Amur extends down to the city of Blagoveshchensk
(upper Amur, 883 km); the middle reach continues
down to the mouth of the Ussuri River, opposite the
city of Khabarovsk (middle Amur, 975 km); and the
lower reach continues down to the estuary (lower
Amur, 966 km).Its hydrology is characterized by
spring floods. The difference between the highest
and lowest (winter) water levels is different in vari-
ous parts of the river: about 10 m in the upper Amur,
11 m in the middle Amur, 7–8 m in the lower Amur,
and up to 3m near the estuary. The current velocity
ranges from 0.5 to 2.0m sec–1. During the Quater-
nary, there were times when the Amur River bed
was either elongated 1.5–2.0 times, or when sea wa-
ter penetrated deeply into the continent, reaching
the area of Khabarovsk. Therefore, a seawater
body with a different gradient of salinity existed at
the location of the contemporary lower Amur and
estuary. These environmental changes evidently af-
fected sturgeon populations during their history in
this region (Svirskii 1968).
coastal brackish waters of the Sea of Okhotsk and
Sea of Japan, the second lives in the lower Amur,
the third in th middle Amur, and the fourth in the
lower reaches of the Zeya and Bureya rivers. We
know more about the estuary population than we
do about the other three, and most of our observa-
tions in this paper concern this group. Two ecolog-
ical morphs exist in the estuary population, which
we term the freshwater and brackish water forms
(Lukyanenko et al. 1979, Krykhtin 1985). The fresh-
water morph predominates, making up 75–80% of
the estuary population. They feed only in fresh wa-
ter. The brackish water form spends winter in the
river or estuary and, in late June-early July, mi-
grates downstream to the brackish water of the es-
tuary and northern part of the Tatar Strait, as well as
to the southwestern part of the Sakhalin gulf, to sa-
linities of12–16‰.
In autumn, when the salinity of the estuary in-
creases, brackish water kaluga return to the river,
where they overwinter together with freshwater ka-
luga. If storms rapidly fill the estuary with cold sea
water from the Sea of Okhotsk in late November-
early December, then some of the brackish water
individuals, mostly juveniles, cannot reach the fresh
water zones and die in the sea water at salinities of
about 29–30‰ and water temperatures below 0°C
(Krykhtin 1984a).
Kaluga consume mostly invertebrates in the first
year of life, later switching to juveniles of pelagic
fishes such as chum salmon,Oncorhynchusketa.At
age three to four years, kaluga start to feed on adult
fishes. In estuaries and coastal sea regions kaluga
catch saffron cod, Eleginus gracilis, and ocean
perch,Sebastes alutus.Cannibalism is frequent. Ka-
luga do not feed during winter nor do broodstock
eat during spawning migrations (Soldatov 1915,
Yukhimenko 1963, Svirskii 1971, Krykhtin 1979,
Krykhtin & Gorbach 1986).Kaluga sturgeonBiology and population structureKaluga is the largest freshwater fish in the Amur
River basin, reaching more than 5.6m in length,
more than 1000 kg in weight, and an age of more
than 80 years (Figure 2a,c). It inhabits the Amur
River Basin from the estuary to its upper reaches,
including several large tributaries and lakes (Nikol-
skii 1956). Young kaluga have been caught at the sea
during summer in coastal waters of the Sea of Ok-
hotsk (Kostarev & Tyurnin 1970, near the north-
eastern part of Sakhalin Island (Gritsenko & Kosty-
unin 1979), in the northern part of the Tatar Strait
(Krykhtin 1984a,b), and in the Sea of Japan near the
islands of Hokkaido (Amaoka & Nakaya 1975) and
Honshu(Honma& Itano1994). During the last
decade, the number of young fish increased consid-
erably in coastal waters of the northern part of the
Tatar Strait and in the southwestern part of the Gulf
of Sakhalin.
We recognize four populations of kaluga in the
Amur River basin. The first lives in the estuary andMaturation, spawning migration, and breedingMales from the estuary population spawn for the
first time at age 14–21 years, and females, at age 17–- Water temperature affects the time of matura-
tion of females: during warm years, females of the