determine the age at first reproduction for the en-
tire subsample of 341. The ages of individuals which
belong to the class of initial spawners are not signif-
icantly different from the age of first spawning for
repeated spawners (t=0.485 < t0.005= 2.358). This
demonstrates the validity of our determination of
initial reproductive marks. It also suggests that the
average age at initial reproduction ofA. sinensisis
14.3 years. Because of the blurring of structures fol-
lowing the initial spawning mark, and of insufficient
sample, we cannot verify the time intervals between
repeated spawning migrations.
Chinese sturgeon exhibit different individual
growth rates. Commonly, females are larger than
males of the same age. For instance, 14 year old
males had a mean TL of 248.0 cm (N=35, SD=
13.00, range 221-274 cm) whereas females had a
mean TL of 289.6 cm (N = 7, SD = 11.76, range 272-
306).Byage 18 years, males had a mean TL of 256.9
cm (N=15, SD=l4.85, range 234–285 cm) and fe-
males had a mean TL of 300.4 cm (N=11, SD=26.00,
range 263–340 cm). The growth rate ofA. sinensisis
one of the highest known among the species of Aci-
penderifomes (Hol
^
cík 1989, Smith 1985).Some changes in age conmposition in recent years. –
We were interested in examining age composition
of the population as it may have changed since com-
pletion of the Gezhouba Dam in 1981. With very
limited samples available. we classified them into
four groups: group I (1981–1983), group II (1984–
1986), group III (1987–1989) and group IV (1990–
1993) (in I990 only 3 specimens were available).
ANOVA shows that the differences in age are notsignificant between each group for females and also
for males before 1990. Males in group IV, however,
are significantly older than those in groups I, II and
III (p < 0.01). The mean age of group IV males is 17.1
years while those of group I, II and III are 13.0, 12.8
and 12.6 years, respectively. Furthermore, males
younger than 12 years are very underrepresented
(percentages younger than 13 years were 47.1%,
47.5%, 43.5% and 4.7% in groups I to IV, respec-
tively). No fish born in 1982 and 1983 were found,
and only two fish born in 1981 and 1984 were found.
On the other hand, the number of repeated spawn-
ers was higher for group IV males (26.2, 28.6, 34.4
and 46.5% ingroup I, II, III and IV, respectively)
but did not increase for females (52.0, 69.2, 65.0 and
42.6% in group I, II, III and IV, respectively). Taken
together, these results suggest that recruitment of
males to the population is declining at a dangerous
rate.Gonadosomatic index anditsalteration after con-
struction of Gezhouba Dam.-As mentioned above,
two groups of spawning adults can be found in the
river at the same time, one with gonads at stage III
(or rarely II) and another with gonads at stageIVor
V (or rarely VI). Before completion of the Gezhou-
ba Dam, females stage III gonads exhibited these
characteristics; gonadas fat 60–70% (September
and October) or 20–60% (November and Decem-
ber); GSI 2.8–7.1% (mean 4.8%, September and
October) or 2.4–9.0% (mean 7.3%. November and
December); and egg diameter 2.0–2.5 mm (Septem-
ber and October) or 2.5–3.5 mm (November and
December; summarized from Y.Z.Leng in Anony-T able 5. Ages of Acipenser sinensis and repeated reproduction (1981-1993).
(^1) As explained in text, this estimate compiles data from the first column in the table together with data from analysis of spawning marks
detectcd in fish that made a subsequent spawning migration. N = number of samples, x = mean age, SD = standard deviation.