94
by fi ve times that of the Lake District lakes.
Studies have been done on eight such lakes situated in two groups of four, just 4 km apart in the
valley of the River Blackwater which is a tributary of the Thames. The results show wide variations amongst the lakes in spite of their
proximity and similarity in size and age. In particular, differences have been revealed in the
amount of aquatic macrophytes (AM) found in
each lake. The emergent AM occur around the
shore wherever there is a shallow littoral zone.
However, the extent of their development
depends upon the shape of the lake basin and the
amount of shallow water. The variations in the
submerged and fl oating AM species are somewhat diffi cult to explain. There is differential
occurrence of Canadian pondweed ( Elodea ),
water lilies ( Nymphaea ), hornwort ( Ceratophyllum )
and so on. Nevertheless, the emergent and the
fl oating AM greatly enhance the visual attractiveness of the lakes. They are also important for
augmenting habitat diversity of the site. On the
other hand, the submerged AM play an important role in supporting plankton and young fi sh
populations. Both of these are of crucial importance to anglers.
6.8.1 An Account of Fishes
of the Gravel-Pit Lakes
It may be noted here that new gravel pits provide habitat for anglers. They help in relieving
pressure on natural waterside places and help to
satisfy the enormous demand for this activity. It
is interesting to note that more people in Britain
go for fi shing, particularly the ‘coarse fi sh’, like
the roach ( Rutilus rutilus ), perch ( Perca fl uviatilis ), tench ( Tinca tinca ) and carp (usually
Cyprinus carpio ).
The adult carp and tench feed primarily on the
mud-dwelling fauna at the bottom of the lake.
However, most species of fi sh feed on zooplankton
(ZP), e.g . Daphnia . In the gravel-pit lakes, large
species of Cladocera, such as Sida crystallina
and Simocephalus vetulus , do not occur in the
open water but are found in the weed beds only,
where the fi sh is more unlikely to get them. The
larger forms of ZP are quite abundantly found in
the weed beds during summer. But their population generally decline in the open water because
of consumption by the young fi sh. The AM provide essential refuge to cladocerans, without
which they would probably perish. Further, many
fi sh spawn on the underwater parts of AM. The
newly hatched fry rely on the dense protective
AM nursery to shelter them from predation by
perch, pike, etc.
In addition to above, the weed beds also harbour large invertebrates, e.g . insect larvae and
snails, which are diets of many fi sh. These are
particularly signifi cant of new lakes which are
yet to develop benthic fauna on which the fi shes
could feed on. But the anglers try to eradicate the
weeds in view of impediments in fi shing. Fishery
managers must therefore strike a balance by
seeking compromise between clearing enough
weed to satisfy the fi shermen and leaving suffi -
cient to ensure that there will be enough to support the fi sh they wish to catch.
6.8.2 Some Points on Conservation
in Connection with Gravel-Pit
Lakes
Gravel-pit lakes have considerable potential as
sites for wildlife conservation. It is possible that
some compensation may be gained from gravelpit lakes acting as refuges for aquatic plants and
invertebrates suffering from habitat loss elsewhere as natural and semi-natural wetlands
disappear or are altered by eutrophication.
Gravel-pit lakes are of signifi cant interest to
freshwater biologists. The very differences
between these apparently similar lakes provide
ample opportunities for study of some intriguing
problems which have relevance to the way in
which we use artifi cial ecosystems.
6.9
High Altitude (HA) Lentic
Bodies
HA lentic bodies occur in different parts of the
world.
6 Lakes of the World
by fi ve times that of the Lake District lakes.
Studies have been done on eight such lakes situated in two groups of four, just 4 km apart in the
valley of the River Blackwater which is a tributary of the Thames. The results show wide variations amongst the lakes in spite of their
proximity and similarity in size and age. In particular, differences have been revealed in the
amount of aquatic macrophytes (AM) found in
each lake. The emergent AM occur around the
shore wherever there is a shallow littoral zone.
However, the extent of their development
depends upon the shape of the lake basin and the
amount of shallow water. The variations in the
submerged and fl oating AM species are somewhat diffi cult to explain. There is differential
occurrence of Canadian pondweed ( Elodea ),
water lilies ( Nymphaea ), hornwort ( Ceratophyllum )
and so on. Nevertheless, the emergent and the
fl oating AM greatly enhance the visual attractiveness of the lakes. They are also important for
augmenting habitat diversity of the site. On the
other hand, the submerged AM play an important role in supporting plankton and young fi sh
populations. Both of these are of crucial importance to anglers.
6.8.1 An Account of Fishes
of the Gravel-Pit Lakes
It may be noted here that new gravel pits provide habitat for anglers. They help in relieving
pressure on natural waterside places and help to
satisfy the enormous demand for this activity. It
is interesting to note that more people in Britain
go for fi shing, particularly the ‘coarse fi sh’, like
the roach ( Rutilus rutilus ), perch ( Perca fl uviatilis ), tench ( Tinca tinca ) and carp (usually
Cyprinus carpio ).
The adult carp and tench feed primarily on the
mud-dwelling fauna at the bottom of the lake.
However, most species of fi sh feed on zooplankton
(ZP), e.g . Daphnia . In the gravel-pit lakes, large
species of Cladocera, such as Sida crystallina
and Simocephalus vetulus , do not occur in the
open water but are found in the weed beds only,
where the fi sh is more unlikely to get them. The
larger forms of ZP are quite abundantly found in
the weed beds during summer. But their population generally decline in the open water because
of consumption by the young fi sh. The AM provide essential refuge to cladocerans, without
which they would probably perish. Further, many
fi sh spawn on the underwater parts of AM. The
newly hatched fry rely on the dense protective
AM nursery to shelter them from predation by
perch, pike, etc.
In addition to above, the weed beds also harbour large invertebrates, e.g . insect larvae and
snails, which are diets of many fi sh. These are
particularly signifi cant of new lakes which are
yet to develop benthic fauna on which the fi shes
could feed on. But the anglers try to eradicate the
weeds in view of impediments in fi shing. Fishery
managers must therefore strike a balance by
seeking compromise between clearing enough
weed to satisfy the fi shermen and leaving suffi -
cient to ensure that there will be enough to support the fi sh they wish to catch.
6.8.2 Some Points on Conservation
in Connection with Gravel-Pit
Lakes
Gravel-pit lakes have considerable potential as
sites for wildlife conservation. It is possible that
some compensation may be gained from gravelpit lakes acting as refuges for aquatic plants and
invertebrates suffering from habitat loss elsewhere as natural and semi-natural wetlands
disappear or are altered by eutrophication.
Gravel-pit lakes are of signifi cant interest to
freshwater biologists. The very differences
between these apparently similar lakes provide
ample opportunities for study of some intriguing
problems which have relevance to the way in
which we use artifi cial ecosystems.
6.9
High Altitude (HA) Lentic
Bodies
HA lentic bodies occur in different parts of the
world.
6 Lakes of the World