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Snow, Ice And
Water
The golden fish of the arctic |
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In much of the Arctic the waters are
oligotrophic (literally 'little nourishment') because they are derived
from ice and snow and the hard rocks provide few nutrients. Despite
the lack of nutrients algae grow well even below the ice in frozen
lakes and provide the basis for the food chain in the High Arctic.
The algae are grazed by a variety of crustaceans (water fleas and
fairy shrimps) and insect larvae which are preyed on by the Arctic
char - the Golden Fish of the Arctic - which is the only fish living
naturally in the High Arctic lakes.
It is extremely successful, living to 25 years or more, growing
up to 15-16 kg and distributed throughout the circumpolar region.
This one species illustrates many of the key features of freshwater
biology, and of Human ecology, in the North. |
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The Arctic char is genetically adapted
to survive low temperatures and its distribution extends up into
the islands of the far North such as Svalbard (or Spitspergen as
it used to be called). It lives for most of the year in the rivers
and lakes but migrates to coastal waters for 1-2 months in summer
to feed on the rich food supply before returning to breed. The age
of maturity varies widely and spawning may take place every year,
every two years or less frequently, depending on environmental conditions.
But some populations also live year round in landlocked lakes and
may develop particular characteristics different from those in distant
lakes. Populations sometimes show two distinct size groups, a smaller
group feeding on the bottom fauna and zooplankton while a larger
group feeds on the smaller group - cannibalism. They resemble two
different species. Thus, at the northern edge of its range where
it is the only fish species, the Arctic char shows a highly flexible
life style. |
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Further South, or at lower altitudes,
the Arctic char overlaps with other fish species which cannot withstand
very low temperatures but are competitors in warmer waters. Where
it lives with the brown trout in northern Sweden, the Arctic char
tends to feed on zooplankton in the surface waters while the trout
utilises the bottom fauna. But in winter the char continues to feed
and moves to the bottom while the trout tends to stop feeding because
it is less well adapted to low temperatures. A similar pattern of
co-existence through seasonal partitioning of resources occurs between
the Arctic char and the brook trout (sometimes known as brook char)
in eastern Canada. As the number of fish species sharing the habitat
increases even further, the diet of the char becomes even more limited
until eventually it cannot survive. |
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Thus the ecological 'niche' of the
Arctic char, and its variation in size and other biological features,
are very wide at the northern edge of its range. The niche and life
history are more restricted by competition from less cold-tolerant
species when biodiversity increases towards the southern edge of
its range (environmental gradients again!). |
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The ecological features shown by the
Arctic char illustrate the flexibility that is probably widespread,
but not so obvious, amongst northern animals and plants. Further,
the Arctic char can also interbreed with closely related species
such as brook trout. Interbreeding is a feature of many northern
fish species, suggesting that evolution is still in progress in
this young region. |
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Human ecology has also had
a great influence on the ecology of the Arctic char. The following
catalogue of local and general influences, illustrate the general
role of Humans in the North: |
Fishing on Kamchatka River, Russian Federation. The Association
of Native People of Bystrinsky District catches fish to distribute
to poor and elderly native people in the districts. Photo:Emma Wilson,
1998 |
For hundreds of years, the Inuit people
in Greenland and Arctic Canada chose sites for permanent settlement
to harvest sea-run fish. Sami people traditionally stocked alpine
freshwaters with char to establish larders along reindeer migration
paths.
Long-term selective fishing with gillnets removes larger fish,
affecting population structure and life history traits. Use of
poison and dynamite has eliminated populations on Svalbard. Repeated
total removal of migrating fish using stone weirs ('saputit')
has led to elimination of local populations Greenland.
Widespread construction of hydroelectric reservoirs has
changed water levels, reduced shoreline spawning, increased open
water and limited feeding options.
Overfishing of important prey species (capelin, Arctic
cod) has reduced food supplies during important periods at sea
for migrating char.
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Introduction of other fish species
and freshwater shrimps to 'improve' fishing has reduced char through
competition, caused genetic changes through interbreeding, and affected
food chains. Other unexpected results have been, for example, reduction
or loss of populations of oldsquaw and longtail ducks and predators
of fish (loons, mergansers and ospreys). |
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Acidification by atmospheric
contaminants from southern regions, accumulated in snow over the
long winter, are released as an acid pulse by the spring thaw. This
has eliminated fish from many northern Scandinavian lakes, enhancing
zooplankton and insect feeding birds but reducing fish feeders.
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Persistent organic pollutants (POPs), including many pesticides,
are transported to the North, accumulate in fatty tissues and
are concentrated up the food chain (biomagnification). Arctic
char are at an intermediate stage in the chain and many populations
have levels which are above national guidelines (see
figure 10)
Climate warming is going to enable competitors to survive
better where they are already at their northern margins change
of their range. The previous advantage of winter feeding by char
will be reduced because warming is expected to be greatest in
winter. Char will tend to increase their range in the far North
but loose ground in the South.
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