162 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Florida and as late as June in Canada. The young 

 remain in the rivers until fall, attaining lengths 

 from 3 to 5 inches, then migrate to sea. Winters 

 are probably spent off the Middle Atlantic, and 

 summer and fall in the Gulf of Maine. After 

 reaching maturity, in 3 to 6 yeai*s, they return to 

 the rivers to spawn. Adult shad native to streams 

 north of Cape Hatteras (N.C.) that survive 

 spawning and other hazards return to the sea and 

 re-enter the rivers to spawn again in successive 

 years. Shad native to streams south of Cape 

 Hatteras die after spawning (Talbot and Sykes, 

 1958). 



MATERIALS AND METHODS 



In the fall of 1952, 100,000 downstream migrant 

 juvenile shad were marked on the Connecticut 

 Eiver in the Windsor Locks Canal, Windsor Locks, 

 Conn. Marking of these fish, which averaged 

 about i inches in fork length, was accomplished 

 by clipping the right pelvic fin close to the body 

 of the fish. Juveniles were trapped, seined, and 

 marked in one level of the canal and then placed 

 in a lower level of the canal and flushed into the 

 main river. Samples of fish were held overnight 

 to obtain an estimate of mortality. Mortality 

 from marking was estimated at 30 percent ; there- 

 fore, it was assumed that 70,000 marked juveniles 

 were returned to the river. 



The first marked fish were recaptured in the 

 Connecticut River in 1956 from commercial catches 

 and shad passed by the fishway at Hadley Falls 

 Dam, Holyoke, Mass. Subsequent recoveries were 

 made in 1957 and 1958 from commercial and sport 

 catches. Approximately 35,000 shad were ex- 

 amined annually. Fi-om the 1956 collection it was 

 determined that some shad had malformed, or nat- 

 urally missing, pelvic fins. Therefore, in 1957, 

 fish with various pelvic fin abnormalities were 

 collected so that a wide assortment of abnormal 

 fins would be available for comparison with 

 marked fins. The pelvic girdle section of each 

 fish collected was removed, labeled, and preserved. 

 In addition, scale samples were taken and the 

 length, weight, and sex recorded. 



EXAMINATION OF SCALES 



Two scales from each fish collected were im- 

 pressed in plastic, using a modification of the 

 method described by Greenbank and O'Donnell 



(1950). The scale impressions were read on an 

 Eberbach projector, by two biologists using Cat- 

 ing's (1953) method for determining age of shad. 

 Age readings were compared and the results 

 confirmed. 



In this method the scale edge is counted as a year 

 mark because the last annulus (near scale periph- 

 ery) is frequently eroded during the spawning mi- 

 gration. For example, a shad spawning for the 

 first time (virgin fish) at 4 years of age has 3 annuli 

 on the scale plus the scale edge for a total age of 

 4 years. After shad spawn and return to the sea, 

 renewed feeding and resumption of growth leaves 

 a characteristic scarlike mark on the scale edge 

 where erosion occurred during the spawning mi- 

 gration (Moss, 1946). This is designated as a 

 spawning mark and is used in place of the eroded 

 annulus, formed prior to spawning, for determin- 

 ing age of "repeater" fish (those spawning for 

 the second or more times) . For example, a 6-year- 

 old rejieater spawning for tlie second time has 4 

 annuli and 1 spawning mark which, when read to 

 include the scale edge, gives a total age of 6 years. 

 The 4 annuli and 1 spawning mark indicate that 

 this fish first spawned at 5 years of age and was on 

 its second spawning run when captured. 



EXAMINATION OF PELVIC FINS 



Examination of the pelvic fin sections indicated 

 that they contained malformed, missing, and 

 marked fins. Malformed and missing fins are 

 often fomid in fish as evidenced from studies by 

 Cable (1956), Code (1950), and Rich and Holmes 

 (1928). Marked fins were characterized by a 

 varied pattern of fin regeneration ranging from no 

 regeneration beyond formation of scar tissue to 

 almost complete, but distorted regeneration. 

 These findings are not unusual since, as reported 

 by Stuart (1958), fin clipping seldom results in a 

 uniform series of marks. From microscopic 

 examination of regenerated marked fins, Stuart 

 found that new gi-owth of fin rays does not extend 

 in a regular manner but commences as a thickened 

 and undifferentiated cap, the comiective and other 

 tissues keeping pace with the gi'owth of the adja- 

 cent rays. The degi'ee and nature of fin regenera- 

 tion was usually dependent on the angle of the cut 

 and the amount of dermal-fin-ray tissue removed 

 during clipping. 



The pelvic fin section of each shad collected in 



