ALL ABOUT THE OTTER
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A
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Otters are
semiaquatic (or in the case of the sea otter, aquatic) mammals. They are
members of the Mustelid family which includes badgers, polecats, martens,
weasels, stoats and minks, and have inhabited the earth for the last 30
million years and over the years have undergone subtle changes to the
carnivore bodies to exploit the rich aquatic environment. Otters have long
thin body and short legs—ideal for pushing dense undergrowth or hunting in
tunnels. An adult male may be up to 4 feet long and 30 pounds. Females are
smaller, around 16 pounds typically. The Eurasian otter’s nose is about the
smallest among the otter species and has a characteristic shape described
as a shallow “W”. An otter’s tail (or rudder, or stern) is stout at the
base and tapers towards the tip where it flattens. This forms part of the
propulsion unit when swimming fast under water. Otter fur consists of two
types of hair: stout guard hairs which form a waterproof outer covering,
and under-fur which is dense and fine, equivalent to an otter’s thermal
underwear. The fur must be kept in good condition by grooming. Sea water
reduces the waterproofing and insulating qualities of otter fur when salt
water gets in the fur. This is why freshwater pools are important to otters
living on the coast:. After swimming, they wash the salts off in the pools
and then squirm on the ground to rub dry against vegetation.
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B
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Scent is used for hunting on
land, for communication and for detecting danger. Otterine sense of smell
is likely to be similar in sensitivity to dogs. Otters have small eyes and
are probably short-sighted on land. But they do have the ability to modify
the shape of the lens in the eye to make it more spherical, and hence
overcome the refraction of water. In clear water and good light, otters can
hunt fish by sight. The otter’s eyes and nostrils arc placed high on its
head so that it can see and breathe even when the rest of the body is
submerged. The long whiskers growing around the muzzle are used to detect the
presence of fish. They detect regular vibrations caused by the beat of the
fish’s tail as it swims away. This allows otters to hunt even in very murky
water. Underwater, the otter holds its legs against the body, except for
steering, and the hind end of the body is flexed in a series of vertical
undulations. River otters have webbing which extends for much of the length
of each digit, though not to the very end. Giant otters and sea otters have
even more prominent webs, while the Asian short-clawed otter has no
webbing—they hunt for shrimps in ditches and paddy fields so they don’t
need the swimming speed. Otter ears are protected by valves which close
them against water pressure.
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C
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A number of
constraints and preferences limit suitable habitats for otters. Water is a
must and the rivers must be large enough to support a healthy population of
fish. Being such shy and wary creatures, they will prefer territories where
man’s activities do not impinge greatly. Of course, there must also be no
other otter already in residence—this has only become significant again
recently as populations start to recover. A typical range for a male river
otter might be 25km of river, a female’s range less than half this.
However, the productivity of the river affects this hugely and one study
found male ranges between 12 and 80km. Coastal otters have a much more
abundant food supply and ranges for males and females may be just a few
kilometers of coastline. Because male ranges are usually larger, a male
otter may find his range overlaps with two or three females. Otters will
eat anything that they can get hold of—there are records of sparrows and
snakes and slugs being gobbled. Apart from fish the most common prey are
crayfish, crabs and water birds. Small mammals are occasionally taken, most
commonly rabbits but sometimes even moles.
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D
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Eurasian otters will breed any
time where food is readily available. In places where condition is more
severe, Sweden for example where the lakes are frozen for much of winter,
cubs are born in Spring. This ensures that they are well grown before
severe weather returns. In the Shetlands, cubs are born in summer when fish
is more abundant. Though otters can breed every year, some do not. Again,
this depends on food availability. Other factors such as food range and
quality of the female may have an effect. Gestation for Eurasian otter is
63 days, with the exception of North American river otter whose embryos may
undergo delayed implantation.
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E
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Otters
normally give birth in more secure dens to avoid disturbances. Nests are
lined with bedding (reeds, waterside plants, grass) to keep the cubs warm
while mummy is away feeding. Litter Size varies between 1 and 5 (2 or 3
being the most common). For some unknown reason, coastal otters tend to
produce smaller litters. At five weeks they open their eyes—a tiny cub of
700g. At seven weeks they’re weaned onto solid food. At ten weeks they
leave the nest, blinking into daylight for the first time. After three
months they finally meet the water and learn to swim. After eight months
they are hunting, though the mother still provides a lot of food herself.
Finally, after nine months she can chase them all away with a clear
conscience, and relax—until the next fella shows up.
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F
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The plight of the British
otter was recognised in the early 60s, but it wasn’t until the late 70s
that the chief cause was discovered. Pesticides, such as dieldrin and
aldrin, were first used in ‘1955 in agriculture and other industries—these
chemicals are very persistent and had already been recognised as the cause
of huge declines in the population of peregrine falcons, sparrow hawks and
other predators. The pesticides entered the river systems and the food
chain—micro-organisms, fish and finally otters, with every step increasing
the concentration of the chemicals. From 1962 the chemicals were phased
out, but while some species recovered quickly, otter numbers did not—and
continued to fall into the 80s. This was probably due mainly to habitat
destruction and road deaths. Acting on populations fragmented by the sudden
decimation in the 50s and 60s, the loss of just a handful of otters in one
area can make an entire population enviable and spell the end.
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G
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Otter numbers
are recovering all around Britain—populations are growing again in the few
areas where they had remained and have expanded from those areas into the
rest of the country. This is almost entirely due to law and conservation
efforts, slowing down and reversing the destruction of suitable otter
habitat and reintroductions from captive breeding programs. Releasing
captive-bred otters is seen by many as a last resort. The argument runs
that where there is no suitable habitat for them they will not survive
after release and when1 there is suitable habitat; natural populations
should be able to expand into the area. However, reintroducing animals into
a fragmented and fragile population may add just enough impetus for it to
stabilise and expand, rather than die out. This is what the Otter Trust
accomplished in Norfolk, where the otter population may have been as low as
twenty animals at the beginning of the 1980s. The Otter Trust has now
finished its captive breeding program entirely. Great news because it means
it is no longer’ needed.
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Questions 1-9
Reading Passage 1 has seven
paragraphs, A-G.
Which paragraph contains the
following information?
Write the correct letter, A-G,
in boxes 1-9 on your answer sheet.
NB You may use any
letter more than once.
1 A description of how otters regulate vision
underwater
2 The fit-for-purpose characteristics of otter’s body
shape
3 A reference to an underdeveloped sense
4 An explanation of why agriculture failed in otter
conservation efforts
5 A description of some of the otter’s social
characteristics
6 A description of how baby otters grow
7 The conflicted opinions on how to preserve
8 A reference to a legislative act
9 An explanation of how otters compensate for heat loss
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Questions 10-13
Answer the questions below.
Choose NO MORE THAN TWO WORDS
from the passage for each answer.
Write your answers in boxes 10-13
on your answer sheet.
10. What affects the outer fur of otters?
11. What skill is not necessary for Asian short-clawed otters?
12. Which type of otters has the shortest range?
13. Which type of animals do otters hunt occasionally?
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