CHITTENDEN: DYNAMICS OF AMERICAN SHAD RUNS 



Table 1.- Annual sex compositions of American shad runs, 

 1961-65. 



Year 



Sample size 



Proportion 

 male (p) 



95% CL about pi 



'Confidence limit for proportion of males. 



Size Composition 



Mean fork lengths, numbers of fish, 95% con- 

 fidence limits for means, and 99% limits for in- 

 dividuals collected at Lambertville or the tidal 

 area and during the Tri-state Surveys are sum- 

 marized in Table 2. Data were originally expressed 

 in total or fork length depending on year of 

 collection. Means and confidence limits were 

 transformed to fork lengths in inches using the 

 regression of fork on total length presented by 

 Chittenden (1969) and were then transformed to 

 metric units. Females from Marcus Hook and 

 Lambertville did not appear significantly 

 different in size and were pooled. Males from 

 Marcus Hook were significantly smaller {t = 4.67) 

 than those from Lambertville, and they were not 

 combined. 



Fish were smaller in 1961 and 1962 than in later 

 years, and this probably reflects the presence of 

 very young individuals of the strong 1958 and 1959 

 year classes (see section "Comparative Year-Class 

 Strengths"). Females averaged about 50 mm (2 

 inches) longer than males each year. Confidence 



limits for individuals indicate that there were few 

 females longer than 545 mm (21.5 inches) and few 

 males longer than 505 mm (19.9 inches). Maximum 

 observed sizes were 559 and 495 mm (22.0 and 19.5 

 inches) for females and males, respectively. Small 

 fish did not migrate upstream. The smallest 

 female was about 64 mm (2.5 inches) longer than 

 the smallest male each year. There were few 

 females shorter than 416 mm (16.4 inches) in 1963, 

 1964, and 1965, the smallest being 406 mm (16.0 

 inches). The smallest female observed was 376 mm 

 (14.8 inches) and 391 mm (15.4 inches) in 1961 and 

 1962, respectively. Confidence limits indicate that 

 there were few males shorter than about 337 mm 

 (13.2 inches) from 1962 to 1965. There were few 

 males shorter than 289 mm (11.4 inches) in 1961, 

 the smallest fish measured being 269 mm (10.6 

 inches). 



Age and Repeat Spawner Comsposition 



There were only 2.6% repeat spawners in 729 fish 

 examined from 1963 to 1965. Annual occurrences 

 were 1 of 299 fish (0.3%) in 1963, 3 of 199 (1.5%) in 

 1964, and 15 of 231 (6.5%) in 1965. Confidence limits 

 for the annual percentages are 0.0 to 1.9% (1963) 

 and 0.03 to 4.4% (1964) based upon Poisson 

 approximations and 3.5 to 9.5% (1965) based upon 

 the normal approximation. 



Table 3 summarizes male and female age-class 

 structures of the 1963 and 1964 runs at Lambert- 

 ville, pooled data for 1965 from Lambertville and 

 Marcus Hook, and data pooled over all years. 

 Fluctuations in age composition due to variable 

 year-class recruitment are apparent, but certain 

 general features of the age composition stand out. 



Table 2. -Summary of fork lengths of American shad, 1961-65. Lengths are in millimeters (top rows) and inches 



(bottom rows). 



'Confidence limit for mean fork lengtfi. 

 ^Confidence limit for indivdual fish collected. 



489 



