Figure 7.Annual landings of the migratory population of Chi-
nese sturgeon,A. sinensis ,in the Yangtze River.
low the Gezhouba Dam since it closed in January
- Except in 1981, we found spawning activities
each year in the major spawning site. Because the
spawning population was overfished below the dam
in 1981 and 1982 (Figure 7), few fish were available
to spawn in 1982, and as a result, spawning activities
were scattered and abnormal. Table 7 shows that
spawning dates after the damming are similar to
those before the damming. In half of the years sam-
pled, spawning only occurred once at the major
spawning site, but in 1987 we found eggs in stomachs
of copperfish for 17 days, which we interpret as evi-
dence of two spawnings during this period. We are
not sure what factors trigger spawning, although
some researchers consider that water level (Anony-
mous 1988) or water temperature (Deng et al. 1991)
are critical factors. Buckley & Kynard (1985) re-
ported that shortnose sturgeonA. brevirostrumre-
quire a specific water velocity to spawn, and Chi-
nese sturgeon may be similar. We believe that the
available spawning sites are insufficient because
ripe females can still be taken even after the spawn-
ing period is over.Harvest and stock size of the migratory population
in the Yangtze River .-Before 1981, sturgeon fisher-
ies mainly occurred in the middle and upper reaches
of Yangtze. Fishing was unlimited, but seasonal,
and mostly in the fall. Gear include gill nets (upper
reach) and row hooks (middle reach). Catch data
are not available prior to 1972. Between 1972 and
1980, the annual mean catch of migratory adults was
517 individuals or 77 550 kg (150 kg per individual)
for the entire river. When the river was dammed in
January 1981, almost all of the fish trapped in a small
area below the dam were caught in 1981 and 1982.
As a consequence, the catch reached a peak of 1163,Table 7.Hydrological characteristics of spawning areas used byA. sinensisat Yichang below Gezhouba Dam from 1983-1993.
Water temperature (°C) Water level (m) Silt content (kg m-3) Water velocity (m s-1)2Date Days^1 Start Fluctuation Start Fluctuation Start Fluctuation Start Fluctuation7.11.83 5 17.9 17.9–17.2 43.01 42.90–43.55 0.35 0.35–0.43 0.89 0.88–1.07
16.10.84 7 18.9 18.9–18.6 45.00 45.45–44.36 0.66 0.33–0.66 1.42 1.30–1.4913.10.85 7 19.8 19.8–18.8 44.75 44.75–44.22 0.69 0.69–0.60 1.39 1.39–1.28
7.11.85 7 17.5 17.5–15.7 43.73 44.31–43.41 0.29 0.56–0.21 1.15 1.39–1.07
21.10.86 5 18.2 18.3–18.0 45.38 45.38–44.35 0.87 0.87–0.51 1.39 1.39–1.28
31.10.87 17 17.2 17.4–15.8 43.00 43.29–41.49 0.44 0.44–0.09 1.16 1.16–0.90
13.10.88 4 18.8 18.8–18.3 46.33 46.33–45.41 0.59 0.59–0.45 1.19 1.19–1.72
3.11.88 3 18.6 18.6–18.0 43.46 43.46–42.84 0.45 0.45–0.35 1.26 1.26–1.18
27.10.89 8 17.7 18.0–17.7 46.59 46.59–44.52 1.00 1.00–0.53 1.66 1.66–1.38
15.10.90 7 18.9 19.0–18.8 47.29 47.29–45.49 1.32 1.91–0.67 1.98 1.98–1.4913.11.84 5 17.1 17.1–16.8 41.71 41.69–41.90 0.10 0.10–0.08 0.81 0.80–0.8431.10.90 5 17.8 17.8–17.2 44.23 44.23–43.11 0.30 1.28–1.09 1.28 1.28–1.09
23.10.91 7 19.4 19.4–18.0 44.24 44.24–43.44 0.62 1.82–1.32 1.82 1.82–1.32
17.10.92 8 19.0 19.2–18.6 43.71 43.71–42.78 0.70 0.98–0.38 1.27 1.27–1.13
17.10.93 6 20.0 20.0–18.8 45.20 46.31–44.70 0.83 1.24–0.79 2.07 2.20–1.81
30.10.93 7 18.0 18.0–17.2 44.24 44.24–43.54 0.59 0.67–0.49 1.73 1.93–1.29(^1) Number of days during which sturgeon eggs were found in the stomach ofCoreius guichenoti.
(^2) Mean water velocity at the Moji monitoring section; other hydrological data provided by Yichang Hydrological Monitoring Station.