!• ISHKK Y BULLhTlN: VOL. 73, NO. 3 



Table 3.-Age-class structures of American shad, 1963-65. 



The following comments essentially apply to vir- 

 gin fish because the percentage of repeat 

 spawners was negligible. 



Age I and II males did not migrate upstream, 

 although one age II male was captured in 1964. 

 Few age III males migrated upstream, the per- 

 centage based on pooled data over all years being 

 less than 3%. Males migrated upstream primarily 

 at age IV (76%), but age V (20%) was also impor- 

 tant. Few males survived to age VI, and all were 

 virgin. No males older than age VI were captured. 

 No females younger than age IV or older than age 

 VII were observed. Only two age VII females (less 

 than 1% of the pooled total) were captured, and one 

 of these was a virgin. Females were primarily age 

 V (62%) when they first entered the fishery, but 

 ages IV (14%) and VI (24%) were also important. 



Comparative Magnitudes of 

 American Shad Runs, 1961-68 



I here define magnitude of American shad runs 

 as the numbers of adults reaching Lambertville on 

 their upstream migration. The magnitude of runs 

 as defined is influenced by year-class strength as 

 later defined herein and by dissolved oxygen levels 

 that the adults encounter during migration up- 

 stream past the Philadelphia area (Chittenden 

 1969). Chittenden examined in detail the annual 

 effects of oxygen upon passage of adults and 

 young. In general, dissolved oxygen is sufficiently 

 high that the earlier stages, at least, of the adult 

 run successfully migrate upstream. 



Reasonably precise estimates of the compara- 

 tive magnitudes of American shad runs in the 

 1960's are available from three sources of evidence: 

 1) catches of the Lewis Fishery at Lambertville 

 presented by Chittenden (1974), 2) my own catches 

 at Lambertville, and 3) sex compositions of the 

 runs presented in Table 1. 



Lewis Fishery annual catch /seine haul records 

 indicate the comparative magnitudes of runs in 

 descending size order were: 1963 (56.1 fish), 1964 

 (18.3), 1962 (13.9), 1965 (6.6), 1967 (3.7) = 1961 (3.5), 

 and 1966 (1.8) = 1968 (1.2). Values in parentheses 

 represent catch/seine haul. My annual catch/seine 

 haul at Lambertville for the time period between 

 capture of the first and last fish was 17.4 fish in 

 1963, 9.0 in 1964, and 3.0 in 1965, a pattern in 

 agreement with the Lewis Fishery records. My 

 general impressions derived from angling 

 experience, interviews with other anglers, and 

 visual observations of the abundance of adult 

 American shad during extensive float trips each 

 year from 1961 to 1974 are in general agreement 

 with the patterns suggested by the Lewis Fishery 

 records. Runs were much smaller from 1966 to 1968 

 than from 1962 to 1964. The size of the run in 1965 

 (and possibly 1961 based on my general impres- 

 sions) was intermediate between the sizes in these 

 two periods. 



The relative magnitudes of runs estimated from 

 sex composition data (Table 1) agree with patterns 

 indicated by catch records at Lambertville. The 

 sex ratio shift from 1963 to 1964 suggests passage 

 through the fishery of a year class stronger than 

 the one immediately following because males tend 

 to enter the run a year earlier than females. This 

 indicates the 1963 run was larger than that in 1964. 



The male proportion at Lambertville in 1965 

 (0.52) is biased towards the high side because the 

 later part of the run was blocked by low dissolved 

 oxygen near Philadelphia. The male run was much 

 greater in 1963 than in 1964. Confidence limits for 

 the male proportion of fish collected at Marcus 

 Hook in 1965 were much lower than any single 

 daily male proportion in 1963 (Figure 1) but were 

 similar to the lowest daily male proportion in 1964. 

 Therefore, the 1965 run was probably similar in 

 sex composition to that of 1964. Females enter the 

 run a year older than males. Unless females suffer 

 a much lower annual mortality, similarity of sex 

 compositions suggests that the 1965 run was 

 smaller than the 1964 run-even before the fish 

 reached the Philadelphia area. The high female 

 proportion in 1965 suggests an even smaller run 

 was due in 1966, another year when low oxygen 

 levels blocked part of the run (Chittenden 1969). 

 Dissolved oxygen was suflSciently high throughout 

 the 1967 run to permit large numbers of fish to 

 reach Lambertville (Chittenden 1969). The Lewis 

 Fishery in 1967 did not make large catches to 

 reflect 1968 males or females associated with the 



490 



