The
Otter – (Lutra lutra)
Population
changes in relation to PCB concentrations in the nature
Emelie Joelsson
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Genus: Lutra
In
The
province where I come from, Smaland, is represented by the otter.
Around 100
years ago the otter was a very common animal all over
Seven years
ago (1999) the total PCB concentration in southern Sweden were still high and
there were weak indications of improvement of the population according to A.
Roos, E. Greyerz, M. Olsson, F. Sandegren.
But
recently the researchers have seen some signs that show that the otter
population is slowly growing .The most clear sign is that there has been a few
animals found that had been hit by cars when crossing roads.
Even if
that is not a good thing itself, researchers see it as a positive sign; the
otter is slowly starting to come back to the region it represents.
The spreading of otters in
The body
length of an otter can vary from 53-
The normal
weight of a male is 8-12 kilos and of a female 6-8 kilos. Occasionally otters
can weight up to 17 kilos.
The otter
lives in both salt- and fresh water, from coast to lakes and watercourses.
It’s well
adapted to a life in water and catches its prey in shallow waters. They live
mainly on fish and crayfish, but also frogs and occasionally mammals are eaten.
A grown up
otter eats about 1-1, 3 kilos of fish every day.
Around 2
years of age the females are getting sexually mature and about 2 month after copulation
they give birth to 1-4 young’s in a burrow near water.
Births can
occur during the whole year but the normal period in
The most
believed reason why the otter population was so strongly decreased is the
amount of pollutant in the water, mainly PCB ( Polychlorinated biphenyl), that
affects the reproduction strongly negative. Since the normal reproduction of
otters is already slow the effects was especially strong.
According
to A. Roos, E. Greyerz, M.Olsson, F. Sandegran the conclusion that PCB was the
main reason for the decreasing otter population, is based on results from an
experimental study on the mink (Mustela
vision), another mustelid which is very sensitive to PCB but not to DDT.
When the minks where given a mixture of PCB their reproduction were severely
decreased.
PCB is transmitted
from the mother to the young via the mother’s milk and the young’s then get a
high dose of PCB in early age. When the young’s start to eat fish their
concentration of PCB tend to decrease.
Researchers
have found out that females have a lower concentration of PCB when they are
lactating, at the same time their young’s can have a concentration that’s 46
times higher than their mother. In this way the lactating females tend to be
detoxified.
The highest
concentrations of PCB are therefore found in juvenile animals.
If the
researchers are right the concentration of PCB should be higher in the male
part of a population than in the female since the males don’t have the ability
of detoxication through lactation.
The
increased hunting and traffic also contributed to the decreasing number of
otters as well as the rearrangement of watercourses.
PCB was
released in the nature for decades before the extent of the damage was
understood.
After that
it took some additional time before the effects of the measure against the
spreading of PCB reached a level where the affected species could start to
recover.
That is
where we are today and hopefully the otter population continues to increase as
the PCB in the nature slowly decreases.
Sources:
http://www.naturvardsverket.se/
http://www.nordensark.se/Utter.htm
http://www.jagareforbundet.se/viltvetande/ovrigaarter/utter.asp
http://www.bioresurs.uu.se/myller/hav/utter.htm
www.elsevier.com/locate/envpol