AGE OF ATLANTIC SHAD FROM SCALES 



199 



one wishing to learn to read shad scales accurately 

 can do so in a relatively short time. It is sug- 

 gested that anyone interested in applying these 

 criteria should select several hundred shad scales, 

 and read them a number of times until the differ- 

 ent readings reach a desired level of agreement. 



SUMMARY 



From scales of the Atlantic shad (Alosa scupi- 

 ilisx'una) collected in the Hudson River in the 

 spring of 1950, 164 of the more easily read scales 

 were selected to serve as the basis for establishing 

 criteria for determining the age of shad from their 

 scales. 



By counting the number of transverse grooves 

 entering the fresh- water zone, and the first, second, 

 and third annuli, it was found that the number of 

 such grooves is relal i vely constant from fish to fish. 

 The predominant number of transverse grooves 

 entering the fresh-water zone was 3; the first 

 a min lus. ."> ; the second annulus, 1": and the third 

 anuulus. 14. En a period of slow growth when two 

 annuli lay close together, the distance between the 

 transverse grooves was found to he proportionately 

 less. Once the location id' an annulus was deter- 

 mined by groove count, the annulus usually could 

 he t raced. 



When a .shad has previously spawned the spa wil- 

 ing marks must lie used with the annuli to deter- 

 mine the a^e <d' the fish. The spawning marks are 

 scarlike rings extending around the anterior por- 

 tion of the scale which are caused by erosion or 

 absorption of the scale when I he shad enters fresh 

 water to spawn. The amount of absorption that 

 occurs depends on the age of the tisli at the time it 

 makes its first spawning migration. Thus, it was 

 found that scale absorption on a fish making its 

 first spawning migration when :'. years old usually 

 extends from one-fourth to one-half the distance 

 to the second annulus. On a scale from a 6-year- 



old shad spawning for the first time, however, the 

 absorption usually extends to or over the fifth 

 annulus. It is important, therefore, to examine 

 scales closely from fish apparently spawning for 

 the first time at ."> or 6 years of age to determine if 

 an annulus has been absorbed during the first 

 spawning migration. Usually, remnants of the 

 annulus previous to the first spawning can be seen 

 near the edge of the posterior region of the scale. 

 When there are several spawning marks on a scale, 

 and the marks have overlapped each other, traces 

 of each spawning mark are clearly seen just pos- 

 terior io the baseline. 



LITERATURE CITED 



Borodin, V a. 



1925. Age of shad (Alosa sapidissima Wilson) as de- 

 termined by i lie scales Report of investigations con- 



reriiini; shad in I he rivers nf Connecticut, part II. pp. 



46 51. Connecticut State Board of Fisheries and 

 Came. Hartford. 



Gbi iiii. .Inn \ R. 



1937. Biological survey of the inner Hudson water- 

 shed. II. Fishes of the area with annotated list. 

 Biological survey (1936), No. XI, pp. 45-103, New 

 \ ik Conservation Department. Supplemental to 

 26th annual report, 1936. 



Ham mm:. I! \i PH Cri:i lis 



1942. The boming instinct of the Chesapeake shad, 

 ilosa sapidissima Wilson, as revealed by a study of 



their scales. Thesis, University of Maryland (type 



\\ liltell I . 



l.i t\i. A. II. 



1925. 'the life-history of the shad i Ylosa sapidissima 

 i Wilson i i with special reference to the factors limit- 

 ing its abundance. Contributions in Canadian Biol 

 ogy, vol. -. part I. No. 11, pp. Hit 284. University 

 of Toronto Press, Toronto, Canada. December 1, 



ltlL'4. 

 Mess. DOl 'I IS I>. 



pin; Preliminary studies of the shad I Uosa sapidis- 

 sima) catch in tlie Lower Connecticut River, 1944. 

 Trans. Eleventh North American Wildlife Conf., pp. 

 230-30. American Wildlife Institute. Washington, 

 D.C. 



O 



