82
objections to this view. However, those who had
supported the idea of a marine origin for the
fauna of Lake Tanganyika might have been
convinced about this. Nevertheless, the openwater fi sh fauna was dominated by small clupeids,
which are now called Tanganyika sardines.
The algae in the open water of Lake
Tanganyika provide an excellent illustration of
the difference between standing crop and production. Standing crop is the weight per unit area
measured in dry weight, or amount of carbon,
present at one particular time. Primary production is the amount of new living material, measured as carbon fi xed by photosynthesis per unit
of time. In Lake Tanganyika, the standing crop
was low while primary production was high.
Zooplankton in the open water are also generally
scanty. Diatoms are sometimes quite abundant.
Yield of fi sh is quite high in comparison to
primary production. The food chain could be
super-effi cient. Non-mixing of the lake could be
the reasons for less productivity.
6.4.2 Lake Baikal
It is the deepest and one of the biggest lakes in
the world. It ranks seventh in area amongst the
very big lakes in the world. Lake Baikal (55° N to
110° E, altitude 455 m, lake area 31,500 km
2 ,
catchment area 540,000 km
2 , volume 23,000 km
3 ,
max. depth 1,620 m, mean depth 740 m) is situated
in Siberia in Russia. Its volume is said to account
for one-fi fth of the world’s total reserves of freshwater. The lake is contained within a steep-sided
trough, 650 km long. Evidences from steep-sided
terraces revealed that the lake was perhaps deeper
than 1,620 m in the past. There is little shallow
water even at the edges of the lake. About 31 %
of the lake area is >250 m deep.
More than 300 rivers fl ow into Lake Baikal
but the prominent inlet is the Selenga River which
enters the lake at the southeastern boundary.
However, there is only one prominent outlet,
namely, the river Angara which comes out of the
lake from its southwestern boundary. Thus, there
is considerable risk of pollutants being brought
into the lake (by numerous inlets) with retention
of maximum amount and fl ushing out of less.
The volume of infl ows increases greatly when ice
and snow melt on mountain at the end of severe
winters. The lake freezes over as winter proceeds.
Ice cover lasts for about 4–5 months, depending
on the severity of winter. Winter is intensely cold
and dry.
c 35 % of fl ora and c 65 % of fauna of Lake
Baikal are endemic. Several of its freshwater
groups closely resemble marine forms. However,
>1,500 animal species have been described from
Lake Baikal. Of these, 80 % of the pelagic dwellers
are endemic. They comprise >87 % endemic
genera and at least 11 endemic families or subfamilies. The FW shrimps are one of the most
spectacular examples of a group evolving in an
isolated place to form species found no where
else. There are c 255 species of fi shes in Lake
Baikal grouped into 35 genera, 34 of which are
endemic. They range from pike ( Esox lucius )
and perch ( Perca fl uviatilis ) to the family
Comephoridae which contains one or two endemic
species, namely, Comephorus , C. baicalensis and
C. dybowskii. They, generally, live at a depth of
500 m. Signifi cantly, sea omul ( Coregonus
autumnalis migratorius ) forms signifi cant component of commercial fi sh catch from Lake
Baikal. Further, as in the case of cichlid fi sh of
Lake Victoria, in Lake Baikal also, there seems to
be a good deal of overlap between species
adapted to similar conditions. Further, many
groups have evolved numerous species which
occur no where else in the world. The Baikal seal
( Pusa or Phoca sibirica ) is found only in Lake
Baikal. It is closely related to another seal which
lives isolated in the Caspian Sea.
It is supposed that the greatest assortment of
endemic species in Lake Baikal has evolved in
the deep water of the lake. It is believed that the
diversity of habitats encourage the evolution of
species. It could be, further, assumed that almost
constant condition prevailed in the deep water
region of Lake Baikal for millions of years. In
addition to above, the diatoms are also represented by about 310 endemic and 369 nonendemic species. However, amphibians have not
been reported. Also, there are not many insects
except 7 species of caddis fl y. The River Selenga
6 Lakes of the World
objections to this view. However, those who had
supported the idea of a marine origin for the
fauna of Lake Tanganyika might have been
convinced about this. Nevertheless, the openwater fi sh fauna was dominated by small clupeids,
which are now called Tanganyika sardines.
The algae in the open water of Lake
Tanganyika provide an excellent illustration of
the difference between standing crop and production. Standing crop is the weight per unit area
measured in dry weight, or amount of carbon,
present at one particular time. Primary production is the amount of new living material, measured as carbon fi xed by photosynthesis per unit
of time. In Lake Tanganyika, the standing crop
was low while primary production was high.
Zooplankton in the open water are also generally
scanty. Diatoms are sometimes quite abundant.
Yield of fi sh is quite high in comparison to
primary production. The food chain could be
super-effi cient. Non-mixing of the lake could be
the reasons for less productivity.
6.4.2 Lake Baikal
It is the deepest and one of the biggest lakes in
the world. It ranks seventh in area amongst the
very big lakes in the world. Lake Baikal (55° N to
110° E, altitude 455 m, lake area 31,500 km
2 ,
catchment area 540,000 km
2 , volume 23,000 km
3 ,
max. depth 1,620 m, mean depth 740 m) is situated
in Siberia in Russia. Its volume is said to account
for one-fi fth of the world’s total reserves of freshwater. The lake is contained within a steep-sided
trough, 650 km long. Evidences from steep-sided
terraces revealed that the lake was perhaps deeper
than 1,620 m in the past. There is little shallow
water even at the edges of the lake. About 31 %
of the lake area is >250 m deep.
More than 300 rivers fl ow into Lake Baikal
but the prominent inlet is the Selenga River which
enters the lake at the southeastern boundary.
However, there is only one prominent outlet,
namely, the river Angara which comes out of the
lake from its southwestern boundary. Thus, there
is considerable risk of pollutants being brought
into the lake (by numerous inlets) with retention
of maximum amount and fl ushing out of less.
The volume of infl ows increases greatly when ice
and snow melt on mountain at the end of severe
winters. The lake freezes over as winter proceeds.
Ice cover lasts for about 4–5 months, depending
on the severity of winter. Winter is intensely cold
and dry.
c 35 % of fl ora and c 65 % of fauna of Lake
Baikal are endemic. Several of its freshwater
groups closely resemble marine forms. However,
>1,500 animal species have been described from
Lake Baikal. Of these, 80 % of the pelagic dwellers
are endemic. They comprise >87 % endemic
genera and at least 11 endemic families or subfamilies. The FW shrimps are one of the most
spectacular examples of a group evolving in an
isolated place to form species found no where
else. There are c 255 species of fi shes in Lake
Baikal grouped into 35 genera, 34 of which are
endemic. They range from pike ( Esox lucius )
and perch ( Perca fl uviatilis ) to the family
Comephoridae which contains one or two endemic
species, namely, Comephorus , C. baicalensis and
C. dybowskii. They, generally, live at a depth of
500 m. Signifi cantly, sea omul ( Coregonus
autumnalis migratorius ) forms signifi cant component of commercial fi sh catch from Lake
Baikal. Further, as in the case of cichlid fi sh of
Lake Victoria, in Lake Baikal also, there seems to
be a good deal of overlap between species
adapted to similar conditions. Further, many
groups have evolved numerous species which
occur no where else in the world. The Baikal seal
( Pusa or Phoca sibirica ) is found only in Lake
Baikal. It is closely related to another seal which
lives isolated in the Caspian Sea.
It is supposed that the greatest assortment of
endemic species in Lake Baikal has evolved in
the deep water of the lake. It is believed that the
diversity of habitats encourage the evolution of
species. It could be, further, assumed that almost
constant condition prevailed in the deep water
region of Lake Baikal for millions of years. In
addition to above, the diatoms are also represented by about 310 endemic and 369 nonendemic species. However, amphibians have not
been reported. Also, there are not many insects
except 7 species of caddis fl y. The River Selenga
6 Lakes of the World