The UK’s marine environment holds internationally important numbers of birds. Since these birds are top predators in several different marine habitats, changes lower down the food chain are likely to be manifested in their populations, making them a useful indicator of the state of our seas.

More than 100 species regularly use the marine areas in the UK. The majority of these species are waterbirds such as waders, herons, egrets, ducks, geese, swans, divers and grebes, and seabirds such as petrels, gannets, cormorants, skuas, gulls, terns and auks.

Seabird and waterbird populations in the UK have increased in size over the past century as a direct result of increased protection from hunting and persecution in the UK and overseas. But since around the mid-1990s, declines in numbers of both wintering waterbirds and breeding seabirds indicate that pressure is once again being exerted on marine bird populations.

We made a separate assessment of the magnitude of the impacts of pressures from human activities on seabirds and waterbirds, using eight broad pressure themes, encompassing 22 pressures. We based our assessments on expert judgement, supported by published evidence where possible.

Waterbirds

Most internationally important aggregations of waterbird species in the UK marine environment occur during spring and autumn migrations and during winter in areas such as estuaries where food is accessible and abundant.

Our assessment of the status of waterbirds in the UK used data on non-breeding birds collected by the Wetland Bird Survey (WeBS), that have baseline levels from winter 1975/76. Numbers of waterbirds (based on a subset of 32 out of 57 species) wintering in or migrating through marine areas in the UK doubled on average (they increased by 106%) between the mid-1970s and the mid-1990s. Since then, average numbers have declined slightly, but in the winter of 2006/07, they were still 85% higher than in the mid-1970s when co-ordinated monitoring began (see Figure 3.5). However, some species of diving duck and estuarine wader have recently declinedmore substantially: in 2006/07 there were 43% fewer goldeneye, 54% fewer dunlin and 28% fewer bar-tailed godwit than in 1975/76 (see Figure 3.6).

Figure 3.6 Percentage change in the numbers of non-breeding waterbirds around the coast of the UK over the short-term (past 5 years), medium-term (past 10 years) and long-term (past 25 years).

The trends in abundance of most species of waterbird in coastal Special Protection Areas (SPAs) have been similar to those at other sites around the coast of Britain (comparative data were not available for Northern Ireland): waterbirds are faring no better or no worse on sites that are not SPAs.

Of the sixteen pressures identified as having potential impacts on the UK waterbird populations, the five most significant were: climate change, contamination by hazardous substances, removal of species (target and nontarget), habitat damage, and habitat loss.

Severe winter weather in the past has increased the mortality of some species. It follows that the milder weather in recent years as a consequence of climate change has enabled more birds to survive through the winter. However, such benefits may be countered in the future by the negative impacts of ‘coastal squeeze’ as rising sea levels lead to the loss of intertidal feeding areas. Climate change may already be contributing to recent declines in the numbers of some species, including bar-tailed godwit, grey plover, dunlin and ringed plover, by encouraging a north-eastwards shift in their distribution. As a result, more birds are now wintering on the east coast of Britain and fewer birds are wintering in the south-west. We do not yet know if in the future, the birds will continue to move northeastwards and relocate elsewhere in Europe, or if total numbers migrating through and wintering in Europe will decline as a consequence of these climate-related changes. A trend towards milder winters has allowed more birds to take advantage of the richer feeding in the muddier east coast estuaries with a much reduced risk of cold weather mortality. Total numbers of waders wintering in the UK may be starting to decline as more birds move eastward and overwinter along the coasts of mainland Europe.

Waterbirds such as seaduck, divers and grebes have a low resistance to the effects of contamination by surface pollutants such as oil. However, while oiled birds can be found on beaches, there have been no major oil spills in the past five years that would have an effect on waterbird populations.

Detailed studies carried out on The Wash found marked reductions in waterbird survival as a result of shellfish harvesting. Shellfisheries can also cause substantial changes to marine ecosystems; disturbance of the seafloor leads to mortality of benthic organisms, and re-working of the sediment, which in turn reduces the availability of food to waterbirds.

Most species of waterbird, but especially waders, are affected by activities such as coastal defences, land claim, construction of tidal barrages, and the construction and extension of marinas or harbour developments that result in the loss of suitable habitat. Habitat damage caused by bottom trawling, shipping activities, dredging and sand/gravel extraction, can substantially reduce the availability of some invertebrate prey (e.g. bivalves) that is likely to drive changes in the numbers and distribution of seaduck, divers and waders that feed on them.

Seabirds

Large numbers of seabirds occur in UK waters all year round, but some species are only present during the breeding season, over winter or during migration. Most seabirds spend the majority of their lives at sea: some are confined to inshore waters, but others venture much further offshore. Seabirds feed mainly on fish, squid and plankton, or pick detritus from the surface, while gulls also forage on exposed intertidal areas.

The state of seabird populations was assessed using data on numbers and breeding success collected by the Seabird Monitoring Programme (SMP). 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. Since Charting Progress the total number of breeding seabirds has decreased by around 9% (Figure 3.5) although changes in breeding numbers have varied greatly between individual species (Figure 3.7). Of the seabird species breeding in the UK, only northern gannet and great skua have sustained a positive trend in population size since 1969 when comprehensive monitoring of breeding numbers began. Conversely herring gull and roseate tern numbers have declined the most since 1969 – by more than 50%. The mean breeding success of a sample of 21 seabird species was at its lowest levels in 2004, 2005 and 2007 since monitoring began in the mid-1980s (Figure 3.8). These falls in breeding success have been most acute in black-legged kittiwakes and other species such as common guillemot that rely on sandeels (Figure 3.8), and more so on Britain’s North Sea coast. There is strong evidence that climate-driven changes in the food chain have had acute negative impacts on seabirds. Changes in the North Sea plankton community in the late 1980s caused by rising sea temperatures has led to large reductions in abundance of the zooplankton on which larval fish feed and poor sandeel productivity is associated with warmer sea-surface temperatures.

Figure 3.7 Percentage change in the numbers of seabirds breeding in the UK over the short-term (2000-2008), medium-term (1986-2008) and long-term (1970-2008).

Fisheries may also have contributed to a reduction in sandeel availability and quality. For instance, off south-eastern Scotland in the 1990s, a sandeel fishery significantly depressed the adult survival and breeding success of blacklegged kittiwakes compared with years prior to the fishery opening and after it was closed in 2000.

For decades, some seabirds have benefited from fisheries through food provided at sea by discharging offal and discarding undersize fish. As a result, the abundance of scavenging species such as great skua and northern fulmar may have been elevated above levels that naturally occurring food sources could sustain. A subsequent decline in numbers of northern fulmar since the 1990s may be linked to a reduction in fisheries effort. However, there was insufficient evidence for us to assess the scale of the pressure from fisheries.

In addition to climate change and the removal of target and non-target species through fishing, five other pressures were identified as having potential impacts on the UK seabird populations (contamination by hazardous substances, litter, visual disturbance, introduction of non-indigenous species, habitat loss); the most significant of these was the introduction of nonindigenous species. The long-term existence of non-indigenous predatory mammals such as brown rats on offshore islands, following intentional or accidental introductions, has significantly reduced the numbers of ground-nesting seabirds such as storm-petrels and Atlantic puffins. Depredation of seabird eggs, chicks and adults by North American mink has led to reductions in seabird breeding success, breeding numbers and eventual extinction of whole colonies in the Western Isles and on numerous islands throughout the Minches and Western Scotland. However, the control of mink and hedgehogs in parts of the Western Isles (funded under the EU Life programme) and elsewhere in north-western Scotland and the eradication of rats from some offshore islands in western Britain such as Canna and Lundy has led to increases in numbers and breeding success at some seabird colonies and to the complete recovery of others.

Future work

The limited availability of data meant that we had to confine our assessment to breeding seabird populations and to migrant and overwintering populations of waterbirds in intertidal areas or close inshore.

Although we considered the impact of climate change on seabirds to be high, much of the evidence for this is correlative rather than demonstrably causal. We need to better understand the nature of the interactions between climate, plankton, sandeels, fishing and seabirds in order to predict the likely magnitude of future impacts on seabirds and to devise measures that may mitigate the impacts of climate change. We also need more research to determine the extent of the impact of nonindigenous mammalian predators on island seabird colonies around the UK.

There is as yet no data on how many seabirds from UK colonies are killed as a result of becoming entangled in fishing nets or taking the baited hooks of long-line fisheries operating within and outside UK waters. Past evidence from the Norwegian long-line fleet suggests that large enough numbers could be killed to have a significant effect on the populations of some species.

We had only low confidence in the assessment of impacts of habitat loss on both seabirds and waterbirds. Habitat loss and damage are likely to increase in the future due to coastal squeeze and through expansions in offshore renewable energy generation and in sea defence/realignment. It is important to assess the cumulative impact of all these activities and pressures.

We will also need further work to establish indicators and targets for determining Good Environmental Status as part of the UK’s implementation of the EU Marine Strategy Framework Directive.