FISHERY BULLETIN: VOL. 73, NO. 3 



twice weekly in later years. Sampling occurred 

 from 5 April to 19 May in 1963, from 20 March to 18 

 May in 1964 and from 26 March to 7 May in 1965. In 

 1964 and 1965, at least, several collections were 

 made both before and after the first and last 

 American shad were captured, but a few fish were 

 captured on the first and last sampling dates in 

 1963. My sampling in 1963 essentially ended when 

 the run did at Lambertville. I captured 1 fish after 

 15 May, and the Lewis Fishery captured 5 fish 

 after that date of a total catch of about 4,000 fish 

 (Chittenden 1969). The number of seine hauls and 

 time of sampling varied each day during 1963. 

 After 1963 two seine hauls were made from 1100 

 to 1300 EST on each sampling day after the first 

 American shad was landed. In spring 1965, low 

 dissolved oxygen levels near Philadelphia blocked 

 upstream passage of part of the spawning run, 

 and few fish were captured at Lambertville (Chit- 

 tenden 1%9). Hundreds of dead fish were collected 

 during a fishkill seaward of Philadelphia in the 

 area from Paulsboro, N.J., to Marcus Hook, Pa., 

 during the period from 21 May to 10 June. Sex and 

 size composition data for 1961 and 1962 were ob- 

 tained from cooperative surveys (hereinafter 

 referred to as the Tri-state Surveys) using 

 rotenone during July and August by the states of 

 New Jersey, New York, and Pennsylvania in con- 

 junction with the U.S. Fish and Wildlife Service. I 

 personally examined many of the American shad 

 collected. 



Each fish collected after 1962 was measured and 

 was sexed by examination of the gonads, and 

 scales were taken from the midline of the left side 

 below the dorsal fin following Cating (1953) or 

 from the same area on the right side. Many fish 

 collected near Marcus Hook during 1965 had lost 

 all or nearly all their scales, so scales were taken 

 where available on these fish. Scales selected for 

 age determination were cleaned and were dry- 

 mounted between glass slides. Aging was done 

 with a microprojector using Cating's (1953) 

 method which was verified by La Pointe (1958) and- 

 Judy (1961). Scales were examined in the time 

 sequence 1963, 1964, and 1965 for an initial deter- 

 mination. Many of the large fish were known to 

 have been misaged when the sequence was 

 completed. Scales were next thoroughly mixed to 

 remove bias due to knowledge of the collection 

 year and were reread. The first two readings 

 disagreed on 31 of 301 fish (10%) from 1963, 38 of 

 199 (19%) from 1964, and 3 of 184 (2%) from 1965. 

 Of these, 32 disagreements were on females reas- 



signed from age-group V to VI (9 from 1963 and 23 

 from 1964). A third examination of the misaged 

 scales agreed with the second on 67 of the 72 fish. 

 The remaining 5 were discarded. 



RESULTS AND DISCUSSION 

 Sex Composition of the Spawning Runs 



Many American shad were captured at Lam- 

 bertville during 1963 (301 fish) and 1964 (199 fish). 

 Figure 1 shows trends in the cumulative percent- 

 age of males as these spawning runs progressed. 

 Trends were similar during each year although the 

 1963 run contained a much higher percentage of 

 males than the 1964 run. The cumulative propor- 

 tion of males decreased as the run progressed in 

 agreement with the observations or statements of 

 many workers including Stevenson (1899), Prince 

 (1907), Leach (1925), Hildebrand and Schroeder 

 (1928), Nichols and Tagatz (1960), and Walburg 

 and Nichols (1967). 



Annual sex compositions of the runs from 1961 

 to 1965 are presented in Table 1 with 95% con- 

 fidence limits for the proportion of males based 

 upon normal approximations except for 1962 when 

 a Poisson approximation to the binomial was used 

 (Cochran 1953). Annual sex composition varied 

 greatly from 1961 to 1965. It was male dominated 

 from 1961 to 1963 and female dominated 

 thereafter. 



> 60 



(7) 



Figure 1. -Trends in the cumulative percentage of male 

 American shad. Numbers in parentheses represent cumulative 

 numbers of fish captured. 



488 



