State of Nature report - RSPB

MARINE
ere we provide a brief overview of how marine species
are doing, but for a more comprehensive analysis,
please refer to the UK-wide marine assessment
Charting Progress 2. Similar assessments are available for
Scotland, Northern Ireland and the Isle of Man.
We lack the necessary evidence on abundance to develop
long-term trends for many marine species. For example, for
most regions we do not know trends for our 11 regularly
occurring species of cetacean, although we do know in
some cases that declines have occurred. However, all recent
assessments paint a mixed picture of nature under varying,
but often severe, pressure from human activities.
Since 1996, harbour seals have declined by 31% in Scottish
waters, particularly around Orkney (which showed a 66%
decline) and northern Scotland, due to a combination of
factors including pollution, disease, prey availability and
competition with grey seals 2 . From the 1950s to the
1990s, grey seal pup production increased consistently,
but it is no longer increasing in some regions 1 .
As the threat from human hunting progressively reduced,
and seabirds began to exploit fisheries discards, the number
of seabirds breeding in the UK increased from around 4.5
million in the late 1960s to 7 million by the end of the 1990s.
However, this figure masks considerable variation between
species. Roseate terns, herring gulls and Arctic skuas have all
declined by more than half within the last 40 years. In 2004,
2005 and 2007, the breeding success of 21 seabird species
was at its lowest level since the mid 1980s (see Figure 23).
Seabirds nesting in Scotland have fared particularly badly,
with sharp declines for species such as the Arctic skua.
The kittiwake has declined substantially (by 41% since 2000),
whereas populations of other widespread species, such as
120
100
% of fish over 40 cm
50
45
40
35
30
25
20
15
10
5
0
1982
1984
Northern North Sea
Southern North Sea
OSPAR EcoQO target
1986
1988
1990
1992
1994
the guillemot and razorbill, appear to have remained relatively
stable. Evidence suggests that for many species, including
the kittiwake, declines are caused by changes in sandeel
availability, at least in part due to factors related to
climate change.
There is evidence that sub-tidal marine sediment habitats
have been damaged over large areas by fishing activity, in
particular by bottom-trawl and scallop dredge gear. Such
activities can have huge impacts on bottom-dwellers such
as the ocean quahog, a remarkable bivalve mollusc that can
live for 500 years. At a more local scale, these activities also
damage sensitive features, such as maerl beds and seagrass,
that shelter a range of wildlife.
Finally, sharks, skates and rays face continuing declines and
are severely depleted all around the Scottish coast, in part
due to overfishing 2 . Elsewhere, most commercial fish stocks
around the UK remain depleted (see Figure 24), though there
have been improvements in stocks of certain species in the
last 5–10 years 6 . Historically, however, national and international
fish landings are a fraction of the highs in the 1960s and
1970s, and generally smaller than in the early 20th century.
The problems of overfishing and discards are being discussed
as part of the reform of the EU Common Fisheries Policy.
1996
Year
1998
2000
2002
2004
2006
2008
2010
Index (1986 = 100)
80
60
40
20
0
1986
1988
Productivity
Abundance
1990
1992
1994
1996
1998
Year
2000
2002
2004
2006
2008
2010
The continuous plankton recorder has been monitoring
plankton in UK waters since 1931 7 . These small plants
and animals form the base of our marine food webs and
play a pivotal role in the ecosystem by regulating larval
fish stocks. Since 1950, there have been substantial changes
to the main animal group within the plankton – copepods.
The total abundance of copepods has declined markedly,
and the species present are changing as the sea warms.
Already, these changes are negatively affecting fish
species, such as cod, as well as seabirds.
62 STATE OF NATURE 2013