VALIDITY OF AGE DETERMINATION FROM SCALES OF 

 MARKED AMERICAN SHAD 



By Mayo H. Judy, Fishery Research Biolosist, 

 Bureau of Commercial Fisheries 



In 1950, tlie U.S. Fish and Wildlife Service, as 

 the primary research agency of the Atlantic States 

 Marine Fisheries Commission, began a study of 

 the American shad (Alosa sapidissinut) on the At- 

 lantic coast of the United States. Objectives of 

 this investigation were to determine the causes for 

 decline in the commercial yield from approx- 

 imately 50 million pounds in 1896 to 8 million 

 pounds in 1950, to detennine conditions favoring 

 recovery, and to provide information for scientific 

 management of the fishery. A necessity for ac- 

 complisliing these objectives was an accurate 

 method of aging shad. 



Prior to this investigation, techniques for aging 

 shad had been presented by various workers. 

 Leim (1924) determined age by means of winter 

 rings or annuli on scales and established the rela- 

 tion between scale and body length. Borodin 

 (1925) presented a method of reading scales by 

 counting the number of transverse grooves and 

 dividing by 2 to determine the age in years. Bar- 

 ney (1925) found evidence in otolith markings to 

 indicate that age estimates as reported by Borodin 

 were correct, but Greeley (1937) stated that Boro- 

 din's method gave misleading results. Greeley 

 found that Leim's method of age determination 

 agreed with the results of his studies on Hudson 

 River shad. 



Gating (1953) proposed a method for reading 

 shad scales for total age, age at first spawning, 

 and number of times the fish had previously 

 spawned. Transveree groove counts were used to 

 .separate true from fasle annuli to the fourth an- 

 nulus, and age of fish spawing for the first time 

 was determined by counting the number of an- 

 nuli and adding 1 year for the scale edge. Age 

 of fish spawning for the second or more times was 



Ndte— Approved for publication December 5, 19B0. Fishery 

 Bulletin 18.0. 



590374 — «1 



obtained by counting the number of annuli plus 

 the number of spawning marks and adding 1 year 

 for ihe scale edge. 



Although Gating aged shad with apparent confi- 

 dence he did not establish the validity of his read- 

 ings. LaPointe (1958), using Gating's method, 

 validated the annulus to be a true year mark on 

 scales of fish spawning for the first time. He 

 found that Leim mistook the fresh- water mark for 

 the first annulus, thus causing a difference of 1 year 

 between Leim's age determination and those in his 

 study. Hammer (1942) confirmed that the fresh- 

 water zone was a distinct and measurable scale 

 growth formed while juveniles are in fresh water. 



In 1952, prior to the completion of Gating's 

 scale study, a marking program was conducted on 

 juvenile shad in the Gonnecticut River. The ob- 

 jective of this program was to recover in future 

 years marked fish of known age, thereby to check 

 the method employed by Gating and to establish 

 a correct method for aging shad from their scales. 

 This was deemed necessary because techniques 

 used prior to this time were subject to question. 



Data presented in this paper were derived from 

 the scales of marked adult shad recovered 4, 5, and 

 6 years following the marking program. Scales 

 from these fish of kno^^^l age were studied to de- 

 termine the validity of annuli and spawning 

 marks for age determination. 



Appreciation is expressed to the Gonnecticut 

 Power and Light Gonipany for use of the Windsor 

 Tiocks Canal System, and to the sliad fishermen 

 and fish dealers of the Connecticut River for their 

 cooperation in this study. 



LIFE HISTORY 



Shad range on the Atlantic coast from the St. 

 Johns River in Florida to tlie St. Lawrence River 

 in Canada. It is an anadiomous fish and spawn- 

 ing migrations begin as early as November in 



161 



