Rulifson and Batsavage: Population demographics of Alosa mediocris 
225 
Two separate methods were used to estimate length 
at age. FL at age was estimated from the von Berta- 
lanffy growth equation (Cailliet et al., 1986), which was 
calculated with mean back-calculated FL at age (sexes 
combined). Back calculations also were computed by 
the Dahl-Lea direct proportion method (DeVries and 
Frie, 1996) with the following equation: 
L[ = (S[ / S c ) L c , (1) 
where Lj = back-calculated FL( mm) of the fish at forma- 
tion of the i th increment; 
L c = FL (mm) at capture; 
S c = otolith radius at capture; and 
S; = otolith radius at the i th increment. 
Mortality estimates 
Mortality was estimated for ages where recruitment 
was more than 95% complete (on the basis of catch 
curves) — for males ages 3-5, females ages 4-6, and sex- 
es combined ages 3-6 to eliminate age classes not fully 
recruited to the spawning population. Total instanta- 
neous mortality ( Z ) was calculated by least-squares re- 
gression, and by estimating the slope of the line from 
the catch curve of a single season. Annual total mortal- 
ity (A) was estimated by taking the inverse natural log 
of -Z and subtracting the value from 1 (Ricker, 1975): 
A = 1 - e- z . (2) 
Spawning history 
Spawning history for both sexes was determined by 
counting the number of spawning marks on the scales; 
spawning marks are formed by erosion of the scale 
margin from lack of feeding during the spawning mi- 
gration (Cating, 1953; Pate, 1972). Spawning marks are 
thicker and more visible than the winter annuli that 
form before a fish matures sexually. The presence of 
these marks on scales is indicative of repeat spawners 
in a population, and the percentage of repeat spawn- 
ers can be calculated. The percentage of the population 
that was sexually mature was calculated by sex by di- 
viding the number of fish with developed gonads by the 
total number of fish examined. 
Fecundity and gonadosomatic index 
When this research was completed in 1996, gonad- 
al maturity and fecundity were not well understood. 
We understand now that the Hickory Shad is a batch 
spawner (Murauskas and Rulifson, 2011), a character- 
istic that requires special consideration in the estima- 
tion of fecundity (Olney et al., 2001; Murua and Sabo- 
rido-Rey, 2003). However, in 1996, sexual maturity was 
assigned by visual inspection of the gonads. We present 
the gonadosomatic index (GSI) here as documentation 
and for comparison with other limited studies of this 
species in other watersheds. For sexually mature indi- 
viduals, the number of ova present in each ovary was 
estimated by the gravimetric method. 
Each preserved whole ovary was blotted with a wet 
paper towel and then weighed to the nearest 0.01 g. 
Three subsamples of ovarian tissue, each -0.50 g, were 
taken from each ovary at the anterior, medial, and 
posterior regions. Each subsample was weighed, the 
ova were counted, and the number of ova per grain of 
ovarian tissue was calculated. The mean number of ova 
present in the 3 subsamples was multiplied by ovary 
weight to estimate the total number of ova in that 
ovary; the sum of the ova in the 2 ovaries was consid- 
ered the estimate of total potential fecundity. The GSI 
was estimated by dividing the gonad weight by somatic 
body weight (no gonads or gastrointestinal tract), and 
then multiplying the quotient by 100. The mean GSI 
was calculated by week so that temporal changes in 
the GSI could be identified. Two-sample t-tests with 
assumed unequal variances were used to detect dif- 
ferences between left and right ovaries in weight and 
total counts of ova. To detect significant differences in 
the number of ova per gram of ovarian tissue between 
the 3 regions of the ovary, analysis of variance was 
performed with Statistical Analysis System 16 software. 
Regression analysis was used to predict potential fe- 
cundity on the basis of FL, somatic weight, and age. 
Significance was assigned an alpha (a) value of 0.05. 
Mesentery fat and gut content analyses 
The few literature references available on this topic 
indicate that Hickory Shad usually do not feed dur- 
ing the spring spawning migration (White and Curtis 17 ; 
Curtis 18 ; Perkins and Dahlberg, 1971; Pate, 1972; Har- 
ris et al., 2007). However, we observed Hickory Shad in 
the Roanoke River (during this study) and Neuse River 
(Murauskas and Rulifson, 2011) with full stomachs, 
and Harris et al. (2007) found similar trends in the St. 
Johns River population. To determine whether feeding 
or fat reserves were more important during the phase 
of inland spawning migration, we removed mesentery 
fat from the viscera and weighed it to the nearest 0.01 
g. Food items removed from the stomach and intestine 
were identified to the lowest practical taxon, enumer- 
ated, and weighed to the nearest 0.01 g. T-tests were 
used to test for significant differences in mesentery fat 
between males and females and between fish collected 
in Albemarle Sound and fish collected in the Roanoke 
River. Relationships between mesentery fat and somat- 
16 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
1 'White, M. G., Ill, and T. A. Curtis. 1969. Anadromous fish 
survey of the Black River and Pee Dee River watersheds. 
Project AFS-2-4, 73 p. South Carolina Wildlife Resources 
Department, Charleston, SC. 
18 Curtis, T. A. 1970. Anadromous fish survey of the Ashley 
River watershed. Project AFS-2, 91 p. South Carolina Wild- 
life Resources Department, Charleston, SC. 
