State of Nature report - RSPB

FRESHWATER AND WETLANDS
The freshwater pearl mussel, one of the
most threatened molluscs in the world,
is a fascinating species that can grow
to 15cm long and live for more than
100 years.
It has suffered huge declines in England
and Wales in the last 40–50 years,
but Scotland retains globally important
numbers, with perhaps half of the
world’s viable populations 6 . But even
there, declines continue: between
1970 and 1998, it is thought this
species was lost from two rivers
every year.
There are many reasons for the decline,
including sedimentation, pollution by
nutrients, heavy metals and pesticides,
water abstraction, river engineering
and competition from non-native
species such as the American signal
crayfish. The decline in salmon, which
act as larval hosts, has also affected
these mussels.
In addition, freshwater pearl mussels
are collected illegally, although much
work is underway to combat what is
perhaps the greatest problem for this
threatened species.
reshwater habitats receive
some of the most intensive and
expensive conservation measures
to control pollution, manage habitats
and respond to threats. There are many
well-documented examples of badly
damaged rivers being improved as a
result of sewage treatment, although
many river systems remain damaged.
Following a decline in acid rain, we
have seen the first signs of recovery
in freshwater habitats 21 , but there is
still a long way to go.
Agri-environment schemes include
many measures to protect freshwater
habitats. However, evidence of their
effectiveness is currently limited. Early
evidence does suggest that better
control of the problems associated
with livestock farming, such as slurry
pollution, is helping habitats to recover.
Creation of new ponds and wetland
habitat for freshwater wildlife such
as bitterns, great crested newts
and nutrient-sensitive water plants
seems to be particularly successful.
Compared to many other habitats,
functioning and wildlife-rich wetlands
can be restored or created in a relatively
short time. For instance, at Loch Leven,
long-term nutrient management has
allowed the number and diversity of
aquatic plants to increase, providing
better habitat for fish and birds 22 .
Freshwater habitats are often isolated
and so are vulnerable to the impacts of
invasive non-native species. Establishing
early warning and rapid response
systems to deal with newly-established
introduced species is critical to protect
these habitats in the future.
Otters are a true conservation success story. Once widespread across the UK, they
suffered a dramatic decline during the 1950s and 1960s, in part due to pesticide
pollution. Following concerted conservation effort, including the withdrawal of
damaging chemicals, sympathetic habitat management and local introductions,
otters have bounced back and reclaimed most of their former range 9 – to date the
only freshwater species to do so. In 2011, otters were discovered on the Medway and
Eden rivers in Kent, a milestone which marked their return to every county in the UK 23 .
% of survey sites showing signs of otters
90
80
70
60
50
40
30
20
Northumbria
Yorkshire
Trent
Anglian
South West
Southern
10
0
1977–79 1984–86 1991–94 2000–02 2009–10
Year
50 STATE OF NATURE 2013