 



1. Vertebral counts of 6,048 adult Atlantic 

 menhaden ( Brevoortia tyr annus ) collected off 

 Cape Cod, Mass., Long Island, N.Y., and 

 Beaufort, N.C., from 1957 to 1960 were analyzed 

 to determine if autumn (October-December) 

 and spring (April-May) spawners were dis- 

 tinguishable by this meristic character. 



2. Variation between sexes and within and 

 between year classes was found to be negligible. 



3. Two discrete groups of spawners--one 

 occurring in Cape Cod and Long Island waters 

 in spring and the other occurring in Long Is- 

 land and North Carolina waters in autumn- - 

 were identified on the basis of mean vertebral 

 count. The mean count of spring spawners 

 was 46.914, and of autum spawners, 47.031, 



4. Comparison of mean counts of spawners 

 in three successive year classes (1955-57) 

 with those of juveniles in the same year 

 classes from estuarine nurseries showed that 

 lower mean counts were associated with spring 

 spawning north of Long Island. 



5. The tendency for mean vertebral counts 

 of reproductively isolated groups to follow a 

 distinct pattern for several years suggests that 

 the observed differences are genotypic in 

 origin. 



ACKNOWLEDGMENTS 



Doyle F. Sutherland, with James F. Guthrie, 

 collected most of the specimens and made the 

 vertebral counts and measurements upon which 

 this study was based. Joseph R. Highann, Jr. 

 aged the fish. 



LITERATURE CITED 



BARLOW, GEORGE W. 



1961. Causes and significance of morpho- 

 logical variation in fishes. Syst. Zool. 



10 (3): 105-117. 

 BUMPUS, DEAN F. 



1957, Oceanographic observations, 1956, 



east coast of the United States. U.S. 



Fish Wildl. Serv., Spec. Sci. Rep. Fish. 



233, 132 p. 

 DAY, C. GODFREY. 



1959a, Oceanographic observations, 1957, 



east coast of the United States. U.S. 



Fish Wildl. Serv., Spec. Sci. Rep. Fish. 



282, 123 p. 

 1959b. Oceanographic observations, 1958, 



east coast of the United States. U.S. 



Fish Wildl. Serv,, Spec. Sci. Rep, Fish. 



318, 119 p. 



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